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amberleaf
Recommendation Codes applied to Observations - 2008. Learning Curve .
• Exposed live parts that are accessible to ( Touch ) such as where live conductors have no ( or damaged ) insulation
• Incorrect polarity , or protective device in neutral conductor only .
• A 30/32A ring-final-circuit discontinuous or cross-connected with another circuit .
• Unable to trace final circuit(s)
• Insulation résistance of less than 1MΩ between live conductors connected together & Earth , when measured at the ( CCU ) with all final-circuits connected
• Exposed live parts that are accessible to ( Touch ) such as where live conductors have no ( or damaged ) insulation
• Incorrect polarity , or protective device in neutral conductor only .
• A 30/32A ring-final-circuit discontinuous or cross-connected with another circuit .
• Unable to trace final circuit(s)
• Insulation résistance of less than 1MΩ between live conductors connected together & Earth , when measured at the ( CCU ) with all final-circuits connected
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amberleaf
What’s in a Regulation
Regulation 132.10.
I do feel some improvement can be made on some Regulations . as so far as in the (( Wording ))
132.10. Disconnecting devices
It must be possible to isolate-circuits or equipment for:
- Inspection
- Testing
- Fault detection
- Maintenance & repair
Any devices must comply with Chapter 53 of BS-7671:
132.10. Disconnecting devices
To be provided for:
- Inspection
- Testing
- Fault detection
- Maintenance & repair
132.10 Disconnecting devices
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
Circuit(s) or Individual items of equipment as required for operation (( so what does the regulations say ))
For what reasons
- Inspection ..
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Testing
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Fault detection
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Maintenance & repair
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
132.10. Disconnecting devices for isolation and/ or switching
Disconnecting devices for switching and/or isolation shall be provided in a readily accessible place so that
The Electrical installation
All Individual circuits and
All Items of equipment
are as far as possible unable to present danger as required for:
- Operation
- Inspection
- Testing
- Fault detection
- Maintenance and repair
Regulation 132.10.
I do feel some improvement can be made on some Regulations . as so far as in the (( Wording ))
132.10. Disconnecting devices
It must be possible to isolate-circuits or equipment for:
- Inspection
- Testing
- Fault detection
- Maintenance & repair
Any devices must comply with Chapter 53 of BS-7671:
132.10. Disconnecting devices
To be provided for:
- Inspection
- Testing
- Fault detection
- Maintenance & repair
132.10 Disconnecting devices
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
Circuit(s) or Individual items of equipment as required for operation (( so what does the regulations say ))
For what reasons
- Inspection ..
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Testing
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Fault detection
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
- Maintenance & repair
Disconnecting (( devices )) shall be provided so as to (( permit switching )) and/or (( Isolation of the electrical installation ))
132.10. Disconnecting devices for isolation and/ or switching
Disconnecting devices for switching and/or isolation shall be provided in a readily accessible place so that
The Electrical installation
All Individual circuits and
All Items of equipment
are as far as possible unable to present danger as required for:
- Operation
- Inspection
- Testing
- Fault detection
- Maintenance and repair
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amberleaf
132.15. Isolation and switching
Part 4 of the IET Regulations deals with the application of protective-measures for safety and Chapter 53 with the regulations for switching devices or switchgear required for protection, isolation and switching of a consumer’s installation.
( CCU ) The consumer’s main switchgear must be readily accessible to the consumer and be able to :
- Isolate the complete installation from the supply
- Protect against overcurrent
- Cut of the current in the event of a serious fault occurring
132.15.1. Effective means ,
Suitably placed for ready operation . shall be provided so that all (( voltages may be cut off )) from every installation .
- from every-circuit therefore and / or from all-equipment .
- as may be necessary to prevent or remove danger
132.10 should not mention isolation, only disconnection or switching.
132.15.1 and .2 are meant to be covering isolation, so the removal of all voltage i.e. there is sufficient gap to prevent danger.
132.15.2 is a repeat of 132.15.1 but instead of everything they only mention fixed motors
The wording is all mixed up. in some Regulations
Part 4 of the IET Regulations deals with the application of protective-measures for safety and Chapter 53 with the regulations for switching devices or switchgear required for protection, isolation and switching of a consumer’s installation.
( CCU ) The consumer’s main switchgear must be readily accessible to the consumer and be able to :
- Isolate the complete installation from the supply
- Protect against overcurrent
- Cut of the current in the event of a serious fault occurring
132.15.1. Effective means ,
Suitably placed for ready operation . shall be provided so that all (( voltages may be cut off )) from every installation .
- from every-circuit therefore and / or from all-equipment .
- as may be necessary to prevent or remove danger
132.10 should not mention isolation, only disconnection or switching.
132.15.1 and .2 are meant to be covering isolation, so the removal of all voltage i.e. there is sufficient gap to prevent danger.
132.15.2 is a repeat of 132.15.1 but instead of everything they only mention fixed motors
The wording is all mixed up. in some Regulations
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amberleaf
Wiring regulation 134.1.1 states that manufactures-instructions must be followed when installing electrical equipment......
Quote : Cooker .. ( Isolation )
Electrical connections
The cooker must be supplied via a suitable (( double pole isolating switch )) having a contact separation of at least 3mm in all poles placed in a readily accessible position adjacent to the cooker.
Functional switching .. An operation intended to switch “ On or Off
Functional switching ( Control )
Quote : Cooker .. ( Isolation )
Electrical connections
The cooker must be supplied via a suitable (( double pole isolating switch )) having a contact separation of at least 3mm in all poles placed in a readily accessible position adjacent to the cooker.
Functional switching .. An operation intended to switch “ On or Off
Functional switching ( Control )
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amberleaf
The following is an analysis of possible changes for Amendment No 2, after it had been reviewed by CAG 25 Nov 2011.
Each panel is asked to “consider/reconsider” each of the comments below ASAP. The panel should: Agree, indicate if Editorial or T), Not agree, amend (propose something similar or new), WIP or allocate to AMD 3
132.15.1 and 132.15.2
Comment (justification for change)
132.15.1 and 132.15.2 should be deleted as the fundamental requirement for disconnecting devices is now to be found in the new regulation 132.10. Furthermore, there is no need for the content of regulation 132.15.2 (which relates to only one type of equipment) to actually appear in Chapter 13 (fundamental principles )
Specific requirements for motor control arrangements already exist elsewhere in BS 7671 and the general requirements for isolation, switching for mechanical maintenance, functional switching and emergency switching contained in section 537 should be applied to motors as appropriate to particular circumstances.
We now have two regulations (132.10 and 132.15.1) saying much the same thing with differing degrees of emphasis.
Proposed change
132.15.1 and 132.15.2 should be deleted
Note: A previous response to this deletion made during the final phase of Amd No 1, was:
132.15.2 which, as previously stated, has no logical place in Part 1 of the regulations and which is very commonly misunderstood by users of BS 7671.
These regulations should not be deleted, for the following two reasons.
(1) Approved Document P clause 0.1 indicates that the requirements of Schedule 1 to regulation 7 of the Building Regulations for England and Wales will be met by adherence to the fundamental principles in Chapter 13 of BS 7671. Those fundamental principles will be deficient without Regulations 132.15.1 and 132.15.2.
