Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, about a ring circuit CPC using conduit, is answered by SELECT:
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| Can conduit be used as the CPC? |
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Question: We are currently involved in replacing consumer units within domestic properties during which time we carry out a full inspection & test on the electrical installation. Should we find anything unsatisfactory, or which does not comply with BS7671, we report this back to our client.
A common thing we are finding is conduit being used as a circuit protective conductor (CPC), which I understand is not a problem as long as we check the continuity of this and also the greater cross sectional (CSA - ie adiabatic equation).
Should we be highlighting a problem if the conduit was used as the CPC for a ring circuit, as there is no separate CPC, even though all other tests are satisfactory?
Answer: You should be highlighting a problem if there is a danger, or likely to be a danger. If the conduit is confirmed as suitable, is not exhibiting signs of corrosion etc and an earth 'flying tail' connection is made between the back box and the socket outlet - and ultimately the earth fault loop impedance is satisfactory with regard achieving the necessary disconnection time for the circuit - then it may be safe. In that case, it would not need to be mentioned.
If an installation was installed to an earlier version of the IEE Wiring Regulations and appears to be safe, then there is no need to upgrade it.
The situation with regard a ring final circuit is likely to comply as the conduit will probably have a far greater CSA than two 1.5mm2 conductors - Regulation 543.2.9 mentions that, except where a CPC is formed by a metal enclosure, all conductors in a ring final circuit shall be run in the form of a ring - so conduit as the CPC in this situation is not really a problem.
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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