Re-take - Useful Information for 2394 :

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Extract's from 2009 / 2391 .
Working my way around the Guidance Note 3 . learning curve

Q) Three items to be checked , as identified on the Schedule of Inspections , where fault-protection is provided by automatic disconnection of supply ( ADS )

GN-3 P/20 . Method 1 : automatic disconnection of the supply ( ADS )

You're Q , Presence of appropriate protective-conductor(s)

542.3. Earthing conductor .
Sect 543. Circuit-protective-conductor(s)
Sect 544. Protective bonding conductors
- main bonding conductors
- supplementary bonding conductors .. ( where required )

312.2. The earthing system must be determined e.g.
► TN-C-S system ( protective multiple earthing ( PME))
► TN-S system
► TT system ( earth electrode(s)

411.4.5. The earth fault loop impedance must be appropriate for the protective device i.e. RCD or overcurrent device .

GN-3 P/97 . Schedule of Inspection ( for new installation work only )
Fault protection
i) Automatic disconnection of supply

You're Q . Check for Presence of :
(✓) Presence of earthing conductor
(✓) Presence of circuit-protective-conductors
(✓) Presence of protective-bonding-conductors

Choice of protective devices . ? Circuit-breaker , RCD / RCBO .

Additional protection:
(✓) Presence of resi/dual current devices(s)

O.S.G. P/85/86 Inspection :
9.2.2. Inspection checklist , viii ( d 415.1. additional protection by RCDs )

 

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BS-7671:2011: Learning curve .

[h=4]• On the new Electrical Installation Condition Report, the first few lines of the inspection schedule (1.1 – 1.6 & 3.1) relate to the verification of the distributor’s/supply intake equipment. What should I recommend if that equipment is in a dangerous or potentially dangerous condition[/h]
Where inadequacies in distributor's equipment are observed , the contractor should recommend that the person ordering the report requests the distributor or meter operator , as appropriate , to carry out remedial work as necessary to remove the danger or potential danger .

Distributors and meter operators have an obligation under the Electrical Safety , Quality and Continuity Regulations 2002 ( ESQCR ) to maintain their equipment , so far as is reasonably practicable , to prevent danger .

Condition Report - Inspection schedule P/400
1.1. ) Service cable condition
1.6. ) Condition of isolator ( where present )
3.1. ) Presence and condition of distributor's earthing arrangement ( 542.1.2.1. : 542.1.2.2. )

R/P 403 . Examples of Items requiring Inspection for an Electrical Installation Condition Report
Electrical Intake Equipment
• Service cable
• Service cut-out / fuse
• Meter tails - Distributor
• Meter tails - Consumer
• Meter equipment
• Isolator
Where inadequacies in distributor's equipment are encountered , it is recommended that the person ordering the report informs the appropriate authority

 

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2394 : Calculations

Determine, showing all calculations, whether a test result of 0.06Ω is acceptable if the ► main protective bonding conductor is ( 33m long )
Length of conductor ( 33m )
O.S.G. p182 : Resistance of cable 1.83mΩ/m .. ( Protective-conductor 10mm[SUP]2[/SUP] )
D.C. résistance = ( 33m x 1.83mΩ/m ) /1000

33 x 1.83 = 60.39 ÷ 1000 = 0.06039 .. Q) is this acceptable -&-s

 

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Determine, showing all calculations, whether a test result of 0.06Ω is acceptable if the ► main protective bonding conductor is ( 33m long )
length * milliohms' per metre / 1000

Length of conductor ( 33m )
O.S.G. p182 : Resistance of cable 1.83mΩ/m .. ( Protective-conductor 10mm[SUP]2[/SUP] )
résistance = ( 33m x 1.83mΩ/m ) /1000

33 x 1.83 = 60.39 ÷ 1000 = 0.06039 .. Q) is this acceptable -&-s

Typo error ( D.C. )

 

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From my old notes 16th Edition , Sound advice , My old tutor

Requirement of BS-7671: & the Electrically at Work Act Regulation 1989 That any electrical installation shall be ( Verified ) as safe to operate before being Energised .

The term " Safe to operate " means the user of the electrical installation will be free from the risk of , fire , shock , burns & injury . Etc
" Safe to operate " also means that the user of the installation should not require technical knowledge in order to stay clear of the casualty department of the nearest hospital

 

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Sometimes the term IP is used as an abbreviation for " Ingress Protection "

IP ratings are defined as IPXX. The initial " X " is a number from 0 to 6 indicating the degree of protection against ingress by solid objects, and the second " X " is a number from 0 to 8 indicating the degree of protection against ingress by water.