(2) Regulation 12 of the Electricity at Work Regulations 1989 requires means for isolation.
But it was also agreed that “ the issue be reconsidered for Amd 2 ”
Each panel is asked to “consider/reconsider” each of the comments below ASAP. The panel should: Agree, indicate if Editorial or T), Not agree, amend (propose something similar or new), WIP or allocate to AMD 3
132.15.1 and 132.15.2
Comment (justification for change)
132.15.1 and 132.15.2 should be deleted as the fundamental requirement for disconnecting devices is now to be found in the new regulation 132.10. Furthermore, there is no need for the content of regulation 132.15.2 (which relates to only one type of equipment) to actually appear in Chapter 13 (fundamental principles )
Specific requirements for motor control arrangements already exist elsewhere in BS 7671 and the general requirements for isolation, switching for mechanical maintenance, functional switching and emergency switching contained in section 537 should be applied to motors as appropriate to particular circumstances.
We now have two regulations (132.10 and 132.15.1) saying much the same thing with differing degrees of emphasis.
Proposed change
132.15.1 and 132.15.2 should be deleted
Note: A previous response to this deletion made during the final phase of Amd No 1, was:
132.15.2 which, as previously stated, has no logical place in Part 1 of the regulations and which is very commonly misunderstood by users of BS 7671.
These regulations should not be deleted, for the following two reasons.
(1) Approved Document P clause 0.1 indicates that the requirements of Schedule 1 to regulation 7 of the Building Regulations for England and Wales will be met by adherence to the fundamental principles in Chapter 13 of BS 7671. Those fundamental principles will be deficient without Regulations 132.15.1 and 132.15.2.
(2) Regulation 12 of the Electricity at Work Regulations 1989 requires means for isolation.
But it was also agreed that “ the issue be reconsidered for Amd 2 ”
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amberleaf
Consumer Units for Domestic Household and other Premises .
17[SUP]th[/SUP] Edition wiring regulations incorporating Amendment No 3 :2015
Firstly ; Regulations relating to 421.1.201. (( Enhancement of Fire Safety )) caused by Electrical Equipment
421.1.201 that is intended to improve fire safety in domestic premises.
421.1.201. as far as is reasonably practicable, to contain any fire within the enclose and to minimise flames from escaping caused mainly as a result of poorly installed connections .
The crucial importance of checking that all electrical connections are properly made
(( Screw terminals to make significantly reducing risk of loose connections )) manufacturer’s PS wish list
The intent of Regulation 421.1.201. is that it applies to consumer units and similar switchgear assemblies to BS-EN-61439-3 inside all domestic ( household ) premises including their integral / attached garages and outbuildings or those in close proximity .
One of the most common fault . :yesnod: Neutral conductor
Failure to tighten neutral conductor connections to the same torque as line conductor connections due to a misconception that neutral conductors carry less current.
Inadvertently taking cable insulation inside the terminal at a connection, resulting in the securing screw or the clamp of the terminal not making proper contact with the conductor.
Failure to check factory installed connections for tightness where required to do so by the manufacturer; and tightening connections to an incorrect torque and/or with inappropriate tools.
Good workmanship and proper materials must be used, and account must be taken of the manufacturer’s relevant instructions, if any.
17[SUP]th[/SUP] Edition wiring regulations incorporating Amendment No 3 :2015
Firstly ; Regulations relating to 421.1.201. (( Enhancement of Fire Safety )) caused by Electrical Equipment
421.1.201 that is intended to improve fire safety in domestic premises.
421.1.201. as far as is reasonably practicable, to contain any fire within the enclose and to minimise flames from escaping caused mainly as a result of poorly installed connections .
The crucial importance of checking that all electrical connections are properly made
(( Screw terminals to make significantly reducing risk of loose connections )) manufacturer’s PS wish list
The intent of Regulation 421.1.201. is that it applies to consumer units and similar switchgear assemblies to BS-EN-61439-3 inside all domestic ( household ) premises including their integral / attached garages and outbuildings or those in close proximity .
One of the most common fault . :yesnod: Neutral conductor
Failure to tighten neutral conductor connections to the same torque as line conductor connections due to a misconception that neutral conductors carry less current.
Inadvertently taking cable insulation inside the terminal at a connection, resulting in the securing screw or the clamp of the terminal not making proper contact with the conductor.
Failure to check factory installed connections for tightness where required to do so by the manufacturer; and tightening connections to an incorrect torque and/or with inappropriate tools.
Good workmanship and proper materials must be used, and account must be taken of the manufacturer’s relevant instructions, if any.
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amberleaf
Extracts .
Similar switchgear assemblies :icon_bs:
The phrase ‘similar switchgear assemblies’ in Regulation 421.1.201 means those assemblies used for the same fundamental application as a consumer unit. A consumer unit is defined in Part 2 of BS-7671:
‘Consumer unit (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices proven during the type-test of the assembly as suitable for such use.’
An example of a similar switchgear assembly is a three phase distribution board that is intended to be operated by ordinary persons. This would have to have isolation that interrupts the three incoming line conductors and the neutral, rather than just double-pole isolation as mentioned in the above definition. :aureola:
Similar switchgear assemblies :icon_bs:
The phrase ‘similar switchgear assemblies’ in Regulation 421.1.201 means those assemblies used for the same fundamental application as a consumer unit. A consumer unit is defined in Part 2 of BS-7671:
‘Consumer unit (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices proven during the type-test of the assembly as suitable for such use.’
An example of a similar switchgear assembly is a three phase distribution board that is intended to be operated by ordinary persons. This would have to have isolation that interrupts the three incoming line conductors and the neutral, rather than just double-pole isolation as mentioned in the above definition. :aureola:
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amberleaf
Regulation 421.1.201 was principally introduced to cover the interior of a household building and any garage or other outbuildings integral, attached, or in close proximity to that building.
The intent of Regulation 421.1.201. is that it applies to consumer units and similar switchgear assemblies to BS-EN-61439-3 inside all domestic ( household ) premises including their integral / attached garages and outbuildings or those in close proximity .
The intent of Regulation 421.1.201. is that it applies to consumer units and similar switchgear assemblies to BS-EN-61439-3 inside all domestic ( household ) premises including their integral / attached garages and outbuildings or those in close proximity .
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amberleaf
( BR ) What’s the right height for fixing socket outlets, switches and controls ?
It all depends on what sort of building you are working on and if it is:
New
Complete rewire would be an opportunity to install accessories in line with Building Regulations
Existing
In existing dwellings, switches and controls are generally higher and outlets lower than the mounting heights required by Building Regulations.
re-cap (A2)
Sockets that are too LOW should be moved - 553.1.6 page 174
A socket-outlet on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket-outlet or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug
In a world of ever-changing legislation
Regulation 132.12 & Building regulations Part M
Electrical equipment is referenced in two separate parts of the Building Regulations:
Part P of the Building Regulations relates to electrical safety in dwellings.
The approved document prescribes that switches, sockets and consumer units in new dwellings should be easy to reach, in accordance with Part M of the building regulations.
