Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, about an existing electrical installation, any need for an upgrade, and 25A MCBs, is answered by SELECT:
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| A 32A MCB. |
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Question: During a recent fixed wiring installation test at our site, the results highlighted a circuit for a tool wired in 4mm2 singles Ref Method B and protected by a 32A MCB.
The report states that the maximum allowed on this circuit is 28A. This is not in dispute according to BS 7671:2008 but my queries are:
1) Does an existing installation (circa 1985) have to be upgraded to current regulations as a result of this report, or is it acceptable to use this circuit under the auspices of the regulations pertaining at the time of installation?
2) The ideal solution to this situation would be to fit a 25A MCB, but this rating does not seem to be available in the now obsolete range. Am I correct in thinking that 25A rated MCBs are a direct result of the introduction of BS 7671:2008, as I cannot recall ever having fitted an MCB of this rating?
Answer: Firstly, existing installations installed to an earlier edition of the regulations may not comply with the current edition, but this does not necessarily mean they need to be upgraded - see introduction to BS 7671:2008.
Secondly, BS 3871 MCBs of 25A rating were not referred to in the 15th Edition, but were referred to in tables in the 16th Edition prior to 2001 (from which point BS 3871 MCBs were no longer tabulated). This does not necessarily mean that they were not available at the time your installation was made.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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