Nick asks this question, which concerns a metal consumer unit as part of a solar PV installation, and electromagnetic effects. It has been answered by the NICEIC (Theme – Regulations and Legislation):
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Question: After an inspection of this metal consumer unit (see photo), one of many faults found with this recent solar PV installation was that the line and neutral are not through the same hole – however Regulation 521.5.1 reads:
‘The conductors of an AC circuit installed in a ferromagnetic enclosure shall be arranged so that all line conductors and the neutral conductor, and the appropriate protective conductor are within the same enclosure. Where such conductors enter a ferrous enclosure, they shall be arranged such that the conductors are only collectively surrounded by ferromagnetic material.’
In general, this seems to be ignored (i.e. the protective conductor). However, I have done a little research and some information states that whilst minor, an earth fault current could exist for a short period of time. Would this mean in the case of this example, and excluding an SWA with separate circuit protective conductor (CPC), they should enter via the same hole?
I do concede the effects would be minimal.
Answer: The conductors of an AC circuit entering a metal enclosure must not be separated by ferromagnetic material unless precautions are taken to minimise the effects of eddy currents. Eddy currents can result in heating and, in extreme cases, an audible hum.
Regulation 521.5.1 requires that where conductors enter a ferrous enclosure, they shall be arranged such that the conductors are only collectively surrounded by ferromagnetic material.
This requirement includes an SWA cable, but in this situation, where an additional protective conductor is required, it is permitted for the additional protective conductor to enter the ferrous enclosure individually.
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