Part M which deals with access to and use of buildings, and recommends that switches sockets and other equipment should be located between 450mm and 1200mm from finished floor level and does not specifically mention the consumer unit.
However, Part P suggests one way to comply is by mounting the consumer unit so that the switches are between 1350mm and 1450mm from the finished floor level.
The consumer unit also needs to be accessible
therefore the location and the height need to be taken into consideration. For instance a small under-stair cupboard may be classed as difficult to access and hence be an unsuitable place to install a consumer unit. Care should also be taken that the consumer unit is placed in a position where it not likely to be damaged by impact.
Stair cupboard may be classed as difficult to (( access ))
I wish the DNO was consulted on this matter over the years, alcoves or cupboard(s) high up near the ceiling.. “ Unique concept ” you wonder why Electricians have back trouble , Risks and assumptions
Compliance BS-7671: (A2)
• Regulation 132.12 Accessibility of electrical equipment bullet point (ii)
Electrical equipment shall be arranged so as to afford as may be necessary:
(ii) accessibility for operation, inspection, testing fault detection, maintenance and repair.
re-cap (A2) Existing
Sockets that are too LOW should be moved - 553.1.6 page 174
A socket-outlet on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket-outlet or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug
It all depends on what sort of building you are working on and if it is:
New
Complete rewire would be an opportunity to install accessories in line with Building Regulations
Existing
In existing dwellings, switches and controls are generally higher and outlets lower than the mounting heights required by Building Regulations.
re-cap (A2)
Sockets that are too LOW should be moved - 553.1.6 page 174
A socket-outlet on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket-outlet or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug
In a world of ever-changing legislation
Regulation 132.12 & Building regulations Part M
Electrical equipment is referenced in two separate parts of the Building Regulations:
Part P of the Building Regulations relates to electrical safety in dwellings.
The approved document prescribes that switches, sockets and consumer units in new dwellings should be easy to reach, in accordance with Part M of the building regulations.
Part M which deals with access to and use of buildings, and recommends that switches sockets and other equipment should be located between 450mm and 1200mm from finished floor level and does not specifically mention the consumer unit.
However, Part P suggests one way to comply is by mounting the consumer unit so that the switches are between 1350mm and 1450mm from the finished floor level.
The consumer unit also needs to be accessible
therefore the location and the height need to be taken into consideration. For instance a small under-stair cupboard may be classed as difficult to access and hence be an unsuitable place to install a consumer unit. Care should also be taken that the consumer unit is placed in a position where it not likely to be damaged by impact.
Stair cupboard may be classed as difficult to (( access ))
I wish the DNO was consulted on this matter over the years, alcoves or cupboard(s) high up near the ceiling.. “ Unique concept ” you wonder why Electricians have back trouble , Risks and assumptions
Compliance BS-7671: (A2)
• Regulation 132.12 Accessibility of electrical equipment bullet point (ii)
Electrical equipment shall be arranged so as to afford as may be necessary:
(ii) accessibility for operation, inspection, testing fault detection, maintenance and repair.
re-cap (A2) Existing
Sockets that are too LOW should be moved - 553.1.6 page 174
A socket-outlet on a wall or similar structure shall be mounted at a height above the floor or any working surface to minimize the risk of mechanical damage to the socket-outlet or to an associated plug and its flexible cable which might be caused during insertion, use or withdrawal of the plug
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amberleaf
In the form of Isolation . Kitchen Safety
(ESC)
2013 : if appliances such as fridges , dishwashers , washing machines are fitted under worktops’ , getting to (( Socket-outlets )) may be difficult . ideally , these appliances should be controlled by a (( Switched fuse connection unit )) mounted above the worktops where you can reach it easily
A washing machine etc. will normally fit into a space and the only way to reach the isolation point (Plug and socket) would be to pull out the machine
Isolation switches for white goods in a kitchen
So the main (( Question )) is the plug is readily available would remove the requirement to fit isolators. ( 99.9% NO )
in an “ Emergency “ aspect
Washing machine was why you wanted to switch if off dragging it out while it is trying to bash you kitchen to pieces is not really an option .
So in your case here , After sore knuckles , The Means of isolation should be provided .
Washing machines
Dishwashers
Tumble dryers
Under counter fridges Etc
Isolation Switch .
Shower isolation switch
Cooker isolation switch
Main isolation switch ( CCU )
Isolation of kitchen appliances .. the need for , to fit isolators ( Spurs )
Isolation for fans in Bathrooms Etc .
(ESC)
2013 : if appliances such as fridges , dishwashers , washing machines are fitted under worktops’ , getting to (( Socket-outlets )) may be difficult . ideally , these appliances should be controlled by a (( Switched fuse connection unit )) mounted above the worktops where you can reach it easily
A washing machine etc. will normally fit into a space and the only way to reach the isolation point (Plug and socket) would be to pull out the machine
Isolation switches for white goods in a kitchen
So the main (( Question )) is the plug is readily available would remove the requirement to fit isolators. ( 99.9% NO )
in an “ Emergency “ aspect
Washing machine was why you wanted to switch if off dragging it out while it is trying to bash you kitchen to pieces is not really an option .
So in your case here , After sore knuckles , The Means of isolation should be provided .
Washing machines
Dishwashers
Tumble dryers
Under counter fridges Etc
Isolation Switch .
Shower isolation switch
Cooker isolation switch
Main isolation switch ( CCU )
Isolation of kitchen appliances .. the need for , to fit isolators ( Spurs )
Isolation for fans in Bathrooms Etc .
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amberleaf
(A2) 2011: CCUs loose connections .
Where torque settings for connection tightness are specified in manufacturers’ instructions, does this mean installers must confirm these settings during work using a torque driver
Regulations 134.1.1 and 510.3 state that manufacturers’ instructions are to be taken into account during installation work. It is necessary to check that all connections are tight, and the use of a torque screwdriver is one way of confirming this.
134.1.1 Erection
510.3 Every item of equipment Etc . refer :icon_bs:
Where torque settings for connection tightness are specified in manufacturers’ instructions, does this mean installers must confirm these settings during work using a torque driver
Regulations 134.1.1 and 510.3 state that manufacturers’ instructions are to be taken into account during installation work. It is necessary to check that all connections are tight, and the use of a torque screwdriver is one way of confirming this.
134.1.1 Erection
510.3 Every item of equipment Etc . refer :icon_bs:
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amberleaf
Known one ask for ( Vd ) anymore
Reminder . 612.14. Verification of voltage drop
Note : Verification of voltage drop is not normally required during initial verification .
it’s just a learning curve
Voltage drop calculations .. Voltage drop = mV x Ib x length / 1000
Where the voltage drop is in volts and:
mV is the millivolts dropped per ampere per metre
Ib is the design current of the current of the circuit ( the current intended to be carried )
Length is the length of the circuit in metres. The division by 1000 gives the answer in volts .
