***Useful Information For The Working Sparky***

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“ Rcd's “

Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1 All circuits in a bath shower room must be protected by a 30mA RCD. P166, 701.411.3.3
Where applicable an RCD notice must be fixed on or next to the CCU 514.12.2 An RCD should not be used as a main switch 314.2 If the maximum Zs values for a circuit in a TN systems cannot be met, the circuit may be protected by a 30mA RCD. 531.3.1
If the maximum Zs values for a TN systems cannot be met, the installation may be protected by an 100mA RCD and treated as a TT systems . 531.3.1 : 411.5.1 : 411.5.2 : 411.5.3
Unless specifically labelled or suitably identified, all 13A socket outlets must be protected by a 30mA Rcd. 411.3.3
In a TN systems , the part of a lighting circuit in a bath or shower room is required to be 30mA RCD protected. 411.3.3 , 701.411.3.3

Where a cable is buried in a wall or partition at a depth of less than 50mm on either side it must be sufficiently mechanically protected against penetration OR RCD protected AND installed either horizontally within 150mm of the top of the wall or vertically within 150mm of the angle formed where two walls meet or run horizontally or vertically to an accessory, luminaire or CCU 522.6.6 , 522.6.7 . This applies to a cable in a partition constructed using metallic parts other than fixings irrespective of the cable depth. 522.6.8

Surface run cables do not require RCD protection. OSG p22

A single RCD protecting a TT systems must be installed at the origin of the installation unless the part of the system between the origin and the RCD fulfils the requirements for protection by Class 11 equipment or equivalent insulation 531.4.1

All Electrical equipment must be accessible for operation , inspection & testing maintenance and repair. 132.12

Rcd Test Procedure

Many RCD test meters have a facility where tests can be carried out during the positive or negative half of the supply cycle. For tests 1 & 2 the RCD operating time to be recorded is the longer of the two measured during the half cycle tests.

DO NOT press the test button on the RCD before testing as this can temporarily reset a faulty RCD

Test 1
Adjust the current setting on the test meter to 100% of the rated trip current of the RCD and perform a test. A general purpose BS4293 RCD should operate within 200mS . A general purpose BS-61008 RCD or RCBO to BS-61009 should operate within 300ms

Test 2
An RCD provided for Basic Protection should have a rated TRIP current not exceeding 30mA If the RCD is rated at 30mA , adjust the current setting on the test meter to 150ma ( x5 ) and perform a test. The RCD must operate in a time not exceeding 40mS.
Test 3
Adjust the current setting on the test meter to 50% of the RCD trip current and perform a test. The RCD should not operate within 2 seconds
The Test Button : Finally operate the RCD by pressing its test button

 

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17th Edition Wiring Regulations Practice : Apprentice ,
Overall Percentage Score , 100%

Unit 1: Special installations or locations ( 100% )
Q1 : Zone O in a bathroom is the ( A ) Area within the bath or Shower , ( p-165 701.32.2 )
Hint !! Extreme end ,
Q2 : Zone 1 in a bathroom is the
Hint !! Not quite the extreme end , ( A ) Area directly above the bath or shower up to 2.25m above finished floor level . ( p-165 701.32.3 )
Unit 2 : Appendices ( 100% )
Q2 : BS-1362 relates to ( A ) Cartridge fuses for use in 13A plugs , ( p-229 BS – Standards )
Hint !! Used with BS- 1363
Unit 3 : Inspection & Testing ( 100% )
Q3 : An insulation Résistance test performed on a 50v a.c . SELV installation should be capable of producing a test voltage of
( A ) 250v dc ( p-158 / table 61 )
Hint !! think about ELV downlighters and the average voltage they use ,
Testing : Q 21 : An insulation résistance test performed on a 230v a.c installation should be capable of producing a test voltage ,
Hint !! what type powers the instrument ? ( A ) 500v DC ( p-158 / table 61 )
Unit 4 : Definitions ( 100% )
O4 : A double insulated hand held electric drilling machine is known as
Hint !! think about where you see the symbol , ( A ) Class II equipment ,
Q5 : BS-7671 IEE Regulations define Extra Low Voltage a.c as Not exceeding ( A ) 50 volts a.c , ( p-31 )
Unit 5 : Selection & erection of equipment ( 100% )
Q6 : where a wall consists of a metallic construction and it is necessary to install cables within that wall , the circuit should
( A ) be RCD protected ,
Unit 6 : protection for safety ( 100% )
Q7 : A device intended for safety reasons to cut off all or part of an installation from every source of electrical energy provides ,
( A ) Isolation ( 537 / 537.2 )
Q8 : what is the maximum Zs for a 32Amp type B circuit breaker protecting a standard ring final circuit ,
( A ) 144Ω ( p-49 / table 41.3 )
Unit 7 : Scope , Object and fundamental characteristics ( 100% )
Q9 : Inspection & Testing of an installation should be completed by ( A ) Competent person )
Hint !! Maybe someone who knows what they are doing :
Q10 ; BS-7671 is a ( A ) Non-Statutory document ,
Hint !! its Not enforceable in Law ,
Unit 8 : Assessment of general characteristics ( 100% )
Q 11 : Non-sheathed cables for fixed wiring , other than protective conductors , should be installed in , ( A ) Conduit or Trunking ,
Q 12 : who is responsible for specifying the first periodic inspection on an installation ?
Hint !! who knows everything about an installation before the Other ?
( A ) the person responsible for the design ,
Q 13 : Inspection & Testing of an installation should be completed by ?
Hint !! maybe someone who knows what they are doing ,
( A ) Competent persons ,
Q 14 : Basic protection protects against ?
Hint !! the most basic of contact ,
Electric shock under fault free conditions ,
Q 16 : Any overcurrent protective device installed at the origin of a circuit must have a breaking capacity of ?
Hint !! what cases the maximum current to flow under fault conditions ,
( A ) Equivalent or more to the prospective short circuit current ,
Q 17 : Non-sheathed cables for fixing wiring , other than protective conductors , should be installed in ,
Hint !! think what the sheathing provides on cable , ( A ) Conduit or Trunking ,
Q 18 : Undervoltage protection is required where the restoration of power may cause ,
Hint !! what can be dangerous if power is suddenly turned on ?
( A ) Unexpected starting of machinery ,
Q 19 : outdoor lighting involves all the following except ,
Hint !! Temporary installation , ( A ) Festoon lighting ,
Q 20 : where a wall consists of a metallic construction and it is necessary to install cables within that wall the circuit should ?
Hint !! needs additional protection , ( A ) be RCD protected ,

 

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PERIODIC INSPECTION REPORT FOR AN ELECTRICAL INSTALLATION
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 7671 [IEE WIRING REGULATIONS])
Extent and Limitations of the Inspection :
Extent of Electrical Installation covered by this report ,
Limitations ( see Regulation : 634.2 p-163 ,

Insulation resistance
If the DC resistance tests above fail to identify the cause of a circuit that is causing RCD tripping on its own (i.e. without the aid of the appliances usually connected to it). You may find that repeating the tests described using an insulation resistance tester will yield more information. Since the insulation resistance tester carries out the tests at much higher voltages than the multimeter (typically 500V) it will identify those few failures where the conduction path between a live conductor and earth is only visible at mains voltages.
Take care when performing these tests, it is possible to get a nasty shock off an insulation test meter!
Mitigating the effects of nuisance trips
While it is possible to eliminate most causes of nuisance trips with careful system design and testing, it is always wise to design the system to allow for the possibility of it happening:
* Provide dedicated non RCD protected circuits [see note] for vulnerable equipment such as:
*Freezers
* Central Heating Systems
* Heated Aquariums
* Fire or smoke alarms
* Security systems and lighting
* Computer and IT equipment
* Have as few circuits or devices as possible protected by the same RCD so that a trip impacts as few extraneous circuits as possible. The ultimate solution would use RCBOs for each circuit. Obviously expense has to be weighed against the implications of tripping.
* Use emergency lighting to backup any important lighting circuits that need to be RCD protected (i.e. on TT earthing systems). In particular these should include lighting for:
* Stairs
* Fire escape routes
* Near trip hazards or other difficult to navigate areas
* Near the consumer unit
* Consider using uninterruptible power supplies (UPS) to maintain running of critical equipment.
* Power failure alarms might also be an appropriate measure in some circumstances.
Note: With the advent of the 17th edition of the wiring regulations, one must comply with the requirement that any buried cables that don't have 30mA trip RCD protection, must still be adequately protected from physical damage. This can be achieved either via being buried at 50mm or greater depth in a wall, or with metallic earthed protection such as conduit or by using suitable metal sheathed cables like SWA, MICC etc. Note that new cable types are becoming available to help meet these requirements. Surface mounted cables may also be installed without additional RCD protection in some circumstances since it is assumed they are sufficiently visible to avoid accidental damage from drilling / nailing etc.
System design using RCDs
Some of the system design aspects of using RCDs to good effect are covered in the mitigation section above. However the following basic principles should also applied:
1. Use split load consumer units, to allow circuits that do not benefit from RCD protection to be powered directly.
2. Don't place too many circuits on the same RCD. In particular identify circuits that are likely to have high leakage (e.g. those containing lots of IT other electronic equipment).
3. Where RCDs need to be cascaded, use time delayed types for the upstream device so that trips are contained close to the cause of the fault.
4. Don't place circuits to outside electrics and outbuildings on the same RCD as protects the house circuits.
5. Avoid placing high leakage devices on RCD protected circuits where possible.
6. Design circuits such that the anticipated leakage is no more than 25% of the trip threshold. This will allow for later circuit extension.
7. Ensure accessories and wiring are not placed in excessively damp environments.
8. Don't use lower trip threshold devices that is appropriate for the level of risk present and protection sought.

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKSCERTIFICATE :

Scope :
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not
extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to
an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the
replacement of equipment such as accessories or luminaires, but not for the replacement of
distribution boards or similar items. Appropriate inspection and testing, however, should always be
carried out irrespective of the extent of the work undertaken ,

Part 1 Description of minor works :
1,2 The minor works must be so described that the work that is the subject of the certification can be
readily identified.
4 : See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual
circumstances. See also Regulation 633.1

Part 2 Installation details :
2 : The method of fault protection must be clearly identified e.g. earthed equipotential bonding and
automatic disconnection of supply using fuse/circuit-breaker/RCD
4 : If the existing installation lacks either an effective means of earthing or adequate main equipotential
bonding conductors, this must be clearly stated. See Regulation 633.2
Recorded departures from BS-7671 may constitute non-compliance with the Electricity Safety, quality
and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is
important that the client is advised immediately in writing.

