Frequently asked questions – the answers are provide by the Institution of Engineering and Technology (IET):
1. Rule of thumb - The factor used in the ‘rule of thumb’ method of assessing measured values of earth fault loop impedance has been quoted as 0 8, 0.78, 75% and 2/3. Which value will be quoted in the 17th Edition?
Answer - It is expected that BS 7671:2008 will state the value of 0.8 in Appendix 14.
2. Availability of BS 7671:2008 - When will BS 7671:2008, the 17th Edition of the IEE Wiring Regulations actually go on sale?
Answer - It is anticipated that BS 7671:2008 will go on sale, from all usual outlets, on Wednesday 2nd January 2008.
3. BS 7671:2008 date of effect - When should installations comply with BS 7671:2008?
Answer - BS 7671:2008 will be available from 2nd January 2008. There will be a period of six-months where the current BS 7671:2001(2004) is phased out and BS 7671:2008 is implemented. Within the six-month period, installations may comply with either version. After the six-month period, i.e. 2nd July 2008, installations should comply only with BS 7671:2008.
4. Long-term installations - Having started work on a long-term project, the completion date is early 2009. This means that the installation was designed and work began on site when the 16th Edition was current but will end when the 17th Edition will be current. How can I ensure the work complies with the relevant standard?
Answer - The client must be consulted and made aware of the situation. An agreement should be reached between the electrical contractor, responsible for the construction element of the electrical work and the client.
5. Alterations and additions to an installation Regulation 131.8, which was previously numbered 130-07-01 in BS 7671:2001(2004), now has been amended to include the words ‘if necessary’. Why?
Answer - When making an alteration or addition to an existing installation, Regulation 131.8 states that, amongst other requirements, the earthing and bonding arrangements are to be adequate for the intended altered circumstance. The words ‘if necessary’ have been added to clarify that, in some instances, the condition of the existing earthing and bonding arrangements may not have any bearing on the intended altered circumstance and would, therefore, not need to be upgraded.
6. Protective bonding - It has been established whilst assessing an existing installation, prior to an alteration to the fixed installation, that the main equipotential conductors are undersized and do not comply with the 17th Edition. Is this acceptable?
Answer - There has been no change or relaxation from the 16th Edition. Regulation 131.8 requires that the bonding arrangements are adequate and the requirements for sizing such conductors can be found in Chapter 54.
7. 17th Edition is not to be applied retrospectively - Whilst undertaking a Periodic Inspection, it is apparent that the installation complies with the 16th Edition of the IEE Wiring Regulations but not the 17th Edition. How do I record the information on the Periodic Inspection Report?
Answer - Periodic Inspection Reports are intended to convey a description of the current state and are to inform of any matters which may affect the safe operation of an installation. An installation may not have been designed and installed to the 17th Edition but may still be fit for purpose and safe for continued use.
8. Appendices of BS 7671:2008 - There are now fifteen appendixes in the 17th Edition, compared with seven in the current version. What is the status of the appendices and are they regulatory?
Answer - Each appendix is shown to be normative or informative; this information is shown on the title page of each appendix. Normative means that the information contained is regulatory and holds the same status as the main body of the Regulations, whilst informative means that the information contained is included for guidance purposes only. An informative appendix is part of the Standard but not part of the Regulations.
9. Reproduction of today's lecture notes - I am a lecturer. May I reproduce the contents of the lecture notes for my students?
Answer - The lecture notes are the copyright of the Institution of Engineering Technology and may not be reproduced without permission.
10. Deletion of Regulation 413-02-12 and Table 41C - Table 41C of BS 7671:2001(2004), which currently gives maximum permitted impedances of circuit protective conductors and is used as an alternative method of providing earth fault protection, does not appear in the 17th Edition. Why not?
Answer - The requirements of Regulation 413-02-12 and Table 41C have been deleted from the 17th Edition. Where the value of earth fault loop impedance exceeds the maximum value given in tables 41.2, 41.3 or 41.4 and, hence, disconnection will not occur in the required time, Regulation 411.3.2.6 of the 17th Edition states that supplementary bonding shall be provided in accordance with Regulation 415.2. Alternatively, Regulation 411.4.9 states that an RCD may be used to satisfy the disconnection requirements of Regulation 411.3.2.2.
11. Disconnection times of RCDs - What are the required disconnection times for S-type, time-delayed, RCDs?
Answer - BS 61008-1 states that the device must open in 0.5s when tested at Io n, however, to meet the requirements of BS 7671:2008, disconnection times should comply with Table 41.1 of Regulation 411.3.2.2.
12. Testing of RCDs - Generally, installations complying with the 17th Edition will require more RCDs than installations currently complying with the 16th Edition. More RCDs require more testing which will mean more disruption in domestic and commercial environments. What are the testing requirements of RCDs?
Answer - The requirements remain un changed from the 16th Edition. Regulation 514.12.2 requires that a notice be fixed near to the origin of the installation informing that the RCD be tested by pressing the test button quarterly; Part 6 has requirements for initial verification and Periodic Inspection reporting which remain unchanged.