Degrees of protection against solid objects :

IP0X Non-protected
IP1X 50mm diameter and greater
IP2X 12.5mm diameter and greater
IP3X 2.5mm diameter and greater
IP4X 1.0mm diameter and greater
IP5X dust-protected
IP6X dust-tight

Degrees of protection against water : ( Liquid protection )
X Indicates no specified protection

IPX0 Non-protected
IPX1 Vertically falling water drops ( such as from condensation from surfaces )
IPX2 Vertically falling water drops with enclosure tilted up to 15 degrees ( vertical )
IPX3 Spraying water ( at any angle up to 60° on either side of the vertical )
IPX4 Splashing water ( against the enclose from any direction )
IPX5 Water jets ( projected against the enclosure from any direction , such as from hosepipes )
IPX6 Powerful water jets ( projected against the enclosure from any direction , such as from power jets sprays , or sea waves )
IPX7 Temporary immersion ( of enclosure in water under specified conditions )
IPX8 Continuous immersion ( of enclosure under specified conditions )

Equipment enclosures of an installation need to be correctly selected, installed and maintained to meet the requirements of BS-7671, and the manufacturer. For example, an enclosure needs to have an appropriate IP code, and impact résistance against any likely mechanical damage. Cable glands fitted to an enclosure also need to have an IP code at least equal to that of the enclosure.

Covers of an enclosure need to be securely fixed, and access doors left tightly shut.


The most commonly quoted IP codes in the 17th edition are IPXXB or IP2X, and IPXXD or IP4X. The X denotes that protection is not specified, not that there is no protection. For example,

IPXXB denotes protection against finger contact only
IPXXD denotes protection against penetration by 1mm diameter wires only

 

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IP Codes
This guide gives basic information about the IP (International Protection)1 code, based on information given in ‘BS EN 60529: 1992 – Specification for degrees of protection provided by enclosures (IP code)’, where you can find further details if necessary.

BS-EN-60529 describes a system for classifying the degree of protection given by enclosures of electrical equipment. This is to protect:

a) persons against ‘access to hazardous parts inside an enclosure’, and
b) equipment inside an enclosure against the ‘ingress of solid foreign objects or dust’ and ‘the harmful effects from ingress of water or moisture’.

Electrical equipment enclosures are specified in the form IPXX. As appropriate, the ‘first’ and/or ‘second’ X is replaced by a number as shown in Tables 1 and 2, respectively, of this guide.

As an example, for IP2X, the 2 (from Table 1) defines an enclosure giving protection against ingress of solid foreign objects with a diameter of 12.5 mm, and from a finger being inserted and accessing hazardous parts; the X means there is no protection against ingress of water specified.


A letter A, B, C or D, as shown in Table 3, is sometimes added after XX. As an example, IPXXB, the XX means that the first and second numbers are not specified, and the B means finger protection is provided against any hazard in the enclosure.
Table 1
Protection of equipment inside the enclosure against ingress of solid objects or dust
1st number :
0 . No protection
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . No protection
1 . 50mm diameter object 50
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . Back of hand
2 . 12.5mm diameter solid foreign object 12.5
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . Finger standard jointed test ( 12mm diameter , 80mm length )
3 . 2.5mm diameter solid object 2.5mm
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . Tool
4 . 1.0mm diameter solid foreign object 1mm
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . Wire
5 . Dust-protected ( Ingress of dust not totally prevented , but must not interfere with satisfactory operation of equipment or reduce safety )
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure . Wire
6 . Dust-tight ( No ingress of dust
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure .

Additional Letter of IP Code table 3
Protection of persons against access to hazardous ( live or moving ) parts inside the enclosure
Letter ( A ) Back of hand ( 50mm diameter )
Letter ( B ) Standard jointed test finger ( 12mm diameter 80mm length )
Letter ( C ) Tool 2.5mm diameter 100mm length
Letter ( D ) Wire 1.0mm diameter 100mm length

 

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IP2X . finger protection , This is barriers and enclosures generally
IPXXB . This means the same as above , Only the ( B ) stands for finger barrier
IP4X . This is a standard for the top of enclosures such as consumer units

 

[Richard Burns]

612.4.5. Basic protection by a barrier or an enclosure provided during erection .
Where basic protection is intended to be afforded by a barrier or an enclosure provided during erection in accordance with Regulation 416.2. it shall be verified by a test that each barrier or enclosure affords a degree of protection not less than IPXXB or IP2X , or IPXXD or IP4X as appropriate , where that regulation so requires .