Part 3 Essential Tests :
The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor
works. For example, where a socket-outlet is added to an existing circuit it is necessary to ;
1 : establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 : measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 : measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 : check that the polarity of the socket-outlet is correct
5 : (if the work is protected by an RCD) verify the effectiveness of the RCD

Part 4 Declaration :
1,3 The Certificate shall be made out and signed by a competent person in respect of the design , construction, inspection and testing of the work
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the
work undertaken and to the technical standards set down in BS-7671 be fully versed in the inspection
and testing procedures contained in the Regulations and employ adequate testing equipment.
2 : When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting ,

 

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SELV and PELV :

According to IEC 60364-4-41 protection against electric shock is deemed to be provided when:
• the nominal voltage cannot exceed an upper limit in accordance with IEC 60449 (50 V AC / 120 V DC)
• the supply is from a safety isolating transformer in accordance with IEC 60742 or equivalent (e.g. motor generator with windings providing an equivalent isolation)
• an electrochemical source (e.g. battery) or another source independent of a higher voltage circuit (e.g. diesel-driven generator),
• mobile sources or certain electronic devices all complying with appropriate standards, where measures have been taken in order to ensure that, even in the case of an internal fault, the voltage at the outgoing terminals cannot exceed the above mentioned levels , or
• when all above conditions are fulfilled and in addition electrical separation with either SELV for unearthed circuits or PELV for earthed circuits is provided
Arrangement of circuits :

IEC 60364-4-41 states that live parts of SELV and PELV circuits shall be electrically
separated from each other and from other circuits. Arrangements shall ensure electrical separation
not less than that between the input and output circuits of a safety isolating transformer ,
Circuit conductors of each SELV and PELV system shall preferably be physically
separated from those of any other circuit conductors. When this requirement is impracticable, one of the following arrangements is required
• Plugs and socket-outlets of SELV and PELV systems shall comply with the following requirements
– plugs shall not be able to enter socket-outlets of other voltage systems : – socket-outlets shall not admit plugs of other voltage systems :
– socket-outlets shall not have a protective conductor contact :

Requirements for unearthed circuits ( SELV ) :
According to IEC 60364-4-41, live parts of SELV circuits shall not be connected to
earth or to live parts or to protective conductors forming part of other circuits
Exposed conductive parts shall not be intentionally connected to :
* earth; or
* protective conductors or exposed conductive conductors of another circuit; or
* extraneous conductive parts.
If nominal voltage exceeds 25 V AC r.m.s or 60 V ripple-free DC, protection against direct contact shall be provided by:
* barriers or enclosures affording a degree of protection of at least IP2X or IPXXB; or
* insulation capable of withstanding a test voltage of 500 V AC r.m.s for 1 minute ,
In general, protection against direct contact is unnecessary if the nominal voltage
does not exceed 25 V AC r.m.s. or 60 V ripple-free DC. However, it may be necessary under certain
conditions of external influences, which is currently under consideration by the IEC.

 

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Why Earth ?
One side of the electricity supply (the neutral) is firmly connected to earth at the substation to prevent the supply 'floating' relative to earth for safety reasons.
Many electrically operated devices (e.g. washing machines, heaters and some lighting fittings) have exposed metalwork which could become live if a fault occurred. Anyone touching it could then receive a shock or even be killed depending on the current flowing through them to earth. To prevent this, an earthing conductor should be provided to all socket outlets, lighting circuits and any fixed appliances to which exposed metal parts are then connected. The earth connection limits the voltage which can appear on the exposed metal parts under fault conditions to a safe value until the fuse blows or the MCB or RCD trips. Note that earthing does not necessarily prevent anyone receiving a shock, but together with the time/current characteristics of the protective device (fuse, MCB or RCD) it should ensure that it is not lethal. It is desirable to make the impedance (resistance) of the earth wiring a low as practicable. (1000A flowing through 0.1 ohm drops 100V! )
Note that exposed metalwork cannot be protected by connection to the neutral because current flowing will cause a voltage drop between the metalwork and true earth. Also, if the neutral connection breaks or the appliance is plugged into a socket with line and neutral reversed (!), the metalwork will be at full mains voltage.
Appliances with an earth connection are called Class I (one): Class II or 'double insulated' appliances incorporate additional insulation to prevent exposed metalwork becoming live, and do not require an earth connection. This means that a 2-core mains lead can be used and internal earth connections are not needed.
A fundamental principle of electrical safety is that no single fault condition should cause a hazardous situation. This is why some of the regulations may appear to be rather stringent: it is better to be safe than sorry.
Who Supplies the Earth ?
The earth connection will usually be supplied by one of the following methods:
a). By the electricity company. Either through the armouring of the supply cable or through a combined neutral and earth conductor. The latter method is termed PME (protective multiple earthing) and requires some special attention (see below). There will usually be a label near the meter indicating a PME system.
b). Through an earth electrode; usually a rod or plate driven into the ground. This method is found where the electricity company cannot easily supply or guarantee an adequate earth conductor; for example, where the supply comes on a pair of overhead wires. The user is generally responsible for the adequacy of the earth electrode.
The method of earthing can normally be found out by tracing the wiring from the meter/consumer unit. It is usually fairly obvious. IMPORTANT! - It is no longer permitted to use a water or gas pipe for the main or only earthing connection. There may, however be earth bonding wires connected onto the water and gas pipes for 'equipotential bonding' (see below). If there is no electricity company earth or dedicated separate earth electrode, then one must be provided. Contact the electricity company if in any doubt.

Earthing of Electrical Installation :
Each circuit requires an earth conductor to accompany (but kept separate from) the line and neutral conductors throughout the distribution. Where the distribution is in the form of a ring, the earth connection must also complete the ring.
The bare tails of earth conductors must be insulated with green/yellow sleeving from the exit from the cable sheath to the earth terminal.
All metal boxes should be connected to the earth; either through a short tail covered with green/yellow sleeving to the socket earth terminal or directly by the earth conductor for a switch box.
Equipotential Bonding
As mentioned elsewhere, a fault current flowing in the earth wiring will cause the voltage on that wiring to rise relative to true earth potential. This could cause a shock to someone touching, for instance, the case of a faulty washing machine and a water tap at the same time. In order to minimise this risk, an 'equipotential zone' is created by connecting the services to the main earthing point. Such services are:
• Water Pipes
• Gas Pipes
• Oil Pipes
• Central Heating
• Metallic Ventilation Trunking
• Exposed Parts of Building Structure
• Lightning Conductor
• Any other Metallic Service

WHY DO LIGHT BULBS ALWAYS BLOW WHEN YOU SWITCH THEM ON, AND WHY DO THEY BLOW FUSES ?
An ordinary incandescent "light bulb" consists of a thin tungsten filament in a glass envelope containing an inert gas. The filament has a relatively high resistance, and thus gets hot - hot enough to give out useful amounts of light as well as lots of heat - when current is flowing through it. The inert gas prevents the hot tungsten rapidly oxidising, as it would in air, or rapidly evaporating, as it would in a vacuum. It does, however, reduce efficiency, by conducting heat away from the filament. (Different gases and pressures are selected for different applications: for example, krypton and xenon are advantageous because they convect less and prevent evaporation better than argon/nitrogen, and therefore allow a hotter, more efficient, filament to be used while maintaining lamp life. Note that quartz halogen bulbs are different again: here, evaporated tungsten is re-deposited on the filament, thus allowing it to be hotter still while maintaining its life.)
Tungsten, being a metal, has a resistivity which increases as its temperature rises. Therefore, when you switch on a lamp, it presents a much lower resistance than normal to the passage of electricity, and so your beefy electricity supply will drive through a great deal more current than normal while the filament heats up, putting it under thermal stress as it expands. This on its own encourages the filament to give up and break, but it is exacerbated by the fact that any thinned section will incur extra stress, as it will heat up more quickly than the rest of the filament (being thinner), present a higher resistance, and thus dissipate even more than its fair share of the (increased) power. This will tend to thin it further, rapidly, and hence lead to a point of failure.
How do you deal with it? Well, using a rotary on/off dimmer, where you always have to switch on the lamp at its lowest brightness, will help a lot. A dimmer will reduce the maximum available light output slightly. You can also fit negative temperature coefficient thermistors in series with the bulb. These have a resistance/temperature characteristic with the opposite slope to that of the filament, so give a "soft start" until they themselves warm up. Again, you will lose a little brightness, and waste a little energy in the hot thermistors. I am not aware of any "off the shelf" products containing thermistors, probably because they need to be selected for the wattage of lamp required.
It should be noted, however, that it is probably counterproductive to try to keep a light bulb alive for too long. This is because the thinned filament will be taking less current, so the light output will be reduced, and the tungsten that has evaporated from it will be deposited on the inside of the glass, reducing efficiency by blocking some of the light.
As regards blowing the fuse, this is never directly due to a broken filament falling onto the lead-out wires, and thus presenting a much lower resistance, but is due to the gas or vaporised filament in the bulb becoming ionised. The high temperature and large electric field (full mains voltage across a very small gap) which occurs when the filament breaks can cause the gas to go into a conducting state, and the plasma will "spread" until it shorts out the lead-out wires, because it presents a much lower resistance than the filament. This causes a "pop" due to rapid heating, and has been known to cause the envelope to explode. Light bulbs usually have built-in fuses to deal with this, but as they are built down to a price, they aren't always effective.
If you plug in a new light bulb and it only lasts a few seconds, leaving a white pattern on the glass, this is because it has cracked at some point, letting air in. When energised, the filament has oxidised to white tungsten oxide, which condenses on the glass in a pattern corresponding to the flow of air inside as the lamp is switched on.
Oh, by the way, "extra-long life" bulbs seem to be a con. They just run at a lower temperature than normal bulbs, thus lasting longer, but being a lot less efficient. There is no justification for the extortionate prices charged for them.

 

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Cables in contact with polystyrene

Do not let electrical cables come into contact with polystyrene. It slowly leaches the plasticiser out of the PVC, so that it becomes stiff and brittle. Sometimes it looks like the PVC has melted and run a little.

* Shaver sockets incorporate special isolating transformers which provide an earth-free output. The primary (input) side requires an earth which is connected internally to the transformer core.