Résistance of copper conductor
in order to design for compliance with BS-7671 limiting values of earth fault loop impedance given in Tables 41.2 to 41.4 it is necessary to establish the relevant impedance of the circuit conductors concerned at their operating temperatures
O.S.G. Table 11 1.5mm[SUP]2[/SUP] with 1.0mm[SUP]2[/SUP] earth , CPC is given as 30.20mΩ therefore if the cable is 20mts in length this will be
30.20 x 20 ÷ 1000 = 0.60Ω which is the value of R[SUP]1[/SUP] + R[SUP]2[/SUP]
( VD ) ( A2 ) 2011 .. “ Single cables “
Identify a suitable cable - Table 4D1A P/332 reference method B
1mm[SUP]2[/SUP] cable has a rating of ( 4 ) 13.5A
Calculate the voltage drop ( Vd ) BS-7671: Table 4D1B P/333 reference method A & B .. Conduit
Voltage drop = ( mV/A/m ) x Ib x L ÷ 1000 .. 44 x 4.35 x 23 ÷ 1000 = 4.4V
Appendix 4 P/314
This circuit complies with the requirements of BS-7671:2011: in the calculated volte drop ( 4.4V ) is less than the maximum permitted ( 3% ) for a single phase lighting circuit .. Single phase 3% of 230V = 6.9V
Reminder . 612.14. Verification of voltage drop
Note : Verification of voltage drop is not normally required during initial verification .
it’s just a learning curve
Voltage drop calculations .. Voltage drop = mV x Ib x length / 1000
Where the voltage drop is in volts and:
mV is the millivolts dropped per ampere per metre
Ib is the design current of the current of the circuit ( the current intended to be carried )
Length is the length of the circuit in metres. The division by 1000 gives the answer in volts .
Résistance of copper conductor
in order to design for compliance with BS-7671 limiting values of earth fault loop impedance given in Tables 41.2 to 41.4 it is necessary to establish the relevant impedance of the circuit conductors concerned at their operating temperatures
O.S.G. Table 11 1.5mm[SUP]2[/SUP] with 1.0mm[SUP]2[/SUP] earth , CPC is given as 30.20mΩ therefore if the cable is 20mts in length this will be
30.20 x 20 ÷ 1000 = 0.60Ω which is the value of R[SUP]1[/SUP] + R[SUP]2[/SUP]
( VD ) ( A2 ) 2011 .. “ Single cables “
Identify a suitable cable - Table 4D1A P/332 reference method B
1mm[SUP]2[/SUP] cable has a rating of ( 4 ) 13.5A
Calculate the voltage drop ( Vd ) BS-7671: Table 4D1B P/333 reference method A & B .. Conduit
Voltage drop = ( mV/A/m ) x Ib x L ÷ 1000 .. 44 x 4.35 x 23 ÷ 1000 = 4.4V
Appendix 4 P/314
This circuit complies with the requirements of BS-7671:2011: in the calculated volte drop ( 4.4V ) is less than the maximum permitted ( 3% ) for a single phase lighting circuit .. Single phase 3% of 230V = 6.9V
A
amberleaf
( A2 ) 2011
it’s just a learning curve ( Q )
BS-7671: identifies that the cross sectional area of a conductor shall be determined by :
a) the admissible maximum temperature
b) the nominal voltage
c) voltage tolerance
d) the earthing system
You go straight to BS-7671:2011 :icon_bs: index and look up ( CSA ) of conductors and cables P/442 , you will find reference to 132.6. Sec 524
you would now look in Part 1 Chapter 32 regulation 6 P/19
Your Answer is : The ( CSA ) of conductor(s) shall be determined for both (( normal operating conditions )) and where appropriate , for fault conditions according to : (i) the admissible maximum temperature
Therefore you know that ( A ) must be the answer .
it’s just a learning curve ( Q )
BS-7671: identifies that the cross sectional area of a conductor shall be determined by :
a) the admissible maximum temperature
b) the nominal voltage
c) voltage tolerance
d) the earthing system
You go straight to BS-7671:2011 :icon_bs: index and look up ( CSA ) of conductors and cables P/442 , you will find reference to 132.6. Sec 524
you would now look in Part 1 Chapter 32 regulation 6 P/19
Your Answer is : The ( CSA ) of conductor(s) shall be determined for both (( normal operating conditions )) and where appropriate , for fault conditions according to : (i) the admissible maximum temperature
Therefore you know that ( A ) must be the answer .
A
amberleaf
( A2 ) 2011 :icon_bs:
it’s just a learning curve ( Q )
The algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation is known as the :
a) residual current .... (( resi/dual-current ))
b) harmonic current
c) Line current
d) Neutral current
P/444 looking in the BS-7671:2011: index the only (( Phrase you can find )) from the Question is Electrical installation , Definition Part 2
looking in Part 2 Definitions P/33 . (( Residual current ))
Algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation
it’s just a learning curve ( Q )
The algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation is known as the :
a) residual current .... (( resi/dual-current ))
b) harmonic current
c) Line current
d) Neutral current
P/444 looking in the BS-7671:2011: index the only (( Phrase you can find )) from the Question is Electrical installation , Definition Part 2
looking in Part 2 Definitions P/33 . (( Residual current ))
Algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation
A
amberleaf
( A2 ) 2011
it’s just a learning curve ( Q ) :icon_bs:
Which one of the following cannot be used as ( Basic Protection )
a) isolation of live parts
b) barriers or enclosures
c) protective earthing and bonding
d) obstacles
Options – a,b,d. all provide basic protection .. refer to Section 416 & 417 . P/66 / P/67
Option (c) provides fault-protection .. what is your Answer
it’s just a learning curve ( Q ) :icon_bs:
Which one of the following cannot be used as ( Basic Protection )
a) isolation of live parts
b) barriers or enclosures
c) protective earthing and bonding
d) obstacles
Options – a,b,d. all provide basic protection .. refer to Section 416 & 417 . P/66 / P/67
Option (c) provides fault-protection .. what is your Answer
A
amberleaf
( Ze ) External loop impedance ... ( Testing you have proven an Earth into the building ) important test
( Zs ) = The earth fault loop impedance of the (( internal current carrying circuit ))
R[SUP]1[/SUP] + R[SUP]2[/SUP] = the sum of the résistance of the Line-conductor ( R[SUP]1[/SUP] ) and the circuit-protective-conductor ( R[SUP]2[/SUP] ) between the point of utilisation and the origin of the installation . Equitation Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
( Zs ) = The earth fault loop impedance of the (( internal current carrying circuit ))
R[SUP]1[/SUP] + R[SUP]2[/SUP] = the sum of the résistance of the Line-conductor ( R[SUP]1[/SUP] ) and the circuit-protective-conductor ( R[SUP]2[/SUP] ) between the point of utilisation and the origin of the installation . Equitation Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
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[h=5]Meter Tail Investigation Report[/h]Download the full report ◄
Meter Tail Investigation Report , 805.00 KB ◄
Meter Tails
Electrical Safety Council ( ESC )
Investigation looking at the effects on the terminals of consumer unit main switches when the (( Meter Tails )) are disturbed using reference standard BS-EN-60947-1:2007 + A1: 2011
( CCU ) To assess the mechanical strength (( tightness )) of meter tail screw terminal connections typically found in consumer unit main switches . following
[url]http://www.electricalsafetyfir...htness-of-meter-tails/[/URL]
Meter Tail Investigation Report , 805.00 KB ◄
Meter Tails
Electrical Safety Council ( ESC )
Investigation looking at the effects on the terminals of consumer unit main switches when the (( Meter Tails )) are disturbed using reference standard BS-EN-60947-1:2007 + A1: 2011
( CCU ) To assess the mechanical strength (( tightness )) of meter tail screw terminal connections typically found in consumer unit main switches . following
[url]http://www.electricalsafetyfir...htness-of-meter-tails/[/URL]
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amberleaf
IET . 2015
Commonly, loose connections within consumer units can lead to overheating – one of the main causes of the units catching fire. With many based under the staircases of residential buildings, such fires can block exit routes and impede the ability to escape.