Basic protection by a barriers or enclosures provided during erection

This is a test to verify that each barrier or enclosure provided during erection gives suitable protection against the risk of electric shock through contact with live parts by fingers , solid objects and the like .

The test also applies to barriers or enclosures which , although provided in factory-built equipment , have been affected by the erection process . for example , if an opening has been formed in an enclosure on site for the entry of cables , but is oversized or unused , the enclosure must be capable of meeting the test criteria in order to comply with the requirements of BS-7671:2008:2011: if the enclosure fails to comply when tested , remedial action should be taken (such as reducing the size of the opening )

The degree of protection provided by each barrier or enclosure must not be less than ( IP2X ) or ( IPXXB )
For readily accessible top surfaces the degree of protection must not be less than ( IP4X).

IP2X means that the barrier or enclosure provides protection against contact with live parts by a standard test finger which is ( 12mm in diameter , 80mm long and is capable of bending through 90° twice in the same plane ) like a normal finger . The test finger is applied with a force , not exceeding a specified maximum value and is used in conjunction with an electric signalling circuit . ( IPXXB ) is equivalent to ( IP2X ) in this context .

IP4X is protection against the entry of a wire , strip or similar object which is more than ( 1mm thick ) or a foreign object which is greater than 1mm diameter )

in practice a ( Visual Inspection ) will usually be sufficient to confirm the compliance or otherwise of the barriers or enclosures with the above requirements . if all unused entries are suitably closed , a test may not be necessary .

BS-7671:2008:2011: P/67 barriers or enclosures .. Top of Consumer unit or DB
416.2.2. A horizontal top surface of a barriers or enclosure which is readily accessible shall provide a degree of protection of at least IPXXD or IP4X

BS-7671:2008:2011: P/67 barriers or enclosure .. Side & Bottom
(iii) where an intermediate barrier providing a degree of protection of at least ( IPXXB or IP2X ) prevents contact with live parts , by the use of a key or tool to remove the intermediate barrier

 

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The Chief Examiners’ Report has been reintroduced as a result of feedback from centres, to give them guidance in preparing candidates for the written examination.

2394 : Please read GN-3 that's why it's called Guidance Notes

There appears to be a lot of misunderstanding regarding the testing of an earth-electrode for a generator. In this particular case the generator was the standby supply for a rural ambulance station.

Common errors included:
Seeking permission to isolate the supply to the installation to carry out the test: result in the generator starting up. The supply did not require isolation but the generator did. Stating the test is carried out with an earth-fault-loop-impedance-tester or a low-résistance-ohmmeter when the test is performed using an earth electrode résistance tester.

Incorrect location of the test electrodes: these were often placed either side of the electrode under test. When correctly located the distance between the electrode under test and the current electrode dictates the positioning of the potential electrode being centred and at + 10% and - 10% of the stated overall distance.

Many candidates used varying overall distances (acceptable) but then stated a potential electrode moved 3 m, some at 6 m etc, which was not 10% of their given overall distance.

Electrodes correctly located and then tests carried out between each electrode in turn.

 

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Ring final circuit is protected by a ( BS-3036 ) semi-enclosed-rewirable-fuse . Table 41.2.
& the measured ( Zs ) is 0.97Ω

This is a ring final circuit the disconnection time has to be 0.4s . from Table 41.2 - BS-7671: the maximum ( Zs ) for a 30A rewirable-fuse ( 1.09Ω )

The rule of thumb can now be applied which means that 80% of the value must be calculated.
This can be achieved by multiplying it be 0.80 ... 1.09 x 0.80 = 0.87Ω

The measured value for the circuit must now be lower than the corrected value if it is to comply with BS-7671:

Measured value - 0.97Ω
Corrected value - 0.87Ω

The measured value of ( Zs ) is higher
When recording ( Zs ) for a circuit , measuring ( Ze ) and then adding ( R1 + R2 ) is the preferred method because it will give an accurate value

Whereas direct measurement will include parallel paths and because of this will often give lower readings
Ze + ( R1 + R2 ) should always be used for an initial verification as the ( first recorded value ) will be used as a benchmark to be compared with results taken in ( future periodic tests )

 

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The résistance of the copper conductors will rise by 2% for each 5°C rise in temperature , with that in mind if the ( R1 + R2 ) values are measured at 20°C , and the temperature of the conductor rises to its maximum temperature of 70°C when carrying a load , you can see that the temperature rise of the conductors is 50°C .