Protective Multiple Earthing (PME.)
With PME. the neutral and earth conductors of the supply are combined. The supply company connects the neutral solidly to earth frequently throughout the distribution network. At the customer's connection point the company supplies an 'earth' (which is actually connected to the neutral) to which all the installation earths and equipotential bonding are connected. Note that within the installation, the earth and equipotential bonding are kept separate from the neutral in the usual way.
With PME. there is a potential danger in that if the combined neutral/earth conductor of the supply became broken (very unlikely but nevertheless possible), the voltage on the earth conductors could rise towards the full supply voltage. It is most important therefore that equipotential bonding is rigorously applied in installations supplied by PME. The minimum size of main bonding conductor is 10 sq mm but may need to be up to 25 sq mm depending on the size of the incoming neutral/earth conductor: the supply company will advise you.
Electricity System Earthing Arrangements
Mains electricity systems are categorised in the UK according to how the earthing is implemented. The common ones are TN-S, TN-C-S and TT. You will sometimes see these referred to in questions and answers about mains wiring.
Note that in these descriptions, 'system' includes both the supply and the installation, and 'live parts' includes the neutral conductor.
First letter:
T The live parts in the system have one or more direct connections to earth.
I The live parts in the system have no connection to earth, or are connected only through a high impedance.
Second letter:
T All exposed conductive parts are connected via your earth conductors to a local ground connection.
N All exposed conductive parts are connected via your earth conductors to the earth provided by the supplier.
Remaining letter(s):
C Combined neutral and protective earth functions (same conductor).
S Separate neutral and protective earth functions (separate conductors).
TN-C No separate earth conductors anywhere - neutral used as earth throughout supply and installation
TN-S Probably most common, with supplier providing a separate earth conductor back to the substation.
TN-C-S [Protective Multiple Earthing] Supply combines neutral and earth, but they are separated out in the installation.
TT No earth provided by supplier; installation requires own earth rod (common with overhead supply lines).
IT Supply is e.g. portable generator with no earth connection, installation supplies own earth rod.
Inside or nearby your consumer unit (fuse box) will be your main earthing terminal where all the earth conductors from your final sub-circuits and service bonding are joined. This is then connected via the 'earthing conductor' to a real earth somehow...
TN-S The earthing conductor is connected to separate earth provided by the electricity supplier. This is most commonly done by having an earthing clamp connected to the sheath of the supply cable.
TN-C-S The earthing conductor is connected to the supplier's neutral. This shows up as the earthing conductor going onto the connection block with the neutral conductor of the supplier's meter tails. Often you will see a label warning about "Protective Multiple Earthing Installation - Do Not Interfere with Earth Connections" but this is not always present.
TT The earthing conductor goes to (one or more) earth rods, one of them possibly via an old Voltage Operated ELCB (which are no longer used on new supplies).
There are probably other arrangements for these systems too. Also, a system may have been converted, e.g. an old TT system might have been converted to TN-S or TN-C-S but the old earth rod was not disconnected.

 

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Consumer Units
Live parts must be contained inside enclosures or behind barriers providing a degree of protection of at least IX2X or IPXXB. 416.2.1
The horizontal top surface of a readily Accessible barrier or enclosure must provide a degree of protection of at least IX4X or IPXXD. 416.2.2
All installations must be divided into separate circuits so as to comply with the following :
- avoid danger and inconvenience if a fault develops
- allow safe maintenance, inspection & testing
- prevent any danger that may be caused by the loss of supply to a single circuit e.g. a lighting circuit
- reduce the possibility of nuisance tripping of RCDs by equipment with high cpc currents produced in normal use e.g. computers
- prevent electromagnetic interference between items of electrical equipment
- prevent the accidental energising of an isolated circuit .
314.1

A double pole main switch or linked circuit breaker must be installed as close as possible to the incoming supply at the origin of the installation. 537.1.4
Unless specifically labelled or suitably identified, all 13A socket outlets must be 30ma RCD protected. 411.3.3
Fire detection circuits must be supplied independently of other circuits and not protected by an RCD protecting multiple circuits. 560.7.1
Fire detection .cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Extra Low Voltage circuits should not be run in the same wiring system as 230v circuits unless all ELV cables and conductors are insulated for 230v or separated by an earthed metal screen. 528.1
All electrical equipment must be accessible for operation, inspection & testing , maintenance and repair. 132.12
Before an installation or an addition / alteration to an installation is energised, inspection and testing must be carried out to ensure the requirements of BS-7671 have been met and an appropriate Certificate must then be issued. 134.2.1, 610.6, 631.1
Any defects found in the existing installation must be recorded on the Electrical Installation Certificate or Minor Electrical Installation Works Certificate. 633.2
A single pole fuse or circuit breaker must be used with the line conductor only. 132.14.1
Only a linked circuit breaker that breaks all related line conductors can be used with an earthed natural conductor. 132.14.2
All final circuits must be connected to a separate way in the consumer unit. 314.4
In a ccu the natural conductors and cpc's should be connected to their respective terminals in the same order as the phase conductors are connected to the mcb's. 514.1.2

An unfused spur may be connected to the origin of a radial or ring final circuit in the consumer unit. 433.1
All protective devices must be labelled. 514.8.1
A periodic inspection notice must be fixed on or next to the ccu. 514.12.1
Where applicable an RCD notice must be fixed on or next to the ccu. 514.12.2
Where the installation contains wiring colours to two versions of BS-7671 a warning notice must be fixed on or next to the ccu. 514.14.1
A voltage warning notice is only required where a nominal voltage exceeding 230v exists. 514.10.1
A durable copy of the schedule from the electrical installation certificate must be fixed next to or placed inside the consumer unit. In addition to circuit details the schedule must also contain information about the protective measures used in the installation ie automatic disconnection of supply, electrical separation , SELV , RCD. 132.13, 514.9
All literature supplied with fire detection equipment must be made available to the occupant of the dwelling. 560.7.12
Fuses and mcb's must have a breaking capacity greater than or equal to the maximum PFC at the point where the device is installed. 432.1 A lower breaking capacity is allowed if another fuse or mcb with the necessary breaking capacity is installed on the supply side and the energy let-through of both devices will not damage the fuse or mcb on the load side. 434.5.1, 536.1
Consumer units must be spaced at least 150mm away from gas pipes unless there is a pane of non combustible insulating material separating them. OSG p18
In areas subject to flooding, consumer units should preferably be installed above flood water level. OSG p161
Overcurrent protection devices must comply with one or more of the following standards :

Bs 88-2.2 .
Bs 88-6 .
Bs 646 .
Bs 1361 .
Bs 1362 .
Bs 3036 .
Bs en 60898-1 & -2 .
Bs en 60947-2 & -3 .
Bs en 60947-4-1, -6-1 & -6-2 .
Bs en 61009-1 .
533.1

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE : p-335 / 336

GUIDANCEFOR RECIPIENTS (to be appended to the Certificate)
This Certificate has been issued to confirm that the electrical installation work to which it relates has been
designed, constructed and inspected and tested in accordance with British Standard 7671, (the IEE Wiring
Regulations). You should have received in ‘original’ Certificate and the contractor should have retained
duplicate. If you were the person ordering the work, but not the owner of the installation, you should
pass this Certificate, or copy of it, to the owner.
A separate Certificate should have been received for each existing circuit on which minor works have been
carried out. This Certificate is not appropriate if you requested the contractor to undertake more extensive
installation work., for which you should have received an Electrical installation Certificate.
The Certificate should be retained in safe place and be shown to any person inspecting or undertaking
further work on the electrical installation in the future. If you later vacate the property, this Certificate
will demonstrate to the new owner that the minor electrical installation work carried out complied with
the requirements of British Standard 7671 at the time the Certificate was issued.

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE :
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 767 ( IEE WIRING REGULATIONS )
To be used only for minor electrical work which does not include the provision of new circuit

Agreed limitations on the inspection and testing ← with Client ,

Declaration
I/We certify that the electrical installation work, as detailed in part 1 of this certificate, do not impair the safety of the existing installation, that the said works have been
designed, constructed, inspected and tested in +accordance with BS 7671:2008 * ( IEE Wiring Regulations), amended to the date shown* and that to the best of my/our
knowledge and belief, the time of my/our inspection, complied with BS 7671 except as detailed in Part 1 of this certificate.
This form is based on the model shown in Appendix 6 of BS 7671: 2008

239- Inspection Testing & Certification of Electrical Installations Exam : Part B scenario :
Solution to terminating the underground SWA supply cable :
-&-'s question may lead you to terminate the SWA of the underground supply cable, since the question informs you. "You are NOT allowed to use the supply companies earthing system as a means of earthing the outhouse" However -&-'s mention nothing about earthing the supply cable itself. It is difficult to decide whether -&-'s are just testing the candidates knowledge of this situation VERY thoroughly or alternatively offering a red-herring to mislead the unwary candidate. Whichever is the reason for this question, it caused many exam candidates a great deal of difficulty and lost time trying to decide what the solution was.

The actual solution stems from BS 7671 regulation 542.1.8 part of this reg states , ←

"If the protective conductor ( i.e. the swa ) forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device" This therefore has to be the main house end. See the only possible solution below :
( Main house CCU / TN-C-S / Systems ) MET : ←←

part B scenario : gave many candidates a difficult time. Here you were presented with a TN-C-S system installed in a domestic property, and an underground supply cable is being used to supply an external outhouse. However the electricity supply company will not allow you to use their means of earthing for the outhouse. So how do you provide a means of earthing for the outhouse? Where do you earth the supply cable? What checks must you make on the underground supply cable? Why can't you use the main house TN-C-S system as a means of earthing the outhouse ?