Commonly, loose connections within consumer units can lead to overheating – one of the main causes of the units catching fire. With many based under the staircases of residential buildings, such fires can block exit routes and impede the ability to escape.
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amberleaf
Extracts BS-7671: 2001 (2004) ◄
Unwanted tripping
Unwanted tripping of RCDs can occur when a protective-conductor-current or leakage-current causes unnecessary operation of the RCD.
An RCD must be so selected and the electrical circuits so subdivided that any protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device (Regulation 531-02-04 refers). Such tripping can occur on heating elements, cooking appliances etc., which may have elements that absorb a small amount of moisture through imperfect elementend seals when cold. When energised, this moisture provides a conductive path for increased leakage and could operate the RCD. The moisture dries out as the element heats up. Although not precluded in BS 7671, it is not a requirement to use an RCD on such circuits if other satisfactory means of protection are available. Providing an RCD with a higher rated residual operating current may solve the problem but the requirements of the Regulations would still have to be met.
Unwanted tripping
Unwanted tripping of RCDs can occur when a protective-conductor-current or leakage-current causes unnecessary operation of the RCD.
An RCD must be so selected and the electrical circuits so subdivided that any protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device (Regulation 531-02-04 refers). Such tripping can occur on heating elements, cooking appliances etc., which may have elements that absorb a small amount of moisture through imperfect elementend seals when cold. When energised, this moisture provides a conductive path for increased leakage and could operate the RCD. The moisture dries out as the element heats up. Although not precluded in BS 7671, it is not a requirement to use an RCD on such circuits if other satisfactory means of protection are available. Providing an RCD with a higher rated residual operating current may solve the problem but the requirements of the Regulations would still have to be met.
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Extracts BS-7671:2008(2013) :icon_bs:
Unwanted operation :svengo:
Unwanted operation of RCDs can occur when a :aureola: protective-conductor-current causes the RCD to operate under non-fault conditions, i.e. the accumulative of protective conductor currents developed by the switch-mode power supplies of computers, e.g. too many computers on one circuit. An RCD must be so selected and the electrical circuits so subdivided that any protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary operation of the device (see Regulation 531.2.4). Such operation can occur on circuits with heating elements of cooking appliances etc., where elements can absorb a small amount of moisture through imperfect seals when cold. When energised, this moisture provides a conductive path for current to flow and could operate the RCD. The moisture dries out as the element heats up. Although not precluded in BS 7671, it is not a requirement to use an RCD on such circuits but the requirements of the Regulations would still have to be met, i.e. cables in walls, Regulation 522.6.101.
Unwanted operation :svengo:
Unwanted operation of RCDs can occur when a :aureola: protective-conductor-current causes the RCD to operate under non-fault conditions, i.e. the accumulative of protective conductor currents developed by the switch-mode power supplies of computers, e.g. too many computers on one circuit. An RCD must be so selected and the electrical circuits so subdivided that any protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary operation of the device (see Regulation 531.2.4). Such operation can occur on circuits with heating elements of cooking appliances etc., where elements can absorb a small amount of moisture through imperfect seals when cold. When energised, this moisture provides a conductive path for current to flow and could operate the RCD. The moisture dries out as the element heats up. Although not precluded in BS 7671, it is not a requirement to use an RCD on such circuits but the requirements of the Regulations would still have to be met, i.e. cables in walls, Regulation 522.6.101.
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amberleaf
Ring-final-circuit .
Learning curve .
This also has the benefit that successful test results in Step 2 & Step 3 will confirm that the socket has been correctly wired and the polarity is correct.
End-to-end
r[SUP]1[/SUP] = 0.6Ω
r[SUP]N [/SUP] = 0.6Ω
r[SUP]2 [/SUP]= 1.0Ω
R[SUP]1[/SUP] and R[SUP]N[/SUP] should be the same as the ( CSA ) areas of neutral & line-conductor(s) should be the same in a single-phase-circuit
( T&E ) 2.5mm[SUP]2[/SUP] & circuit-protective-conductor 1.5mm[SUP]2 [/SUP] ... ( CSA ) of the CPC is indeed smaller than the ( CSA ) Line & neutral
The reading expected in Step 2 .
i) ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) / 4
ii)
iii) ( 0.6 + 0.6 = 1.2 ) ÷ 4
iv) = 0.3Ω
The reading expected in Step 3 .
i) ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) / 4
ii) ( 0.6 + 1.0 = 1.6 ) ÷ 4
iii) = 0.4Ω
The actual readings obtained in Step 2 & 3 have been recorded .
Socket-outlet (1) Step 2 0.31Ω , Step 3 0.41Ω
Socket-outlet (2) Step 2 0.3Ω , Step 3 0.4Ω
Socket-outlet (3) Step 2 0.32Ω , Step 3 0.41Ω
like any test result , very close to the expected values .
Learning curve .
This also has the benefit that successful test results in Step 2 & Step 3 will confirm that the socket has been correctly wired and the polarity is correct.
End-to-end
r[SUP]1[/SUP] = 0.6Ω
r[SUP]N [/SUP] = 0.6Ω
r[SUP]2 [/SUP]= 1.0Ω
R[SUP]1[/SUP] and R[SUP]N[/SUP] should be the same as the ( CSA ) areas of neutral & line-conductor(s) should be the same in a single-phase-circuit
( T&E ) 2.5mm[SUP]2[/SUP] & circuit-protective-conductor 1.5mm[SUP]2 [/SUP] ... ( CSA ) of the CPC is indeed smaller than the ( CSA ) Line & neutral
The reading expected in Step 2 .
i) ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) / 4
ii)
iii) ( 0.6 + 0.6 = 1.2 ) ÷ 4
iv) = 0.3Ω
The reading expected in Step 3 .
i) ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) / 4
ii) ( 0.6 + 1.0 = 1.6 ) ÷ 4
iii) = 0.4Ω
The actual readings obtained in Step 2 & 3 have been recorded .
Socket-outlet (1) Step 2 0.31Ω , Step 3 0.41Ω
Socket-outlet (2) Step 2 0.3Ω , Step 3 0.4Ω
Socket-outlet (3) Step 2 0.32Ω , Step 3 0.41Ω
like any test result , very close to the expected values .
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amberleaf
2394
Q/As
A circuit breaker to BS-3871 is marked “ M6 ″ explain what this marking means and describe how the same information would be marked on a circuit breaker to BS-EN-60898-1.
