Re-take - Useful Information for 2394 :

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BS-EN-60898-1 Circuit breakers have replaced the fuses of yesteryear . so the RCDs have been written in stone .

Each manufacturer is free to specify at what range of current the circuit-breaker will react to a perceived ( short circuit )

Circuit breaker is the basic means by which wiring is protected from both a short circuit & overload damage .

Definitions : P/35 . Short-circuit current . An overcurrent resulting from a fault of negligible impedance between ( Live-conductors ) having a difference in potential under normal operating conditions

A fault such as a short-circuit or earth fault , is not an ” Overload ”

Circuit breaker has two independent trip mechanisms: Thermal & Magnetic.
The former reacts to overloads & causes the circuit breaker to trip, while the latter responds to short circuit fault currents.

- Circuit breaker is affected by the temperature of its surroundings
- The magnetic portion of a circuit breaker is sometimes called the instantaneous trip portion.

The defection of the bi-metallic strip depends on the temperature thus the circuit-breaker has a trip temperature and it is the heat generated within the circuit-breaker that causes the temperature to rise, the faster the heat rise, the faster the breaker reaches temperature and trips. Heat is directly proportional to the power (watts)

Under fault conditions .

Magnetic trip level vs. Thermal trip time .
Magnetic trip level / Amperes .
Thermal characteristics (trip time) .. Seconds . ( depending on current level )
Thermal Example : The light draws more than 15A , 10A circuit-breaker for an extended period of time creating a thermal overload.

- Circuit-breaker is not intended to prevent electrical-shock .. That is why you use ( ADS ) RCD / RCBOs ( Additional protection )
- Circuit-breaker does not prevent arcing
- Thermal portions of breakers are affected by ambient temperatures
- Definition P/23 . Ambient Temperature : The temperature of the air or other medium where the equipment is to be used .
( Expected air temperature surrounding the rated circuit breaker )

GN-3 . P/56
Two short-circuit capacity ratings are defined in BS-EN-60898-1 & BS-EN-61009-1 :
( Icn ) the rated short-circuit capacity ( marked on the device )
( Ics ) the service short-circuit capacity .

This has came up on in Exams , before
( Icn ) value ( in Amperes )
( Icn ) is the maximum fault current the device can interrupt safety , although it may no longer be usable
( Icn ) value is marked on the device in a rectangle e.g. ( 6000 ) & for the majority of applications the prospective fault current at the terminals of the circuit-breaker should not exceed this value .

( Ics ) is the maximum fault current the device can interrupt safety , without loss of performance
for domestic installations the ( PFC ) is unlikely to exceed 6kA ... Exams . up to which value ( Icn ) ◄► will equal ( Ics )

O.S.G. Table 7.2.7. P/71
The difference between the two is the condition of the circuit-breaker after manufactures testing . ( Icn ) & ( Ics )

Manufacturer ( Overload )
A slow & small overcurrent situation that causes the ampacity and temperature of the circuit to gradually increase over time.
This type of event is characterized by a slight increase in the load (ampacity) on the circuit and is interrupted by the thermal trip unit of the breaker

Manufacturer ( Breaker definition )
A breaker is a device designed to isolate a circuit during an overcurrent event without the use of a fusible element. A breaker is a resettable protective device that protects against two types of overcurrent situations; Overload & Short Circuit.

Manufacturer ( Short circuit )
A rapid and intense overcurrent situation that causes the ampacity of the circuit to increase. This type of event is characterized by a dramatic increase in
the load (ampacity) on the circuit and is interrupted by the magnetic trip unit of the breaker

Manufacturer ( Overload protection )
The thermal trip unit protects against a continuous overload. The thermal unit is comprised of a bimetal element located behind the circuit breaker trip bar and is part of the breaker’s current carrying path When there is an overload, the increased current flow heats the bimetal causing it to bend. As the bimetal bends it pulls the trip bar which opens the breaker’s contacts.

 

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( Manufacturer )
BS-EN-60898-1 . define the rated current ( In ) of a circuit breaker for low voltage distribution applications as the maximum current that the breaker is designed to carry continuously (at an ambient air temperature of 30°C )

 

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Circuit-breaker is labelled with the rated current in amperes, but without the unit symbol "A" . Instead, the ampere figure is preceded by a letter " B. C . D ", which indicates the instantaneous tripping current

 

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On rant mode .

( MEIWC ) ... classed as , " Certificate "

The Regulations' must state the facts ... ( MEIWC ) You have to prove yourself in any Exams .

P/389 . ( iv ) Competent person will , as appropriate to their function under (i) have a sound knowledge & experience relevant to the nature of the work undertaken & the technical standards set down in these Regulations : be fully versed in the inspection & testing of an installation .

Certification & Reporting
P/398 . (ii) The Minor Work Certificate , required by Part 6 should be made out & signed or otherwise authenticated by a competent person in respect of design , construction , inspection & testing of the ( minor work )

In a case of an alteration or additions of an ( Existing electrical installation )
Minor Electrical installation Work Certificates .. ( MEIWC )

Sometime it helps to break thing down into Q/As .

