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Dave Transformer

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Jun 2, 2023
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I'm looking to fit an SPD externally to the consumer unit, as there are no spare ways. The meter tails from the DNO connection box to the meter are 16 mm² CSA , approx. 150 mm long, then from the meter out of the meter box through the cavity wall and directly into the back of the consumer unit main switch. The tails are 25mm² CSA, approx. 1 metre long, so not externally accessible for a Henley box.

I was looking to connect an SPD unit directly onto the side of the consumer unit to the live side of the main switch to keep the connecting cables as short as possible.

With the short length and low risk of a short circuit with the interconnecting cables, I was looking for some guidance on conductor size, unless there was some operational reason for the cables to be a certain CSA size? The CPC is recommended as 6 mm² CSA. Thanks.
Some manufacturers say you can take the live from any circuit, it doesn't have to be a dedicated MCB. Others say no MCB required, amazingly, but pretty much all would agree that having some sort of isolation - in this case Main Switch - is a necessity. Have a look at surge devices website for more info on different connection option.