M6 means the circuit breaker has a breaking capacity of 6kA. On a BS-EN-60898-1 circuit breaker it would be marked as the figure 6000 inside a rectangular box.
Q/As
A circuit breaker to BS-3871 is marked “ M6 ″ explain what this marking means and describe how the same information would be marked on a circuit breaker to BS-EN-60898-1.
M6 means the circuit breaker has a breaking capacity of 6kA. On a BS-EN-60898-1 circuit breaker it would be marked as the figure 6000 inside a rectangular box.
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amberleaf
2394
Q/As
Earth fault loop impedance can be calculated from measured values of Ze, ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
a) state the equation to be used
b) explain why a measured value of earth fault loop impedance may be less than a value calculated as above.
a) Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
b) Ze is measured with the earthing-conductor disconnected from the main earthing terminal. Zs is measured with all bonding connected and this may provide parallel paths which reduce the apparent value of Zs.
Q/As
Earth fault loop impedance can be calculated from measured values of Ze, ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
a) state the equation to be used
b) explain why a measured value of earth fault loop impedance may be less than a value calculated as above.
a) Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
b) Ze is measured with the earthing-conductor disconnected from the main earthing terminal. Zs is measured with all bonding connected and this may provide parallel paths which reduce the apparent value of Zs.
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2394
Q/As
An insulation resistance test is to be carried out on a lighting circuit. State the action to be taken in respect of :
a) lamps
b) light switches
c) two-way light switches
a) remove lamps or switch off locally if removal is not possible
b) put light switches ‘on‘ unless the switch is being used to isolate lamps which cannot be removed
c) operate two-way switches alternately while applying the test voltage to ensure that both strappers and the switch wire are tested
Q/As
An insulation resistance test is to be carried out on a lighting circuit. State the action to be taken in respect of :
a) lamps
b) light switches
c) two-way light switches
a) remove lamps or switch off locally if removal is not possible
b) put light switches ‘on‘ unless the switch is being used to isolate lamps which cannot be removed
c) operate two-way switches alternately while applying the test voltage to ensure that both strappers and the switch wire are tested
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2394
Q/As
An insulation resistance test is to be carried out on a lighting circuit. State the action to be taken in respect of vulnerable equipment including smoke detectors and self-contained emergency lighting luminaries.
Isolate the vulnerable equipment or disconnect it. If this is not possible then only test between all (( live conductors )) connected together and earth.
Q/As
An insulation resistance test is to be carried out on a lighting circuit. State the action to be taken in respect of vulnerable equipment including smoke detectors and self-contained emergency lighting luminaries.
Isolate the vulnerable equipment or disconnect it. If this is not possible then only test between all (( live conductors )) connected together and earth.
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2394 / 2395
Q/As
Explain briefly why it is desirable to minimise the amount of dismantling during a periodic inspection and test.
Dismantling introduces the risk of:
i) damage
ii) incorrect reassembly
iii) forgetting to reassemble
Q/As
Explain briefly why it is desirable to minimise the amount of dismantling during a periodic inspection and test.
Dismantling introduces the risk of:
i) damage
ii) incorrect reassembly
iii) forgetting to reassemble
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amberleaf
Q/As
State the maximum rating of a RCD used for:-
a) protecting a 63A socket outlet on a construction site
b) fire protection in an area with a high risk of fire due to the materials
c) protecting a socket outlet supplying a caravan.
a) 500mA
b) 300mA
c) 30mA
State the maximum rating of a RCD used for:-
a) protecting a 63A socket outlet on a construction site
b) fire protection in an area with a high risk of fire due to the materials
c) protecting a socket outlet supplying a caravan.
a) 500mA
b) 300mA
c) 30mA
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amberleaf
Q/As Yeah they do ask this one .
Describe briefly how to measure the prospective fault current at a three-phase distribution board.
Measure the prospective short-circuit current between each line and neutral. Take the highest reading and double it to get the prospective fault current.
Describe briefly how to measure the prospective fault current at a three-phase distribution board.
Measure the prospective short-circuit current between each line and neutral. Take the highest reading and double it to get the prospective fault current.
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2394
Q/As
1) List two statutory documents applying to the conduct of inspection and testing and one statutory document requiring installations to meet the standards set out in BS 7671.
2) List two main things to be agreed with the client prior to inspecting and testing an existing installation and state where these should be recorded.
3) List five things to check before using a test instrument and its leads.
4) State the instruments which would have the following ranges:-
0-2Ω
0-200 MΩ
0-20 kA
1) Two statutory documents relating to the conduct of inspection and testing:
Health and Safety at Work etc. Act 1974
Electricity at Work Regulations 1989
Electricity Safety, Quality and Continuity Regulations 2002 requires installations to meet requirements of BS 7671.
2) Two things to be agreed with client:
Extent
Limitations
Record these on the Electrical Installation Condition Report form.
3) Five points should be given. See GS-38.
Instrument :
- in good condition
- calibrated
- battery ok
- suitable for voltage it is to be used on
- suitable ranges for the measurement to be taken.
Leads:
in good condition
adequately insulated for the voltage they are to be used on
fused and/or fitted with resistors to limit current
probes fitted with finger guards
probe tips with bare minimum of exposed metal (2mm or less) or
else covered by retractable spring loaded shrouds
adequate length
coloured to aid identification
4) a) low resistance ohmmeter,
b) insulation resistance ohmmeter,
c) prospective fault current meter
Q/As
1) List two statutory documents applying to the conduct of inspection and testing and one statutory document requiring installations to meet the standards set out in BS 7671.
2) List two main things to be agreed with the client prior to inspecting and testing an existing installation and state where these should be recorded.
3) List five things to check before using a test instrument and its leads.
4) State the instruments which would have the following ranges:-
0-2Ω
0-200 MΩ
0-20 kA
1) Two statutory documents relating to the conduct of inspection and testing:
Health and Safety at Work etc. Act 1974
Electricity at Work Regulations 1989
Electricity Safety, Quality and Continuity Regulations 2002 requires installations to meet requirements of BS 7671.
2) Two things to be agreed with client:
Extent
Limitations
Record these on the Electrical Installation Condition Report form.
3) Five points should be given. See GS-38.
Instrument :
- in good condition
- calibrated
- battery ok
- suitable for voltage it is to be used on
- suitable ranges for the measurement to be taken.