P/394 . ( MEIWC ) The Minor Work Certificate is intended to be used for :
( Existing electrical circuit ) Additions ) to an installation that ( do not extend ) .. to the provision of a new-circuit .
( Existing electrical circuit ) Alteration ) to an installation that ( do not extend ) .. to the provision of a new-circuit .

Ask yourself what can it be used for . ??
This Certificate may also be used for the replacement of equipment such as accessories or luminaries
This Certificate may also be used for the replacement of socket-outlets .
This Certificate may also be used for the replacement luminaires . etc

( MEIWC ) ... But Not for the replacement of distribution boards or similar items

C&Gs like to hear this one , Appropriate inspection & testing , however , should always be carried out irrespective of the extent of the work undertaken

Point's to be aware of . ( MEIWC )
P/394 . 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 . ( EIC )

 

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Make your Mind up . Certification & Reporting

( EIC )
The Electrical Installation certificate says the work YOU did complies with wiring regulation's . making me a .. ( Safety Certificate 99.9% )

( ECIR )
The main purpose of the Electrcal Installation condition report is to detect so far as is reasonably practicable, and to report , What
likely to impair the safety of an electrical installation ?? ( You can open Pandora's box here )

in theory > Which is not the same as saying the work you have carried out complies with IET Wiring Regulations . ( Reporting )

 

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Inspection

Regulation's has stated the Facts .
Electrical installation's should always be carried out in a safe manner.

Regulation 611.1 of BS-7671: requires that , Inspection precedes testing and is normally to be done with that part of the installation under inspection disconnected from the supply.

 

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Select Committee finding needs industry sense check
19/03/2014

That is the view of NICEIC & ELECSA in response to parliamentary recommendations for all domestic electricians to have a qualification equivalent to NVQ level 3 within the next five years

 

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Responsibility for earthing ... ( under ESQCR )
Where it is necessary for an installation to be earthed to meet the requirements for safety, it is the consumer"s responsibility to ensure the installation is correctly earthed. This is because, in order to receive a supply, the consumer is required to have an installation that meets the safety requirements of regulations 26(1) and 26(2) of The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR).

The safety requirements of regulations 26(1) and 26(2) are that the consumer’s installation is so constructed, installed, protected and used or arranged for use so as to prevent, so far as is reasonably practicable, danger or interference with the distributor’s network or with supplies to others. A consumer"s installation that complies with BS 7671 is deemed to meet these requirements.

In practice the electrical contractor, on behalf of the consumer, should ensure that the installation is correctly earthed before issuing an Electrical Installation Certificate .. ( EIC )

 

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Useful Junk . be fed from a 110V centre tapped transformer .

Extracts .
H&S accepts that a voltage of ( 63.5V to earth ) Three-phase .
( 55V to earth ) single phase , will give protection against severe electrical shock , They therefore recommend that ( Portable tools ) used on construction site(s) . etc

P/61 . Table 41.6 . ( Single-phase ) Uo of 55V , & 63.5V Three-phase

Maximum earth-fault-loop-impedance ( Zs ) Etc . can you get this on any Exams . ??

41.6 :- 32A circuit-breaker ( B ) 32 x 5 = 160A ... Rating / Current .. ( 55V ) ÷ 160A = 0.34Ω , ( 63.5V ) ÷ 160A = 0.396875Ω . 0.40

:- 40A circuit-breaker ( C ) 40 x 5 = 400A ... Rating / Current .. ( 55V ) ÷ 400A = 0.1375Ω , 0.14Ω , ( 63.5V ) ÷ 400A = 0.15875Ω . 0.16


Explanatory note under the table referring to Appendix 14. Note that this appendix is " Informative ", therefore guidance rather than a regulation.

Reduced Low Voltage Systems .

Earth fault loop impedance values for this system may be taken from Table 41.6 of the regulations

 

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P/17 . Regulation 131.5:
‘Conductors other than live conductors, and any other parts intended to carry a fault current, shall be capable of carrying that current without attaining an excessive temperature. Electrical equipment, including conductors, shall be provided with mechanicalprotection against electromechanical stresses of fault currents as necessary to prevent injury or damage to persons, livestock or property.
Note : For live conductors, compliance with Regulation 131.4 assures their protection against overcurrents caused by faults.’
P/17 . Regulation 131.4:
‘ Persons and livestock shall be protected against injury, and property shall be protected against damage, due to excessive temperatures or electromechanical stresses caused by any overcurrents likely to arise in live conductors.’
Types of fault current
There are two types of fault current: short-circuit current and earth fault current, as referred to in the following definitions from Part 2 of BS 7671:
P/34 . ‘ Short-circuit current. An overcurrent resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions.’

P26 . ‘ Earth fault current. A current resulting from a fault of negligible impedance between a line conductor and an exposed-conductive-part or a protective conductor.’

 

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Useful junk .

A cooker control unit is an assembly primarily intended for controlling the supply of electricity to a cooker. It also incorporates a switched socket-outlet for the electrical supply to other electrical appliances. The product standard for cooker control units is BS-4177:1992 - ( P/278 ) Specification for cooker control units. .. Table 53.4.