 

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Many candidates continue to get the value of Zs wrong for the circuit in question in part B of the exam.
A common error when completing questions involving schedule of test results is to forget to indicate functional tests have been performed and found satisfactory/unsatisfactory. To tick the tick box when completing details of ring final circuits, ensuring to indicate continuity of ring final conductors have been performed.
Failure to record the type of earthing system, i.e. TN-S, TN-C-S, TT,
Failure to record the value of Ze, PFC, Nominal voltage, Nominal frequency, are common errors.
Test procedures
A very common question is to explain in detail how to perform an insulation resistance test, often on a lighting circuit. Candidates regularly fail to state the instrument used which is an 'Insulation Resistance Ohm-meter' (Not a Megger! You will not gain any marks if you answer a Megger) Many candidates fail to identify the test voltage required for typical 230/240 volt installation which is 500 volts and the acceptable test value which is 0.5 Meg-ohm or greater (again due to change under 17th edition to a minimum acceptable value of 1.0 Meg-ohm) City and Guilds usually deliberately pick a lighting circuit that is stipulated as having two way switching, just to see if the candidate mentions to test the strappers in BOTH positions.
Failure to mention testing the insulation resistance of both strappers will lose you marks. Be warned!
Candidates regularly make mistakes when answering RCD questions. Often the question or specifications usually given in part B will make reference to a specific type of RCD for example a 30 mA RCD. Candidates are then asked to state the actual test current applicable to test this type of RCD. Candidates regularly incorrectly state the answer as x1/2 x1 and x5 instead of x1/2 = 15mA x1 = 30mA and x5 = 150mA

'Memorandum of Guidance on the Electricity at Work Regulations 1989'
This may help you somewhere on your 2391 ,

5. General :

1. The majority of the regulations are directed at hardware requirements. Installations are required to be of proper construction; conductors must be insulated or other precautions taken; there must be means of cutting off the power and means for electrical isolation. The hardware requirements are complemented by a group of regulations stating principles of safe working practice. Regulation 14, which covers live working, is of particular importance.
2. The scope of the EAW Regulations is limited by the definition of danger and injury solely to risks arising from an electrical source and does not include, for example, control-system faults and consequent hazards such as aberrant machinery behavior.
3. The EAW Regulations revoke a number of specific regulations, but a number remain which either overlap or appear to overlap, for example
1. the Electricity Safety, Quality and Continuity Regulations 2002 (as amended): see the introduction to the Memorandum of guidance.
2. the Low Voltage Electrical Equipment (Safety) Regulations 1988 (made under the Consumer Protection Act 1987);
3. the Building (Scotland) Regulations 2004: these give deemed to satisfy status to BS7671 Requirement for Electrical Installations (also known as the Institution of Electrical Engineers Wiring Regulations, 16 th Edition); and
4. the Cinematographic (Safety) Regulations, 1955.
If demarcation between these sets of regulations and the EAW Regulations is unclear in a particular case, then details should be passed to HSE, via the Enforcement Liaison Officer.
4. Appendices 1 and 2 of the Memorandum of guidance list publications relating to electrical safety.

6. Enforcement
1. There is no expectation that inspectors should change their general approach to enforcement. However, particular attention should be paid to the enforcement of reg 14. (Work on, or near, live conductors).
2. In situations where the 1908 Regulations previously applied or where HSW Act was used, inspectors should now enforce the EAW Regulations.
3. There should be no difference in enforcement between situations in which no specific regulations previously applied and those which were regulated
4. Nothing is required by the EAW Regulations which is not already the norm in the best undertakings.
5. The EAW Regulations will apply to electrical work in domestic premises. Such work will fall to HSE to enforce.
6. Expert assistance to prove the presence of electricity should not be necessary when contemplating enforcement action. Circumstantial evidence should suffice to indicate that electricity is present and that the EAW Regulations apply. Such evidence could include:
1. that the equipment carried a plate indicating that it worked at mains voltage;
2. that the equipment was connected to a supply via a 3-pin plug;
3. that the premises were supplied with electricity for lighting which was working; and
4. that a person on the premises paid an electricity bill.
In court, an expert witness should be able to use such evidence to express a professional opinion as to the dangers which were present or likely to occur.
7. It may also be possible to use an on-site electrician to measure voltages and use his or her measurements in evidence.
8. An improvement notice may be appropriate it conductors are inadequately protected against damage; for example, not routed through conduit, tubing or armouring in premises where the risk of physical damage is apparent. In particularly arduous conditions, e.g. construction work, stronger action may be considered.
9. Exposed and accessible live conductors or a lack of earthing could justify a prohibition notice. Lack of earthing can only be proved by measurement; simple observation is never adequate.

7. Interpretation (Reg 2)
1. The definitions of danger and injury are linked but distinguished to accommodate those circumstances when persons must work on or so near live equipment that there is a risk of injury, ie where danger is present and cannot be prevented.
2. Danger includes danger to the public.
3. The definition of electrical equipment excludes items which only generate electricity adventitiously, eg as static.
4. Earthing and isolation are defined in regs.8 and 12 respectively.
8. Duties (Reg 3)
1. Regulation 3 imposes duties only on employers, employees, the self-employed, and mine or quarry managers. In other cases HSW Act ss.3 and 4 will apply.
2. All duties are limited by the phrase "to matters which are within his control", apart from reg.3(2)(a) which is similar to HSW Act, s.7(b). Some large industries tend to produce written rules which clearly define the extent of an individual's control but it will often be the case that there is overlapping liability where several individuals and/or bodies corporate are duty holders.

9. Systems, work activities and protective equipment (Reg 4)
1. Regulation 4 acts as a catch-all requirement.
2. Due to the broad definition of system (reg 2), reg 4 covers almost every conceivable electrical danger: from an exploding lithium battery in a calculator to the output side of a power station.
3. Systems in vehicles are covered by reg 4, but note should be taken of reg 32 in relation to ships, aircraft and hovercraft.
4. Regulation 4(3) embraces all work which could lead to electrical danger, although such work may not be associated with an electrical system. This would include work in the vicinity of electrical equipment and insulated or uninsulated conductors. The requirement does not limit proximity to conductors, live or dead, but rather regulates the work activity so as not to give rise to danger.
5. Regulation 4(3) is almost always applicable to work on or near underground cables, in which situations the standards of the Construction (GP) Regulations, reg 44 should be maintained, viz electrical isolation by disconnection and secure separation from sources of electrical supply. However, reg 14 should be used if there has been a failure to switch off the supply to such cables before undertaking work. That said, the circumstances of each case will dictate which regulation should be used.
6. The duties in reg 4(4) are not qualified by "so far as is reasonably practicable' and link with reg 14(c) ensuring that protective equipment provided is always suitable for the purpose.
10. Strength and capability of electrical equipment (Reg 5)
1. The assigned rating of electrical equipment represents the extent to which it may be used in an assessment of the adequacy of equipment strength and capability in foreseeable conditions of actual use; but may not necessarily represent all factors to be considered. A technical judgement by a competent person will often be needed to determine adequacy.
2. If a failure has occurred it may be relatively easy to prove a contravention. However, expert support will be required except where a deficiency is obvious and requires no technical proof.

 

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11. Adverse or hazardous environments (Reg 6)
1. Regulation 6 addresses extrinsic effects which are reasonably foreseeable. For example, in order to prove a contravention of reg.6, it is not necessary to show that electrical equipment is or has been exposed to a flammable atmosphere, but only that it is foreseeable that it could be so exposed.
2. The Memorandum of guidance gives general advice on the different hazardous environments covered by reg 6, and makes reference to relevant standards and publications.
12. Insulation, protection and placing of conductors (Reg 8)
1. This regulation is an example of where the EAW Regulations extend protection to anyone exposed to electrical danger from electrical equipment, including those not at work
13. Earthing and other suitable precautions (Reg 8)
1. This regulation applies to any conductor and not just to metal. It also allows other suitable means of preventing danger as an alternative to earthing.
2. The duty to prevent danger arising is activated only when a relevant conductor becomes charged.
3. Regulation 4 requires that systems are constructed so as to prevent danger; but in the event that danger arises because a conductor which should be earthed is not, reg.8 also becomes relevant.
4. As regards adequate earthing, the use of a conductor with a small cross-sectional area, which is not capable of carrying a heavy current for the duration of the fault, is not acceptable.
5. Inspectors should continue to press for the use of reduced voltage lighting and power tools, e.g. 110v centre tapped to earth in the working environments described in para 19 of the Memorandum of Guidance (e.g. construction work).

14. Integrity of reference conductors (Reg 9)
1. Regulation 9 is fully explained in the Memorandum of guidance.
15. Connections (Reg 10)
1. The definition of danger means that connections have to be mechanically and electrically suitable to prevent the risk of electrical injury.
16. Means for protecting from excess current (Reg 11)
1. The due-diligence defence in reg 29 is important when enforcing this requirement because, in theory, it is impossible in an absolute sense to prevent danger arising before any excess current protection device operates.
17. Means of cutting off the supply and for isolation (Reg 12)
1. This regulation cannot be used to require means to prevent non-electrical hazards arising from the use of electrical controlled systems.
2. Permit-to-work systems relying on a warning notice may be encountered. Where such systems are well established, tried and tested they could represent adequate isolation. However, they need to meet the minimum requirements of this regulation and when assessing such systems, inspectors should seek expert assistance, where appropriate.
3. Regulation 12 covers electrical equipment which may become charged by means other than connection to the supply, e.g. through capacitance or induced current arising from proximity to other live conductors.
4. There are no voltage limits.
18. Precautions for work on equipment made dead (Reg 13)
1. Regulation 13 may apply during any work, be it electrical or non-electrical.

19. Work on or near live conductors (Reg 14)
1. This regulation is very important and should be used to reduce the incidence of live working and to ensure strict precautions are adhered to when such work is carried out.
2. All 3 conditions stipulated in the regulation must be met before live working is permitted.
3. "Reasonable in all the circumstances" (reg 14(b)) means that all necessary precautions must be taken to ensure it is reasonable for someone to be asked to work.
4. Regulation 14(c) could imply that in the absence of injury no precautions can be required in advance. This would mean that notices requiring such precautions could not be issued. This interpretation is not correct because:
1. it would not be reasonable to work in a situation where the necessary precautions had not been taken; and
2. in order to take precautions it is necessary to foresee the potential harm, and such precautions will only be suitable if they are adequate to prevent the harm foreseen.
Therefore, if an inspector judges that the precautions taken will not prevent injury, he or she could issue a notice citing an apparent breach of reg 14.
5. Inspectors should question all live working wherever they find it. This could be in many establishments and also where peripatetic electricians are working.
6. The issue of accompaniment during live work is touched upon in the Memorandum of guidance. The presence of a colleague who could render assistance if safe to do so could prevent injury or mitigate its extent.
20. Working space, access and lighting (Reg 15)
1. This regulation only applies to the period during which work is being carried out.
2. It can be used to prevent the storage of goods etc in front of switchboards on the basis that the act of operating switching device is considered to constitute work on the equipment in question.

