N. Foster asks about what regulation a particular wiring method might contravene. His question has been answered by SELECT (Theme – Regulations & Legislation):
Question: I work with an electrician who supplies single-phase socket outlets via a three-phase MCB (20A) using a five-core 4mm cable terminated into a joint box and then 2.5mm three-core to each outlet.
He insists that it is a legal method of wiring. I am sure it is not (borrowed neutral if nothing else; also circuit separation issues).
What regulation does it break, and if he was to use single-phase MCB on the five-core cable (three off) would it breach a different regulation?
Answer: The circuits supplying the single-phase socket- outlets should preferably be protected by single phase circuit protective devices.
Regulation 314.2 requires that separate circuits are provided for parts of the installation which need to be separately controlled in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of a single protective device.
In the event of a fault on one these circuits the TP & N breaker will operate and all three circuits will be disconnected, which could lead to an inconvenience.
I note there is no mention of additional protection of these socket-outlets by 30mA RCD.
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