Table 53.4 of BS-7671:
permits the main switch of a cooker control unit to act as a means of isolation. As for any device used to provide isolation, a cooker control unit should be clearly identified by position or durably marked to indicate the circuit it isolates (Regulation 537.2.2.6 refers). The cooker control unit should be labelled with the word ‘ COOKER ’ adjacent to the main switch that controls the supply to the cooker. Similarly, markings are required such that the ‘ ON ’ and/or ‘ OFF ’ positions of the main switch can be identified.

 

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Q/As . C&Gs . Which of the following features should test probe to GS-38 have .

- Have finger guards ... barriers/guards
- Be rated at 200V a.c.
- Have exposed tips of 4mm or more
- Be coloured identically

The Electricity at Work Regulations 1989 require those in control of part or all of an electrical system to ensure that it is safe to use and that it is maintained in a safe condition.

The most important features that are relevant for electrical test equipment for use by electrically competent people are as follows

(a) Equipment should be, so far as reasonably practicable:
(i) constructed
(ii) maintained
(iii) used in a way to prevent danger .. being responsibly for your own Actions . competent person

It summarises the main issues to be borne in mind when carrying out electrical testing.

(b) No live working unless:
(i) it is unreasonable to work dead
(ii) it is reasonable to work live
(iii) suitable precautions are taken to prevent injury .. being responsibly for your own Actions . competent person

The probes
Electrical test equipment for use by electricians

(i) have finger barriers or are shaped to ( guard ) against inadvertent hand contact with the live conductors under test;
(ii) are insulated to leave an exposed metal tip not exceeding ( 4mm ) measured across any surface of the tip.
Where practicable it is strongly recommended that this is reduced to ( 2mm ) or less, or that spring loaded retractable screened probes are used;

( 4mm ) Dead testing . making contact with accessories .
( 2mm ) Live testing . " Hand's "
Probes can be provided with a variety of shapes of tip to allow access to the different types of contact.

should have suitable high breaking capacity (hbc), sometimes known as hrc, fuse, or fuses, with a low current rating (usually not exceeding 500mA), or a current-limiting resistor and a fuse.

(ii) are coloured so that one lead can be easily distinguished from the other

(vi) do not have accessible exposed conductors other than the probe tips, or have live conductors accessible to a person’s finger if a lead becomes detached from a probe, indicator or instrument when in use. The test lead or leads are held captive and sealed into the body of the voltage detector

The use of test equipment by electricians falls into three main categories
(a) testing for voltage (voltage detection)
forms an essential part of the procedure for proving a system dead before starting work but may also be associated with simple tests to prove the presence of voltage. Items

(b) measuring voltages
(c) measuring current, resistance and (occasionally) inductance and capacitance.

( b & c ) are more concerned with commissioning procedures and fault finding.

(b) No live working unless:

(i) it is unreasonable to work dead
(ii) it is reasonable to work live .. ( fault finding )
(iii) suitable precautions are taken to prevent injury

 

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Who come first ?? Plumber / Gas fitter or Electrician .

Electricity was manly used on street lighting for a replacement for ( Gas ) only later did it gain widespread use in households . Etc

the next Q , So who is ( JPEL/64 )

& how is Harmonisation achieved . ?
The UK Nation Committee responsible for BS-7671: is JPEL/64

J ) joint IET/BSI Committee
P ) Power
EL ) Electrical
64 ) IEC designation for committees dealing with low-voltage electrical installation(s)

Regulation's P/2 . ( JPEL/64 )

 

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Q/As , State the three areas : of reasonability to be recorded on the Electrical Installation Certificate . ( EIC )
The person reasonable for the Design .
The person reasonable for the Construction .
The person reasonable for the Verification . .. Inspection & Testing .

Initial verification . 2.1.
GN-3 . P/15 .
Appx 6 . it is important to recognise the responsibilities of the signatories for the Design . Construction & Verification .

While the inspector is responsible for verifying aspects of both design & construction , he/she cannot & is not meant to absolve responsibility for these elements ; indeed

This is why the inspector carries out the inspection & testing .... so far is reasonably practicable .

recap : GN-3 . P/16 ... Certificate(s) 2.2.
Appendix 6 of BS-7671: contains three model forms for the ( initial certification ) of a new installation
an addition or alteration to an Existing installation

• Multiple signature ( EIC )
• Single signature ( EIC )
• Minor ( MEIWC)

Multiple signature ( EIC )
allows different persons to sign for design , construction , inspection & testing . refer

Single signature ( EIC )
Where design , construction , inspection & testing are the responsibility of one person, a certificate with a single signature may replace the .. multiple signature

Minor ( MEIWC)
This certificate is to be used only for , ( minor work ) that do not include the provision of a new circuit . refer

 

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Q/As 2394 , State what must be recorded on the Electrical Installation Certificate regarding the original electrical installation . ??

the contractor or other person reasonable for the new work . or a person authorised to act on their behalf , shall record on the Electrical Installation Certificate , or the Minor Electrical Installation Work Certificate , any defects found , so far is reasonably practicable in the existing installation BS-7671: 633.2.