As the résistance rises by 2% for each 5°C rise in temperature then the résistance must rise by 20% , as there is 10 x 5°C in 50°C . if the rise is 2% for each 5°C then the increase in résistance will be 10 x 2% = 20%

To increase any value by 20% you simply multiply it be ( 1.2 ) O.S.G. Table 13 ...... ( 1.2 ) is the multiplier for temperature correction .

Table 12 O.S.G.
Ambient temperature multipliers to Table 11
Expected ambient temperature ( °C )
5°C .. Multiplier values 0.94 ............ The résistance of the copper conductors will rise by 2% for each 5°C rise in temperature .
10°C .. Multiplier values 0.96 ............ etc
15°C .. Multiplier values 0.98 ............ etc
20°C .. Multiplier values 1.00 ............ etc
25°C .. Multiplier values 1.02 ............ etc

Table 13 O.S.G. Multiplier to be applied to Table 11 to calculate conductor résistance at maximum operating temperature ( note 3 ) for standard devices ( note 4 )

different scenarios .

Where the ( R1 + R2 ) values for the circuit length have been calculated using the r1 + r2 values from Table 11 O.S.G.
Q) Circuit is wired in 2.5mm with a 1.5mm CPC and is 21m long .
Value of r1 + r2 for this size copper conductor is 19.51mΩ/m at 20°C
21m of this cable will have a résistance ( R1 + R2 ) of ........ 19.51 x 21 ÷ 1000 = 0.4Ω

This is of course at 20°C . you now have to calculate the résistance at which the conductor will be if it is operating at a temperature of 70°C
To do this you must multiply the R1 + R2 value by a factor of ( 1.2 ) ........... 0.4 x 1.2 = 0.48Ω

This will be the résistance which the conductor will reach at 70°C . To calculate ( Zs ) you must add ( 0.48 ) to the measured ( Ze value ) This value of ( Zs ) can now be directly compared with the maximum values given for ( Zs ) in chapter 41 of BS-7671: Providing your value is equal to or less than the maximum value the circuit will be satisfactory .

Chapter 41 : Protection against electric shock .

Where the length of the circuit is not known and the value of R[SUP]1[/SUP] + R[SUP]2[/SUP] has been measured using the ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) method an accurate calculation can be obtained by using the multiplier values provided in

Table 12 O.S.G.
Ambient temperature multipliers to Table 11
Expected ambient temperature ( °C )
5°C .. Multiplier values 0.94
10°C .. Multiplier values 0.96
15°C .. Multiplier values 0.98
20°C .. Multiplier values 1.00
25°C .. Multiplier values 1.02

This is because the table is intended to be used to calculate the résistance value of a conductor when you known the temperature that is going to operate at . in you case you are going to measure the temperature of the room , & calculate the résistance of the cable back to what it would be at 20°C

Ambient temperature multipliers to be applied to ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) values are shown in Table 12 O.S.G.

Example : that you have measured an ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) value of ( 0.84Ω ) and you have measured the ambient temperature at 25°C
by calculation : R[SUP]1[/SUP] + R[SUP]2 [/SUP]/ temp/factor - the value of résistance at 20°C ..... 0.84 ÷ 1.02 = 0.82Ω value of résistance at 20°C

Having corrected the measured value to what it would be at 20°C ., the next step is to calculate what the résistance of the cable would be at its operating temperature

This is where you use the ( 1.2 multiplier ) .. Table 13 O.S.G.
The résistance of the cable at its maximum operating temperate of 70°C .... 0.82 x 1.2 = 0.98Ω
This value can now be added to the measured ( Ze ) to provide a value of ( Zs ) which can be compared to the maximum ( Zs values ) provided in Chapter 41 of BS-7671:

 

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The ( Ze ) of an installation is 0.32Ω
A circuit has been installed using T&E 70°C thermoplastic ( pvc ) cable
The room is 25°C and the measured ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) value is 0.52Ω

The circuit is protected by , BS-EN-60898-1 20A type C circuit-breaker
Correct the cables résistance to 20°C by using the factor from O.S.G. Table 12 P/183