21. Competence to prevent danger and injury (Reg 16)
1. If competence is in doubt, inspectors should enquire into:
1. technical knowledge, and
2. experience
in relation to the work activity being undertaken. Clearly, more knowledge is required of those involved in high voltage work compared to those doing 25-volt test work.
2. HSE specialist support is available for assessing electrical competence (via the ELO).
3. The regulation does not require authorisation of competent persons but in conjunction with regs 4 and 14 such authorisation may be required, when necessary, to avoid danger.
4. The regulation does not specify any age limitations. The key requirements are adequate and relevant knowledge and experience, or an appropriate degree of supervision to allow persons to work safely and possibly to acquire those attributes.
22. Defence (Reg 29)
1. The defence only becomes relevant once it has been established that an offence has been committed. It should not affect the judgement of the duty holder as to the steps he or she should take to meet an absolute requirement
2. Employers may suggest that they have taken reasonable steps to meet their obligations by the delegation of responsibility to adequately qualified and instructed staff. This approach is pre-empted by the specific duties placed upon employers and others by reg 3.
3. HSE electrical specialists may be able to provide technical support in relation to a due diligence defence.

23. Exemptions (Reg 30)
1. Any applications for an exemption should be forwarded, together with a full report, to the Local Authority Unit.
24. Disapplication of duties (Reg 32)
1. The EAW Regulations apply to all vehicles, except those exempted by this regulation
2. Sea-going ships are exempt in relation to normal shipboard activities under the direction of the Master, whether they are in dock or under way in an inland waterway or at sea.
3. The term sea-going is not defined in these or any other health and safety regulations, but the intended meaning is clear and common to other regulations (eg Docks, COSHH).
4. The reference to any person in reg 32(b) includes the employer.

Appendix
Key issues on which the EAW Regulations And Electricity (Factories Act) Special Regulations 1908 And 1944 (Plus Exemptions) differ
1. Appendix 3 of the Memorandum of guidance gives information on reg 17 of the old regulations in relation to the new provisions. The minimum dimensions for switchboard passage-ways are given tacit approval.
2. Regulation 14 of the EAW Regulations covers all live working not just work on switchboards above 650 volts.
3. There is no specific requirement under the EAW Regulations for the display-of an electric shock placard or an abstract of the 1908/1944 Regulations. Occupiers should be told to remove abstracts but advised to retain placards where these are appropriate (see page 32, para 23 of Memorandum). There is no objection to occupiers displaying the new regulations in placard form if they desire.
4. There are no voltage bandings in the EAW Regulations.
5. There are differences in definitions between old and new. In particular conductor and danger have different meanings in the EAW Regulations.
6. Regulation 5 of the EAW Regulations corresponds to reg 1 of 1908 but is confined to the prevention of electrical danger. It does not cover machine malfunctions from electrical faults. All at risk are covered by reg 5, not just employees.
7. Under reg 6 of the EAW Regulations (as opposed to reg 27 of 1908) it is no longer necessary to show that equipment is or has been exposed to a flammable atmosphere. A foreseeable exposure will suffice.
8. Regulation 8 of the EAW Regulations applies to all conductors, unlike reg 21 of 1908 which only applied to exposed metalwork.
9. Regulation 13 of 1908 required the earthing of mobile generators. Under the EAW Regulations, reg 8 permits alternative approaches where earthing is not practicable.
10. The EAW Regulations contain no specific requirement for the written authorisation of competent persons, although authorisation may be required when necessary to avoid danger.

 

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Electrical Safety and you : ( HSE )
INTRODUCTION :
Electricity can kill. Each year about 1000 accidents at work involving electric shock
or burns are reported to the Health and Safety Executive (HSE). Around 30 of
these are fatal. Most of these fatalities arise from contact with overhead or
underground power cables.
Even non-fatal shocks can cause severe and permanent injury. Shocks from faulty
equipment may lead to falls from ladders, scaffolds or other work platforms.
Those using electricity may not be the only ones at risk: poor electrical
installations and faulty electrical appliances can lead to fires which may also cause
death or injury to others. Most of these accidents can be avoided by careful
planning and straightforward precautions.
This leaflet outlines basic measures to help you control the risks from your use of
electricity at work. More detailed guidance for particular industries or subjects is
listed on pages 6 - 8. If in doubt about safety matters or your legal responsibilities,
contact your local inspector of health and safety. The telephone number of your
local HSE office will be in the phone book under Health and Safety Executive. For
premises inspected by local authorities the contact point is likely to be the
environmental health department at your local council.
WHAT ARE THE HAZARDS ?
The main hazards are:
■ contact with live parts causing shock and burns (normal mains voltage,
230 volts AC, can kill);
■ faults which could cause fires;
■ fire or explosion where electricity could be the source of ignition in a
potentially flammable or explosive atmosphere, e.g. in a spray paint booth.
ASSESSING THE RISK :
Hazard means anything which can cause harm. Risk is the chance, great or small, that someone will actually be harmed by the hazard.
The first stage in controlling risk is to carry out a risk assessment in order to
identify what needs to be done. (This is a legal requirement for all risks at work.)
When carrying out a risk assessment:
■ identify the hazards;
■ decide who might be harmed, and how;
■ evaluate the risks arising from the hazards and decide whether existing
precautions are adequate or more should be taken;
■ if you have five or more employees, record any significant findings;
■ review your assessment from time to time and revise it if necessary.
The risk of injury from electricity is strongly linked to where and how it is used.
The risks are greatest in harsh conditions, for example:
■ in wet surroundings - unsuitable equipment can easily become live and
can make its surroundings live;
■ out of doors - equipment may not only become wet but may be at
greater risk of damage;
■ in cramped spaces with a lot of earthed metalwork, such as inside a tank
or bin - if an electrical fault developed it could be very difficult to avoid
a shock.
Some items of equipment can also involve greater risk than others. Extension
leads are particularly liable to damage - to their plugs and sockets, to their
electrical connections, and to the cable itself. Other flexible leads, particularly
those connected to equipment which is moved a great deal, can suffer from
similar problems.

REDUCING THE RISK
Once you have completed the risk assessment, you can use your findings to
reduce unacceptable risks from the electrical equipment in your place of work.
There are many things you can do to achieve this; here are some.
Ensure that the electrical installation is safe
■ install new electrical systems to a suitable standard, e.g. BS 7671 Requirements
for electrical installations, and then maintain them in a safe condition;
■ existing installations should also be properly maintained;
■ provide enough socket-outlets - overloading socket-outlets by using
adaptors can cause fires.
Provide safe and suitable equipment
■ choose equipment that is suitable for its working environment;
■ electrical risks can sometimes be eliminated by using air, hydraulic or hand powered
tools. These are especially useful in harsh conditions;
■ ensure that equipment is safe when supplied and then maintain it in a safe
condition;
■ provide an accessible and clearly identified switch near each fixed machine
to cut off power in an emergency;
■ for portable equipment, use socket-outlets which are close by so that
equipment can be easily disconnected in an emergency;
■ the ends of flexible cables should always have the outer sheath of the cable
firmly clamped to stop the wires (particularly the earth) pulling out of the
terminals;
■ replace damaged sections of cable completely;
■ use proper connectors or cable couplers to join lengths of cable. Do not
use strip connector blocks covered in insulating tape;
■ some types of equipment are double insulated. These are often marked with
a ‘double-square’ symbol . The supply leads have only two wires - live
(brown) and neutral (blue). Make sure they are properly connected if the
plug is not a moulded-on type;
■ protect light bulbs and other equipment which could easily be damaged in
use. There is a risk of electric shock if they are broken;
■ electrical equipment used in flammable/explosive atmospheres should be
designed to stop it from causing ignition. You may need specialist advice.
Reduce the voltage
One of the best ways of reducing the risk of injury when using electrical equipment
is to limit the supply voltage to the lowest needed to get the job done, such as:
■ temporary lighting can be run at lower voltages, eg 12, 25, 50 or 110 volts;
■ where electrically powered tools are used, battery operated are safest;
■ portable tools are readily available which are designed to be run from a
110 volts centre-tapped-to-earth supply.
Provide a safety device
If equipment operating at 230 volts or higher is used, an RCD (residual current
device) can provide additional safety. An RCD is a device which detects some, but
not all, faults in the electrical system and rapidly switches off the supply. The best
place for an RCD is built into the main switchboard or the socket-outlet, as this
means that the supply cables are permanently protected. If this is not possible a
plug incorporating an RCD, or a plug-in RCD adaptor, can also provide additional safety.

RCDs for protecting people have a rated tripping current (sensitivity) of not more
than 30 milliamps (mA). Remember:
■ an RCD is a valuable safety device, never bypass it;
■ if the RCD trips, it is a sign there is a fault. Check the system before using it
again;
■ if the RCD trips frequently and no fault can be found in the system, consult
the manufacturer of the RCD;
■ the RCD has a test button to check that its mechanism is free and
functioning. Use this regularly.
Carry out preventative maintenance
All electrical equipment and installations should be maintained to prevent danger.
It is strongly recommended that this includes an appropriate system of visual
inspection and, where necessary, testing. By concentrating on a simple, inexpensive
system of looking for visible signs of damage or faults, most of the electrical risks
can be controlled. This will need to be backed up by testing as necessary.
It is recommended that fixed installations are inspected and tested periodically by
a competent person.
The frequency of inspections and any necessary testing will depend on the type of
equipment, how often it is used, and the environment in which it is used. Records
of the results of inspection and testing can be useful in assessing the effectiveness
of the system.
Equipment users can help by reporting any damage or defects they find.
Work safely
Make sure that people who are working with electricity are competent to do the
job. Even simple tasks such as wiring a plug can lead to danger - ensure that people
know what they are doing before they start.
Check that:
■ suspect or faulty equipment is taken out of use, labelled ‘DO NOT USE’ and
kept secure until examined by a competent person;
■ where possible, tools and power socket-outlets are switched off before
plugging in or unplugging;
■ equipment is switched off and/or unplugged before cleaning or making
adjustments.
More complicated tasks, such as equipment repairs or alterations to an electrical
installation, should only be tackled by people with a knowledge of the risks and the
precautions needed.
You must not allow work on or near exposed live parts of equipment unless it is
absolutely unavoidable and suitable precautions have been taken to prevent injury,
both to the workers and to anyone else who may be in the area.
Underground power cables
Always assume cables will be present when digging in the street, pavement or near
buildings. Use up-to-date service plans, cable avoidance tools and safe digging
practice to avoid danger. Service plans should be available from regional electricity
companies, local authorities, highways authorities, etc.
Overhead power lines
When working near overhead lines, it may be possible to have them switched off if the owners are given enough notice. If this cannot be done, consult the owners

about the safe working distance from the cables. Remember that electricity can
flash over from overhead lines even though plant and equipment do not touch
them. Over half of the fatal electrical accidents each year are caused by contact
with overhead lines.

