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Electrical

Submain RCD Protection

Anonymous user 23/02/2024 - 3.02 PM

A friend of mine has just had a extension built and has a 16mm t+e submain running from the existing supply cupboard to a big new board. I do have a couple of concerns you might be able to help me with. 1. The new board contains 2 cooker circuits, at leats 2 ringmains and a few lighting circuits, is the 16mm t+e large enough to carry this load? 2. The electrician has recommended a mem 100A switch with 60A fuse to protect the submain running through the house but should it have a 30mA time delayed RCD?

Are you a tradesperson and able to answer this question?

1 Answer

Proman Electrical Ltd

Rating: 5 out of 5

Swansea

Hi, The number of circuits is irrelevant. Fuses/MCB's protect cable not the appliances that are connected to final circuits. If the Fuse/MCB is too small and trips/blows to protect the cable then the cable is too small. Depending on length and how it is routed, 16mm may be okay. The type of additional protection will depend on the provided earthing system. a TT system requires that all circuits are RCD protected, using a 100mA Timed RCD to supply a submain that supplies a consumer unit with 30mA RCD's for final circuits is correct. With any other provided earthing system, you may not need the timed RCD depending on the current installation and earthing arrangement. Make sure you have an installation certificate and as important is to make sure that you will receive a compliance certificate from local building control. A registered electrician will notify on your behalf.

Answered11 April 2016