Leads:
in good condition
adequately insulated for the voltage they are to be used on
fused and/or fitted with resistors to limit current
probes fitted with finger guards
probe tips with bare minimum of exposed metal (2mm or less) or
else covered by retractable spring loaded shrouds
adequate length
coloured to aid identification
4) a) low resistance ohmmeter,
b) insulation resistance ohmmeter,
c) prospective fault current meter
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amberleaf
List two factors affecting the measured value of earth fault loop impedance of a given circuit.
a) State a simple rule for taking account of the factors in a) above when comparing measured values of
b) Zs with the maximum values given in BS 7671.
a) circuit loading and ambient temperature
b) Measured values of Zs should not exceed 80% of the maximum given in the tables in Chapter 41 of BS 7671. (Appendix 14 of BS-7671)
a) State a simple rule for taking account of the factors in a) above when comparing measured values of
b) Zs with the maximum values given in BS 7671.
a) circuit loading and ambient temperature
b) Measured values of Zs should not exceed 80% of the maximum given in the tables in Chapter 41 of BS 7671. (Appendix 14 of BS-7671)
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a) State the practical advantage that measuring Rl + R2 has over the alternative method of measuring c.p.c. continuity.
b) Say when it is necessary to use the alternative method.
c) State the percentage rise in the resistance of a copper conductor between 20°C and 70°C.
a) Measuring R1 + R2 requires meter leads of standard length whereas the alternative long lead method, measuring R2, requires a lead the length of the circuit.
b) The alternative ‘long lead’ method must be used for checking the continuity of bonding conductors.
c) 20%
b) Say when it is necessary to use the alternative method.
c) State the percentage rise in the resistance of a copper conductor between 20°C and 70°C.
a) Measuring R1 + R2 requires meter leads of standard length whereas the alternative long lead method, measuring R2, requires a lead the length of the circuit.
b) The alternative ‘long lead’ method must be used for checking the continuity of bonding conductors.
c) 20%
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amberleaf
2394
Q/As
Outline the dangers which could arise during the following tests:
a) insulation resistance test
b) earth fault loop impedance test
c) RCD test
a) The use of high voltages creates a risk of shock and the risk of damaging vulnerable equipment.
b) If the c.p.c. is broken then every exposed conductive part downstream from the break will be live during the test and present a shock risk.
c) Danger is the same as for b)
A SELV circuit in zone 0 of a bathroom is being inspected. State:-
a) the BS number of the safety isolating transformer
b) the maximum voltages allowed ( both ac and dc )
c) where the transformer should be located
a) the BS-EN number of the safety isolating transformer
b) 12Vacor30Vdc
c) Outside zones 0, 1 and 2
The continuity of the conductors of a ring final circuit is checked using the method given in IET Guidance Note 3. List four things which are confirmed by satisfactory readings. Assume that testing has been done through the front of the sockets using a test lead with a plug.
1) the ring is continuous
2) the value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
3) there are no interconnections in the ring
4) socket outlets are correctly connected
Q/As
Outline the dangers which could arise during the following tests:
a) insulation resistance test
b) earth fault loop impedance test
c) RCD test
a) The use of high voltages creates a risk of shock and the risk of damaging vulnerable equipment.
b) If the c.p.c. is broken then every exposed conductive part downstream from the break will be live during the test and present a shock risk.
c) Danger is the same as for b)
A SELV circuit in zone 0 of a bathroom is being inspected. State:-
a) the BS number of the safety isolating transformer
b) the maximum voltages allowed ( both ac and dc )
c) where the transformer should be located
a) the BS-EN number of the safety isolating transformer
b) 12Vacor30Vdc
c) Outside zones 0, 1 and 2
The continuity of the conductors of a ring final circuit is checked using the method given in IET Guidance Note 3. List four things which are confirmed by satisfactory readings. Assume that testing has been done through the front of the sockets using a test lead with a plug.
1) the ring is continuous
2) the value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
3) there are no interconnections in the ring
4) socket outlets are correctly connected
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amberleaf
2395 Practical assessment
You will do an insulation résistance test on a single-phase consumer unit , Here you would have to identify 2 faults which would either be a short-circuit , low-résistance , or and earth-fault .
This is very straightforward and should not pose a problem if you know , how to work with insulation résistance tester .
Points to remember . (( Examiner ))
This might differ from examiner to examiner . if they tell you , :yes: do it in the sequence they tell you , you will be better off doing it their way . if you do not then they will fail you , and challenging them on it will probably not get you very far . :35:
You will do an insulation résistance test on a single-phase consumer unit , Here you would have to identify 2 faults which would either be a short-circuit , low-résistance , or and earth-fault .
This is very straightforward and should not pose a problem if you know , how to work with insulation résistance tester .
Points to remember . (( Examiner ))
This might differ from examiner to examiner . if they tell you , :yes: do it in the sequence they tell you , you will be better off doing it their way . if you do not then they will fail you , and challenging them on it will probably not get you very far . :35:
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amberleaf
2395 Practical assessment
There are also 2 faults to identify out of a possible 7 that the assessor can put on the rig. This could be something like a low insulation résistance, to an open ring-final-circuit. There are not difficult faults trying to trick you, but rather faults you should pick up if you do the tests and interpret the test results correctly.
There are also 2 faults to identify out of a possible 7 that the assessor can put on the rig. This could be something like a low insulation résistance, to an open ring-final-circuit. There are not difficult faults trying to trick you, but rather faults you should pick up if you do the tests and interpret the test results correctly.
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amberleaf
You are pressed for time in the practical part and have quite a few things to remember. Sometimes a small thing like forgetting to prove dead in the correct manner could cost you the whole test. If you do not isolate, lock off and prove dead in accordance with GS-38 then you will fail.
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amberleaf
A very large number of candidates were unable to demonstrate an understanding of voltage drop and its determination during a periodic inspection and test. This is a common and recurring situation across the 2395-302 series of examinations.
A large number of candidates appeared to be aware of the determination of voltage drop during the design of an electrical installation and then attempt to apply that to a periodic inspection. The main incorrect responses included:
• Being unable to explain why voltage drop cannot be determined by direct measurements at the origin and furthest point of the circuit.
• Stating voltage drop can only be determined using the design calculation mV/A/m x Ib x L ÷ 1000 even when this information is not available for an existing installation.
• No correction for conductor operating temperature where resistance is measured at 20°C
Where the method of measurement of conductors was correctly identified a number of candidates lost marks by incorrectly stating measuring R[SUP]1[/SUP] + R[SUP]2 [/SUP]and not ( R[SUP]1[/SUP] & R[SUP]N[/SUP] ) as required for voltage drop. ◄◄◄◄ :6:
( Vd ) Volt drop using test readings .
“ learning curve only ”
Always try to answer the questions in full using the correct terminology
Using ( R[SUP]1[/SUP] + R[SUP]2 [/SUP])
Often the R[SUP]2[/SUP] ( CPC ) will be a conductor with a smaller CSA than the live conductor(s), this of course will result in the calculation showing a higher voltage drop than there would be in reality ( because the current flow in R[SUP]1[/SUP] & R[SUP]N[/SUP] ) ... live conductor(s) L / N
Providing the R[SUP]1[/SUP] + R[SUP]2 [/SUP]calculation give a result of less than the permitted value of 3% ( 6.9V ) or 5% ( 11.5V ) depending on the type of circuit, then all is good . Remember this is only a check , But where the R[SUP]2 [/SUP]calculation for a smaller CPC gives a higher than permitted volt drop it will be worth tying again using R[SUP]N [/SUP]instead .