Mac : can you put the ( HSE ) stuff in the Doc , Useful Information for Apprentices , please Sorry about that . Amberleaf

 

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Definitions : Earth Fault Current :
A Fault Current which flows to Earth ,

Earth Fault Loop Impedance :
The Impedance of the Earth Fault Current Loop starting and ending at the point of the Earth Fault .
This Impedance is denoted by ( Zs )
The Earth Fault Loop comprises the following , starting at the point of Fault :
* the Circuit Protective Conductor ,
* the Consumers Earthing terminal and Earthing Conductor ,
* for TN-Systems , the return path ,
* for TT and IT Systems , the Earth return path ,
* the path through the Earthed Neutral point of the Supply Transformer and the Transformer Winding ,
* the Phase Conductor from the Transformer Supply to the point of Fault ,

BS 7671:2008
(i) The Electrical Installation Certificate required by part 6 : should be made out and signed or otherwise
authenticated by a competent person or persons in respect of the design, construction, inspection and testing of the work

(ii) The Minor Works Certificate required by Part 6 : should be made out and signed or otherwise authenticated by
a competent person in respect of the design, construction, inspection and testing of the minor work.
(iii) The Periodic Inspection Report required by part 6 : should be made out and signed or otherwise authenticated
by a competent person in respect of the inspection and testing of an installation
(iv) Competent persons will, as appropriate to their function under (i) (ii) and (iii) above, have a sound
knowledge and experience relevant to the nature of the work undertaken and to the technical standards set
down in these Regulations, be fully versed in the inspection and testing procedures contained in these
Regulations and employ adequate testing equipment
(v) Electrical Installation Certificates will indicate the responsibility for design, construction, inspection and
testing, whether in relation to new work or further work on an existing installation .
Where design, construction, inspection and testing are the responsibility of one person a Certificate with a
single signature declaration in the form shown below may replace the multiple signatures section of the model form

FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING
I being the person responsible for the Design, Construction, Inspection & Testing of the electrical
installation (as indicated by my signature below), particulars of which are described above, having
exercised reasonable skill and care when carrying out the Design, Construction, Inspection & Testing,
hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge
and belief in accordance with BS 7671 :2008, amended to .............(date) except for the departures, if
any, detailed as follows.
(vi) A Minor Works Certificate will indicate the responsibility for design, construction, inspection and testing of
the work described on the certificate.
(vii) A Periodic Inspection Report will indicate the responsibility for the inspection and testing of an installation
within the extent and limitations specified on the report.
(viii) A Schedule of Inspections and a Schedule of Test Results as required by part 6: should be issued with the
associated Electrical Installation Certificate or Periodic Inspection Report.
(ix) When making out and signing a form on behalf of a company or other business entity, individuals should
state for whom they are acting.
(x) Additional forms may be required as clarification, if needed by ordinary persons, or in expansion, for larger
or more complex installations.
(xi) The IEE Guidance Note 3 provides further information on inspection and testing on completion and for
periodic inspections ,
ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2
1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or
for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used.
For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical
Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1 A duplicate
should be retained by the contractor.
2. This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test
Results.
3. The signatures appended are those of the persons authorized by the companies executing the work of
design, construction, inspection and testing respectively. A signatory authorized to certify more than
one category of work should sign in each of the appropriate places.
4. The time interval recommended before the first periodic inspection must be inserted (see IEE Guidance
Note 3 for guidance).
5. The page numbers for each of the Schedules of Test Results should be indicated, together with the total
number of sheets involved.
6. The maximum prospective fault current recorded should be the greater of either the short-circuit current or
the earth fault current.
7. The proposed date for the next inspection should take into consideration the frequency and quality of
maintenance that the installation can reasonably be expected to receive during its intended life, and the
period should be agreed between the designer, installer and other relevant parties

 

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FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING :

I being the person responsible for the Design, Construction, Inspection & Testing of the electrical
installation (as indicated by my signature below), particulars of which are described above, having
exercised reasonable skill and care when carrying out the Design, Construction, Inspection & Testing,
hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge
and belief in accordance with BS-7671:2008 , amended to .............(date) except for the departures, if any, detailed as follows ,

(vi) A Minor Works Certificate will indicate the responsibility for design, construction, inspection and testing of
the work described on the certificate.
(vii) A Periodic Inspection Report will indicate the responsibility for the inspection and testing of an installation
within the extent and limitations specified on the report.
(viii) A Schedule of Inspections and a Schedule of Test Results as required by part 6 should be issued with the
associated Electrical Installation Certificate or Periodic Inspection Report.
(ix) When making out and signing a form on behalf of a company or other business entity, individuals should
state for whom they are acting.
(x) Additional forms may be required as clarification, if needed by ordinary persons, or in expansion, for large
or more complex installations.
(xi) The IEE Guidance Note 3 provides further information on inspection and testing on completion and for periodic inspections ,

ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2 :
1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or
for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used.
For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical
Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1 . A duplicate
should be retained by the contractor.
2. This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test
Results.
3. The signatures appended are those of the persons authorized by the companies executing the work of
design, construction, inspection and testing respectively. A signatory authorized to certify more than
one category of work should sign in each of the appropriate places.
4. The time interval recommended before the first periodic inspection must be inserted (see IEE
Note 3 for guidance).
5. The page numbers for each of the Schedules of Test Results should be indicated, together with the total
number of sheets involved.
6. The maximum prospective fault current recorded should be the greater of either the short-circuit current or
the earth fault current.
7. The proposed date for the next inspection should take into consideration the frequency and quality of
maintenance that the installation can reasonably be expected to receive during its intended life, and the
period should be agreed between the designer, installer and other relevant parties

SCHEDULES (note 2)
The attached Schedules are part of this document and this Certificate is valid only when they are attached to it.
............ Schedules of Inspections and ............ Schedules of Test Results are attached
(Enter quantities of schedules attached)

GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with
British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the
installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate
the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate
was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is
included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next
inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration or to an existing installation. It should not
have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such an inspection ,
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended ,

Excess earth leakage
The RCDs operating principle is to measure the current imbalance between that flowing into and out of a circuit down live and neutral wires. In an ideal world the current difference would be zero, however in the real world there are a various different types of equipment that will legitimately have a small amount of leakage to earth, even operating normally. If the RCD is protecting too many such devices then it is possible that the cumulative result of all these small leakages will be enough to either
• trip the RCD
• or by passing most of the RCD's trip threshold current, make the RCD excessively sensitive to any additional leakage currents
Appliances that typically exhibit high leakage currents
Dampness : Any device that handles water and electricity will be vulnerable to dampness getting into electrical connections or wiring harnesses. This can result in short term high levels of leakage that mysteriously vanish later (as the affected item dries out). Even condensation forming in equipment can cause this problem.

Split water heater elements. These cause gross earth leakage, and conduct it directly through the water being heated. Contrary to what we were taught about electricity and water in primary school, this does not cause electrocution in practice. Split elements can however cause overcurrent leading to overheating of electrical accessories.

DC Resistance tests :
First ensure that power is switched off at the main switch. Ensure all appliances are disconnected from the circuit. These tests require that you disconnect the circuit under test from the consumer unit. In the case of a Ring circuit remember to disconnect both legs of the ring. All tests are initially performed on the disconnected ends of the circuit.
There are a number of basic tests that you can do that will identify a great many of the fixed wiring faults that can cause nuisance tripping.
Test :
Live / Neutral Resistance

Purpose :
The first test is a simple resistance test between live and neutral. This test should be done using the highest resistance range on your multimeter. Normally with all the appliances disconnected you would expect to see an open circuit between live and neutral. If this is not the case then you either have something still connected, or you have a serious insulation resistance problem.

Live Earth Resistance :
This test should also indicate an open circuit with the multimeter on its highest resistance measuring range. Any non infinite reading here could be a direct indication of your problem. If you get a non infinite resistance reading, you may be able to track down the location of the fault by breaking the circuit up at strategic points ( typically by disconnecting part of it at an accessory position ).
Again this test ought to indicate infinite resistance. However it is possible that a very low resistance measurement could exist and yet the circuit still work some of the time (especially on systems with TN-C-S Earthing ). Unlike a low resistance reading on a Live to Earth test, this fault would not immediately trip a MCB or blow a fuse .
Neutral Earth Resistance :
Tracing the location of the short or bridge can again be done using the segmenting procedure described above, and also by careful low resistance measurements made in conjunction with expected cable resistances (or see the table in the IEE Wiring Regulations On Site Guide ).
A typical cause of this type of fault, is where a concealed cable has been damaged by a fastening being driven through it. (so if any shelves or pictures have been hung recently, there is a good place to start looking).

 

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What is a TT Earth and why would I want one ?
If you refer to the Earthing Types article you will see there are a number of ways that an earth can be provided for an electrical installation Of the available types TN-S and TN-C-S, where your electricity supplier also provide an earth, are by far the most common. The next most common category is the TT type. You will encounter this situation where the electricity supplier does not provide any connection to allow the installation to be earthed, or you are working on an electrical installation in an outbuilding where it was not appropriate to export the main earth . In either of these cases you are responsible for providing your own earth connection.
Since a TT earthing system will safeguard both lives and equipment it is important that a correctly designed system is installed. It should have:
* Low enough electrical resistance to earth to ensure correct operation of the circuit earth fault protection device ( typically a RCD ).
* Good repeatability (i.e. it should be able to carry fault currents repeatedly, and its performance should remain in spec all year round, irrespective of varying soil conditions)
* High resistance to corrosion ,
* Long life expectancy ,
Types of earth electrode :
The usual way to provide an earth is to place an electrode into the soil. There are a number of ways of doing this, and how well each of them will work will depend to a large extent on the local soil conditions.
Earth Rods or Spikes :
Earth rods are commonly used since they are easy to retrofit to properties and also work well for a relatively small overall rod area. A typical earth rod is 1.2m long and something like 9 to 14mm in diameter, and usually made from copper clad steel, solid copper, or sometimes stainless steel. This is driven into the ground and an electrical connection made to the top of it via an earth clamp. If the resistance achieved with one rod is too high, then most rods have a threaded section that will allow an additional one to be connected to it, and then that too driven into the ground. (Note that the overall length of the electrode has far more effect on the resistance than the diameter).
The connection to the earth rod should be protected with a suitable enclosure, and this must feature a warning label stating that "this is a safety electrical connection and should not be removed."
Driving an earth rod
The usual solution to this is to hit it with a hammer, and keep doing so until it is nearly all gone. However a modern and much simpler equivalent is to use a SDS drill set to hammer only (i.e. rotation stop) mode, fitted with a square drive adaptor and a socket. The socket will keep the drill centered on the spike and should allow you to "power drive" it into the soil.
For many rod sizes you may also obtain a "driving head". This is a cover that will protect the top end of the rod from damage while driving, which will be important if you need to attach and drive further rods to the first one.
You should choose a section of ground that is away from other service pipes and drains, and preferably is comprised of ordinary soil rather than builders rubble. This will not only make driving the spike easier, but will get a lower resistance electrode as a result.
If the spike hits something immovable and will not drive any further you may be able to pull it out and try elsewhere, or if you managed to drive mostly home before it stopping then it may be worth testing as is and cutting off the excess if the result is good enough. If one rod position on its own is not good enough then additional rods can be driven in other locations and "paralleled up" to lower the overall resistance.
It is wise to try an keep a few meters away from other rods so as not to overlap their resistance area (how far, will depend on how good a conductor the local soil is. The poorer it is the closer they can be together).