By calculations' : 0.52 ÷ 1.02 = 0.51Ω
Adjust this value to the conductor operating temperature by increasing it by 20% .. By calculations' : 0.51 x 1.2 = 0.61Ω
You must add this value to the installation ( Ze ) to find ( Zs ) .. By calculations' : 0.61 + 0.32 = 0.93Ω

This is the calculated value of ( Zs ) when the circuit is operating at its maximum capacity
This value can now be compared directly to the maximum value of ( Zs ) for a 20A BS-EN-60898-1 type C circuit-breaker .
Your value is Table R/P 56 , 41.3 , C circuit-breaker 20A - 1.15Ω
To comply with the regulation , the actual value of 0.93Ω must be equal to / or lower than the maximum value which is 1.15Ω

 

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This is probably the most used and is certainly the most convenient as it requires one measurement and one minimal calculation , this method is known as the rule of thumb .

R/P 56 Table 41.3.
The circuit is protected by a 32A type B - BS-EN-60898-1 circuit-breaker with a maximum ( Zs ) value of 1.44Ω The ( Zs ) for the circuit has been obtained by ( Direct measurement ) and is 1.18Ω , All that is required for this method is to look up the maximum ( Zs ) permissible for the protective device .

You must multiply the maximum value by ( 0.8 ) 1.44 x 0.8 = 1.15Ω
You must now compare the measured value to the recalculated maximum value ,
The measured value must be EQUAL to or LOWER than the recalculated maximum value

You can see the measured values is 1.18Ω and the recalculated value is 1.15Ω .

2394 , You call < > your measured value is HIGHER of the TWO . is it Acceptable or Not .

 

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GN-3 This Guidance Note is concerned principally with Part 6 of BS-7671: Inspection & Testing

• Gaining familiarity with IET Guidance Note 3 and its content is also an important aspect .
• The BS-7671: requirements for initial verification , inspection , testing & certification & reporting .
Interpretation of test results is a vital part of the testing process , Why ? The correct selection and use of tables from BS-7671: and from O.S.G. & GN-3

Inspection & Testing of electrical installation(s)
Why inspect & test

The Electricity at Work Regulation 1989 is a ( statutory document ) it is a legal requirement that statutory regulations are complied with .
These regulations are required to ensure that places of work provide a safe , well maintained system .
To provide this is to ensure the newly installed circuit(s) and existing installations are , Tested on a regular basis

By the book GN-3 : 3.3. Electricity at Work Regulations
Regulation 4(2) of the Electricity at Work Regulations 1989 requires that :
As may be necessary to prevent danger , all systems shall be maintained so as to prevent , so far is reasonably practicable , such danger , refer .

The British standard for electrical installations is BS-7671:2008:2011: the requirement for electrical installations , Within this standard , Regulation
Electrical : test certificates are used to record what has been done and confirm that the installation meets the required standard Regulation 610.1. States that " every installation shall , during erection and on completion before being put into service , be inspected and tested to verify , so far as reasonably practicable . that the requirements of the regulations have been met "

Certification & Reporting

Electrical Installation Certificate .. ( EIC )
Minor Electrical Installation Works Certificate .. ( MEIWC )

BS-7671:2011: has stated the facts .
This Report is an important and valuable document ....
Electrical Installation Condition Report .. ( EICR ) - Condition Report - for the person producing the Reporting
This Report should only be used for reporting on the condition of an existing electrical installation
Periodic Inspection & Testing .. The purpose of this Condition Report is to Confirm , so far as reasonably practicable , whether or not the electrical installation is in a satisfactory condition for continued service

GN-3 1.3. The client
1.3.1. Certificates and Reporting .
Following the periodic inspection and testing of an existing installation , an ( EICR ) together with schedule of inspection and schedule of test results , are required to be given to person ordering the inspection

( EICR ) documentation comprises the following .. Purpose of
Schedule of Inspections .. one or more
Condition Report Inspection Schedule for Domestic & Similar with up to 100A supply ..... Note : This form is suitable for many types of smaller installations not exclusively domestic .
( Generic ) Schedule of Test Results .. one or more ... Test results and compared with relevant criteria

GN-3 Periodic inspection
3.9.1. Example - checklist of items that require inspection
The following is a copy of the checklist in Appendix 6 of BS-7671:2008(2011) which lists items at ( various locations within an installation that may require inspection )