As an example let’s take a circuit is wired using a 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] T&E , it has an R[SUP]1[/SUP] + R[SUP]2 [/SUP]value of ( 0.6Ω ) and the circuit is protected by a 20A circuit-breaker
Using the R[SUP]1[/SUP] + R[SUP]2 [/SUP]value of ( 0.6Ω ) you can now calculate the voltage drop for the circuit . (( 0.6 x 20 x 1.20 = 14.4V )) This is to high, if you use R[SUP]1[/SUP] + R[SUP]N [/SUP]you may end up with an acceptable result
How to calculate R[SUP]N [/SUP]
The problem is you do not have a reading for ( R[SUP]N [/SUP]) but a simple calculation will give you all of the information you need
CSA line x ( R[SUP]1[/SUP] + R[SUP]2 [/SUP]) = R[SUP]2 [/SUP]
CSA line + CSA cpc
To put figures to this :
2.5 = 0.625 x 0.6 = 0.375Ω
2.5 + 1.5mm[SUP]2 [/SUP]
0.375Ω is the résistance of R[SUP]2 [/SUP], therefore if you subtract this value from the R[SUP]1[/SUP] + R[SUP]2 [/SUP] value you will have the value of R[SUP]2 [/SUP]0.6Ω – 0.375Ω = 0.225Ω
The résistance of the 2.5mm[SUP]2[/SUP] line-conductor is 0.225Ω
Therefore the (( 2.5mm[SUP]2[/SUP] Neutral-conductor will be the same )) if you now double this value you will have (( R[SUP]1[/SUP] + R[SUP]N [/SUP] )) 0.225 + 0.225 = 0.45Ω
Now you can carry out the voltage drop calculation using 0.45Ω as the résistance value . 0.45 x 20 1.20 = 10.8V
3% ( 6.9V ) or 5% ( 11.5V )
A large number of candidates appeared to be aware of the determination of voltage drop during the design of an electrical installation and then attempt to apply that to a periodic inspection. The main incorrect responses included:
• Being unable to explain why voltage drop cannot be determined by direct measurements at the origin and furthest point of the circuit.
• Stating voltage drop can only be determined using the design calculation mV/A/m x Ib x L ÷ 1000 even when this information is not available for an existing installation.
• No correction for conductor operating temperature where resistance is measured at 20°C
Where the method of measurement of conductors was correctly identified a number of candidates lost marks by incorrectly stating measuring R[SUP]1[/SUP] + R[SUP]2 [/SUP]and not ( R[SUP]1[/SUP] & R[SUP]N[/SUP] ) as required for voltage drop. ◄◄◄◄ :6:
( Vd ) Volt drop using test readings .
“ learning curve only ”
Always try to answer the questions in full using the correct terminology
Using ( R[SUP]1[/SUP] + R[SUP]2 [/SUP])
Often the R[SUP]2[/SUP] ( CPC ) will be a conductor with a smaller CSA than the live conductor(s), this of course will result in the calculation showing a higher voltage drop than there would be in reality ( because the current flow in R[SUP]1[/SUP] & R[SUP]N[/SUP] ) ... live conductor(s) L / N
Providing the R[SUP]1[/SUP] + R[SUP]2 [/SUP]calculation give a result of less than the permitted value of 3% ( 6.9V ) or 5% ( 11.5V ) depending on the type of circuit, then all is good . Remember this is only a check , But where the R[SUP]2 [/SUP]calculation for a smaller CPC gives a higher than permitted volt drop it will be worth tying again using R[SUP]N [/SUP]instead .
As an example let’s take a circuit is wired using a 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] T&E , it has an R[SUP]1[/SUP] + R[SUP]2 [/SUP]value of ( 0.6Ω ) and the circuit is protected by a 20A circuit-breaker
Using the R[SUP]1[/SUP] + R[SUP]2 [/SUP]value of ( 0.6Ω ) you can now calculate the voltage drop for the circuit . (( 0.6 x 20 x 1.20 = 14.4V )) This is to high, if you use R[SUP]1[/SUP] + R[SUP]N [/SUP]you may end up with an acceptable result
How to calculate R[SUP]N [/SUP]
The problem is you do not have a reading for ( R[SUP]N [/SUP]) but a simple calculation will give you all of the information you need
CSA line x ( R[SUP]1[/SUP] + R[SUP]2 [/SUP]) = R[SUP]2 [/SUP]
CSA line + CSA cpc
To put figures to this :
2.5 = 0.625 x 0.6 = 0.375Ω
2.5 + 1.5mm[SUP]2 [/SUP]
0.375Ω is the résistance of R[SUP]2 [/SUP], therefore if you subtract this value from the R[SUP]1[/SUP] + R[SUP]2 [/SUP] value you will have the value of R[SUP]2 [/SUP]0.6Ω – 0.375Ω = 0.225Ω
The résistance of the 2.5mm[SUP]2[/SUP] line-conductor is 0.225Ω
Therefore the (( 2.5mm[SUP]2[/SUP] Neutral-conductor will be the same )) if you now double this value you will have (( R[SUP]1[/SUP] + R[SUP]N [/SUP] )) 0.225 + 0.225 = 0.45Ω
Now you can carry out the voltage drop calculation using 0.45Ω as the résistance value . 0.45 x 20 1.20 = 10.8V
3% ( 6.9V ) or 5% ( 11.5V )
A
amberleaf
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amberleaf
Voltage drop in conductors
To check the suitability of the current carrying capacity it is simply a matter of looking at the installation method , and then checking on the current carrying capacity tables for the cable in Appendix 4 of BS-7671
To ensure that the cable meets the voltage drop requirements is slightly more complex , A simple method is to measure the voltage at the origin of the circuit , and then measure the voltage at the end of the circuit with the load connected and switched on , The difference between the two measurements will be the voltage drop .
if the first method is impractical, then a résistance test should be carried out between the Line and Neutral of the circuit. This test is carried out using the same method as the R[SUP]1[/SUP] + R[SUP]2 [/SUP]test although of the test being between Line and CPC (( it is between the Line and Neutral for the circuit ))
Once the résistance of the R[SUP]1[/SUP] + R[SUP]N [/SUP]circuit has been measured it should be multiplied by the current that will flow in the circuit , This will give you the voltage drop for the circuit .
Example . A circuit is wired in 2.5mm[SUP]2[/SUP] & is 25 metres in length . The current in the circuit is 18 amps
Measured value of résistance is 0.37Ω
Voltage drop = I x R = V .. 18 x 0.37 = 6.66 V
To check the suitability of the current carrying capacity it is simply a matter of looking at the installation method , and then checking on the current carrying capacity tables for the cable in Appendix 4 of BS-7671
To ensure that the cable meets the voltage drop requirements is slightly more complex , A simple method is to measure the voltage at the origin of the circuit , and then measure the voltage at the end of the circuit with the load connected and switched on , The difference between the two measurements will be the voltage drop .
if the first method is impractical, then a résistance test should be carried out between the Line and Neutral of the circuit. This test is carried out using the same method as the R[SUP]1[/SUP] + R[SUP]2 [/SUP]test although of the test being between Line and CPC (( it is between the Line and Neutral for the circuit ))
Once the résistance of the R[SUP]1[/SUP] + R[SUP]N [/SUP]circuit has been measured it should be multiplied by the current that will flow in the circuit , This will give you the voltage drop for the circuit .
Example . A circuit is wired in 2.5mm[SUP]2[/SUP] & is 25 metres in length . The current in the circuit is 18 amps
Measured value of résistance is 0.37Ω
Voltage drop = I x R = V .. 18 x 0.37 = 6.66 V
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