Earth Plates :
These are typically either solid copper plates, or lattice like plates made from copper rods. These need to be buried in suitable ground. They can not be "driven" later, and require excavation of soil to fit.
Alternative earth types :
Alternative systems are sometimes used such as earth tapes or wires that are run through long channels dug in the ground. Again difficult to retrofit, and not suitable for soils that require deep penetration to reach permanently damp and frost free conditions. There is also an earthing system constructed using the foundation slab of some building types called an Ufer Earthing
Quality of earth :
The quality of the earth obtained will depend to a large extent on the soil moisture content. Soils that stay damp all year round (like heavy clay) will often perform well in this context. You may need more than one rods length to reach the permanently damp soil.
Different soil types will affect the performance. Marshy ground will perform best, with loam, clay, peat and often chalk also working well when damp. Dry sand and rocky ground however can be much harder to get good results with.
Pay attention to temperature range as well. Frozen ground can be ten times less effective than warmer soil.
Soils with high mineral salt content in their moisture will usually perform noticeably better than "ordinary" damp soil.
Testing the electrode resistance :

The aim of the exercise is to achieve a reasonably low resistance path to earth. Usually with this type of earth it is unrealistic to expect to achieve a resistance as low as that you would get from a supplier provided earth (i.e. under 1 ohm), however it is usually easy to achieve a resistance well under 100 ohms, which when combined with a RCD will offer adequate protection.
When testing the resistance of an earth electrode it is important that any parallel connections to earth (such as main equipotential bonds to water or gas mains) are disconnected when the reading is taken. Note that this in itself raises a danger since some of the buildings equipotential zone will be disconnected, and any other occupants of the premises should be warned.
Without specialist test gear :
Anyone with a bit of electrical common sense, knowledge of Ohm's law, and a decent multimeter can measure earth electrode resistance quite easily. You need to isolate the electrode in question and then find a way of getting some current to flow into it. A safe way to do this is to use a double-wound mains transformer with a secondary voltage of around 24V (exact value not critical).
Exactly how you wire this up will depend on the circumstances. If you have a TN system installation where you are adding an earth electrode for an outbuilding etc, then you can make use of your existing supplier provided earthing point as a return path: Connect one end of the secondary via a suitable length of wire to the main earth terminal in the house and connect the other end to your earth electrode via an ammeter.
Energise the primary of the transformer, and the secondary current which flows will immediately give you a rough idea of the total resistance in the circuit, most of which will be attributable to your electrode. For a more accurate result, drive a second temporary earth electrode (a 2ft offcut of 15mm water pipe will do) into the ground at a distance of 10m or more from the one you're measuring. Then use the meter on volts to measure the voltage drop between the two electrodes. Dividing this figure by the electrode current measured earlier gives you the earth resistance. (Reactance in the circuit will be negligible.) Move the temporary reference electrode to a second position and repeat. Average the two values obtained, but if they are significantly different, try further positions for the reference electrode.
If your whole installation is TT system to start with, and you need to measure the impedance of the main or a secondary electrode, then you will need to use another temporary earth connection as a return path. bash a bit of copper water pipe (or similar) into the ground as far away from the electrode under test as you can manage, and use that to complete the circuit. With this technique you must use the separate sensing electrode (a 2nd temporary rod) to establish a voltage reference. Put this one roughly half-way between the other two, and take measurements with it in two or three different places to check that the resistance areas aren't overlapping too much.

 

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This could mean the difference between life and death. Apprentice :
We need to remember the following :-

1. When properly connected an electric current flows through the live wire on its way to the appliance and returns to ground via the neutral wire.
2. If for some reason the current “leaks” ( through dampness, frayed wiring, faulty connections etc ) the current will take the most direct path to earth – often through a person’s body. In this situation if the power is not disconnected instantly then there is a strong possibility that the person will die.
3. The path taken by the current also contributes to the severity of the electric shock. An electric shock which flows from the hand through the arms and to the chest will affect the breathing and heartbeat.
4. The greatest contributing factor to the severity of an electric shock is the exposure time to the current. An RCD cuts off the power in less than the time of a single heartbeat.
An RCD can be tested in two ways :-
1. A push button test – this requires no test instrument.
2. By the use of an RCD Tester – an RCD Tester is designed to check the trip current and trip time. Most RCD Testers can measure from 1 millisecond to 2000 milliseconds .
Many RCD Testers will be capable of conducting both an AC and DC test, Note :
The Standard BS-7671requires that RCDs are tested for trip times at specified intervals i.e. not just a push button test. An RCD Tester is required for this tripping time test.
Earth Testing :
Legally it is a requirement – but is it really necessary ?
Potentially the most dangerous appliances are Class I appliances (earthed appliances) e.g. floor polishers and the like, but also in this category are extension leads.

Class I appliances are designed to have an earth – this means that in the example of the floor polisher the body of the polisher is connected to earth - literally to the ground via an earth conductor which goes right back to the building switchboard and then into the ground the building is sitting on.

If this conductor is damaged anywhere then the consequences can be fatal – I will explain this point in greater detail shortly. It is obvious therefore that the conductor needs to be tested.

Insulation Resistance & Leakage Testing
Insulation resistance tests MUST NOT be carried out using ohmmeters or multimeters because these meters only produce a small battery voltage in the region of 1.5 to 9 volts. This small voltage is insufficient to pressure test the insulation to expose any weakness in it and therefore is totally inappropriate for insulation resistance tests.

Insulation resistance testers and PATs on the other hand are specifically designed to produce 500 volts (or even greater voltage values for some applications) which places the insulation under stress. This test will indicate any weakness that may break down under normal use on the 230 volt supply.

It is a requirement that the resistance measured by the insulation tester in this way should be not less than 1 megohm (1,000,000 ohms) for an electrical appliance to pass this test.

A practical example showing how a multimeter or ohmmeter is inappropriate to test the insulation resistance of an electrical appliance is detailed by the following example:

A 230-volt floor polisher has a partial insulation breakdown between the motor windings and the earthed metal case. The polisher when in use and at its normal operating temperature, causes the sub-circuit protective fuse to blow as a result of the insulation breaking down to the earthed metal frame.
The polisher, when tested with an ohmmeter or multimeter, does not indicate the presence of a fault, as the meter voltages are so low that they do not stress the insulation and therefore do not reproduce the breakdown that occurs when the appliance is in use.
However, testing the same polisher with an insulation resistance tester producing an output of 500 volts causes the insulation to break down under test, thereby indicating a low insulation resistance value and the presence of a fault path.
NOTE The importance of a sound low resistance earth continuity conductor is paramount to the safety of any electrical appliance that requires an Earth. A test as described above would not achieve anything if the integrity of the Earth were not first proven to be in good condition. Should the appliance have an open circuit Earth continuity conductor, it would produce a high resistance test result, but in fact when the appliance was plugged in it would enliven the case and expose a potential shock hazard.

APRENTICE : ELECTRICAL RING MAIN OR RADIAL CIRCUIT :
A ring main is exactly what it says on the tin. It is a ring of wires, circling your home, carrying the mains electricity to sockets on the way. It gets the power from the Consumer Unit and delivers it to the sockets. As both ends of the ring are connected to the same terminals at the consumer unit, the current runs in both directions imposing less of a load on the cables. Electricity loses power over long lengths of cable and trying to put too much power through a cable which is not designed for it, is dangerous, so a ring main delivers power from both ends to keep the load as light as possible.
A radial circuit is a mains power circuit found in some homes to feed sockets and lighting points. It is simply a length of appropriately rated cable feeding one power point then going on to the next. The circuit terminates with the last point on it. It does not return to the Consumer Unit or fuse box as does the more popular circuit, the Ring Mains. To see the wiring at the back of the socket please go to the ring main project.
There is no limit to the number of sockets used on a radial circuit providing the circuit is contained within an area not exceeding 50 square m, and, just like a ring main, spurs, or extra sockets, can be added. The number of spurs must not exceed the number of existing sockets. Regs , p-363
A separate ring main is usually installed on every floor of the house to make sure things are kept safe and it is only when, for example, a spur (additional socket) is added on an upstairs ring main, to feed a socket or light on a downstairs circuit, that things can get tricky. Please read Part P Building Regulations / Regs , 314.4
A ring main uses 2.5mm cable comprising of a live, neutral and earth. This is called two core & earth cable. The 2.5mm is the measurement of the cross sectional area of the cables.
The floor area a ring main serves is also governed. This is because the regulation people have some idea of how much power and lighting we can expect to use in such an area. The maximum area for a ring main is 100 square meters. An average house has a footprint of about 64-70 square meters so this allows for the continuation of the ring into a porch or garage etc. The ring main must be protected by a 32amp MCB.
The cable itself can be up to 60 meters long if it is protected by a cartridge fuse and 50 meters long if protected by an MCB.
There is no limit to the number of sockets you can have on a ring main but there is a limit to the number of spurs you can have from those sockets or from the wiring between them. on adding an extra socket. You can also extend the ring main if you need to.
Units or appliances which use a lot of power, like cookers and showers must be installed on their own circuits so please check the appliances you are considering using on your ring main. It is also a regulation that any socket which is capable of being used to supply power outside of the house is protected by an RCD.,

Apprentice : An MCB is a form of fuse (protective device) which overcomes the traditional problem associated with fuses in so much as when one blows it does not need to be replaced as a fuse does. MCB's operate when they sense an overload, or over current, and become an automatic switch, turning off, or tripping, the MCB when it detects such an overload.
An RCD is a similar protective device which is different in two ways. Firstly it is connected to both the live and neutral wires in the consumer unit making it a double pole switch, whereas the MCB is only connected to the live side of the circuit. Secondly, rather than just detecting an overload of current, it detects the fault which causes the overload.
Many consumer units these days are produced to be split load consumer units. See our project on consumer units. Those circuits which need more protection than others, i.e. showers, sockets serving outdoor appliances, external 230V lighting, must be protected by an RCD. Other circuits such as lighting and cookers, are protected by MCB's.
Each individual circuit, of whatever kind, is protected by an MCB. The circuits needing most protection are also served by 1 RCD. Each circuit does not need its own RCD in a split load board.
If you wanted to protect every circuit against overload and faults, you can install an RCBO which is a residual circuit breaker with over current protection. This is a combined MCB and RCD.
Other forms of fuse are either re-wireable fuses and cartridge fuses. Cartridge fuses are simply fuse wire contained in an enclosed glass or ceramic tube (such as the fuse in a plug) and re-wireable fuses (slowly becoming obsolete as wiring regulations are upgraded) which are simply two terminals connected by a length of accessible fuse wire of differing amperage rating.

 

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The Rules and Regulations Explained :
Regulation 411.3.3.
States that additional protection by means of a 30mA RCD
is to be provided for all socket outlets with a rated current
not exceeding 20A for use by ordinary persons. The only
exceptions allowed are for socket outlets for use under the
supervision of “skilled” or “instructed persons” e.g. some
commercial / industrial locations, or a specific labelled
socket provided for connection of a particular item of equipment, e.g. a freezer circuit.

Regulation 701.411.3.3
In specific locations such as those containing a bath or
shower there is a requirement now to provide RCD
protection on all circuits, including the lighting and shower circuits.

Regulation 314.1 & 2
Requires that every installation shall be divided into
circuits as necessary to avoid danger and minimise
inconvenience, in the event of a fault. Also reducing the
possibility of unwanted RCD tripping, due to excessive
protective conductor currents but not due to an Earth fault.
Separate circuits may be required for parts of the
installation, which need to be separately controlled in such
a way that they are not affected by the failure of other
circuits. The appropriate subdivision should take account
of any danger arising from the failure of a single circuit eg.
an RCD trip on a socket outlet causing the unwanted failure
of a lighting circuit and its associated hazards.

Regulation 522.6.7
Now requires a much greater use of RCD’s to
protect the wiring concealed in walls or partitions even
where installed in previously defined “Safe Zones”.
These regulations effectively mean that all concealed
wiring at a depth of less than 50mm from the surface now
requires protection by a 30mA RCD unless
provided with earthed mechanical protection

The 17th Edition of the IEE wiring regulations ( BS7671 ),
detail a number of regulations relating to protection against electric shock, including the need for additional protection :

The use of RCD's (Residual Current Devices) with a residual operating current not exceeding 30mA is the
recognised means of providing this additional protection in the event of failure of the provision for basic protection
and or the provision for fault protection or carelessness by users :

Such RCD's should not be used to provide the sole means of protection and do not obviate the need to apply one or
more of the recognised protective measure as detailed in the regulations :

Under the new regulations an installation is required to incorporate one or more RCD's, depending upon the
circumstances. Such instances include:-
• All socket outlets not exceeding 20A, but with certain exceptions. One such exception would be permitted for
a specific labelled or otherwise suitably identified socket outlet for connection of a particular piece of equipment.

• Mobile equipment with a current rating not exceeding 32A for use outdoors

• Electrical circuits installed under “Special installations and locations” as defined in Part 7 of the regulations
e.g. Swimming Pools / Saunas.

• All electrical circuits, including shower and lighting circuits etc. in rooms with a fixed bath or shower e.g.
bathrooms and en-suite bedrooms :

In addition to the protection requirements of the outgoing circuits / loads, the requirements of the installed cabling
also must be taken into account :

Where a cable is concealed in a wall or partition at a depth of less than 50mm from the surface, even if installed in the
“safe zone”, if not provided with earthed mechanical protection e.g. Metal trunking or conduit, it must be
provided with additional protection by means of a 30mA RCD :

Whilst it may be desirable to have one or two circuits fed via an unprotected circuit e.g. an identified / dedicated
freezer circuit, the installation of the wiring may still dictate that the circuit must be RCD protected :

The protection of a circuit by means of a 30mA RCD is also required where cables are concealed in walls constructed
with metal stud partitions which are common in modern buildings, irrespective of the depth from the surface,
unless provided with protection in the form of earthed metallic covering, trunking, conduit or other mechanical
protection so as to avoid damage to the cable during installation or construction of the wall :

In Summary :
Regulations : 411.3.3
Relating to : All socket outlets up to 20A rating for general use by ordinary persons :
Example : - Upstairs sockets - Downstairs sockets - Kitchen sockets - Cooker outlet with integral 13A socket outlet
- Plus any other sockets rated up to 20A including garage sockets
Additional Protection : 30mA RCD ,
Regulations : 701.411.3.3
Relating to : All electrical circuits in a room with a fixed bath or shower
Example : - Shower circuit - Lighting circuit - Heating circuit - Ventilation circuit - Shaver socket - Socket outlets ,
Additional Protection : 30mA RCD ,
Regulations : 522.6.6 / 522.6.7 / 522.6.8 /
All electrical circuits buried in a wall or partition at less than 50mm and without mechanical protection
Example : All concealed wiring - Socket outlets - Lighting circuits - Smoke alarm - Burglar alarm
Additional Protection : 30mA RCD ,

Part P Building Regulations : ( 2392-10 Domestic : ) for Customer ,
Please remember when attempting any electrical installations at home that you are obliged to get the completed job tested by a fully qualified electrician and obtain a minor works certificate. Failure to do this may render your house insurance invalid and you may have difficulty selling your home.

 

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Terms & Conditions : ( this may help self-employed Electricians ) Change some Wording :

:- All material is fully owned by ourselves until invoice is paid off in full, even after installed.

:- Estimates are not fixed quotes and can vary, estimates are approximate minimum-maximum but never a final price.

:- If we do work (including fault finding or cable location etc) then there is a charge and this is not included in free advice.

:- Free advice is general electrical safety recommendations individually to your needs helping to improve the safety of your property/premises.

:- Inspection and testing is included in every invoice as standard (unless specified before work starts) as this is to ensure every circuit worked on complies with current regulations and is safe and fit for use. Sometimes followed with free advice to improve your electrical safety.

:- Inspection and testing is normally including (unless otherwise stated) in all jobs and fully certification given. Certificates are only issued when payment if received in full and all funds have cleared.

:- Duplicate certificates are charged at minimum £ - - per A4 sheet.

:- First invoice is issued and if payment is not received within 10 days (including weekends and bank holidays) a 5% fee is added as late payment and the invoice is resent on day 11 for the extra added amount. Strict 10 days to receive FULL payment, excluding down payments/deposits.

:- Failure to settle account within one calendar month of invoice date will automatically start legal claims proceedings at the FULL rate of invoice. Any discounts / special offers / promotions will be forfeited and reinstated back onto the invoice. All legal costs, late payments fees, additional labour fees can be added to the invoice as decision of Power Plus Electrical. There may be a daily interest applied to any long term outstanding debts until payment cleared in full. Only one reminder is posted as a overdue reminder, this has the 5% added and further to receive payment debt recovery costs started without further warnings.

:- Any equipment requiring hired, i.e. access equipment, other tradesmen (subcontractors, i.e. plumber/builder/carpet fitter/ decorator etc) or any other large cost out with my control will be paid for in advance by yourself the customer (or bill payer) in full before the 1st day of work direct or via ourselves to the subcontractor(s).


:- 1 full years (12 month) guarantee on all parts, labour and any material is included. This does not include access equipment or other trades in guarantee. Lamps, transformers, wear and tear and customer damage/misuse are not included under this clause and chargeable. Any guarantee jobs are only done by ourselves and other contractors services are not refunded.

:- As time, date(s) slot is only agreed when a deposit is paid. A contact is only formed after deposit is received and that time date is arranged, no deposit means no guaranteed start date for work to commence. If work is cancelled without 5 days working notice the deposit is non refundable. More than 5 days prior notice and deposit is fully refundable as long as no material has been ordered. Small jobs normally have no deposit required and can be cancelled at no cost to either party, unless again material is ordered or work has already started. Return materials can have a wholesaler restocking charge.

:- Emergency call out void from a no call out fee, details of call out charge and hourly rate will be explained over the phone. This will vary from job to job , and invoice settled in cash when leaving the property regardless if repaired or return visit required. Return visit is invoiced separately and normally day rates/ costs.

:- Normal working hours at single time are 8am-4:30pm or 9am-5:30pm,, Monday - Friday, including bank holidays, excluding Christmas / New Year. Out with these hours is charged at a higher labour charge.

:- Emergency call out available thought year, 24hour, 365 days a year. (see above).

:- ------- ------- Electrical.co.uk can change its terms and conditions at any time, only in writing if a current contract is already started. No future notice needed to be given to change terms and conditions.

:- Please note that telephone calls are recorded

Fire alarms

Installing a fire alarm is a legal requirement in most commercial and industrial premises Thus alerting of a fire or a smoldering Problem and getting persons and alarm raised quickly. Fire alarms are extremely reliable and with regular testing can be a life- Saving.
Landlords and mains power smoke alarms with battery backup.

Under the common law, Landlords have the duty to ensure the safety of rented property and its contents to Tenants, occupants, neighbors’ or the public do not suffer injury or damage.

The 1991 Smoke Detectors Act, requires that all new houses that have been built since 1992 must, by law, have a smoke detector installed. The minimum requirement being one smoke alarm on each level of the building.

This is not a piece of legislation aimed specifically at residential letting property, but aimed at all new buildings. If an agent installs smoke alarms into properties that he manages or they already exist, care must be taken in ensuring that it is clear

from the letting agreement who is responsible for the maintenance of the detectors including testing and battery replacement.
To neglect this matter could mean that the landlord or agent is responsible, and in the case of a fire could be held liable for being negligent in their duties. There are different rules covering Houses in Multiple Occupation with regard to the installation of smoke detectors and other fire prevention measures.
Installed smoke alarms must be accompanied with a certificate and be tested regularly by pressing the test button. Most landlord insurance requires this certificate and wont payout in the event of a claim. Only qualified electrical contractors can issue this certificate in accordance to BS5839-6.