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Consumer unit feed / main tails more than 3m

Hi, what are the requirements when a consumer unit is to be located where the mains tails are more than 3m from the cut-out? Quickly searching online it seems that a switched fuse unit (60A, 80A, 100A as applicable) is required after the meter? Does anyone know the regulation number in BS7671? Some have mentioned taking high voltage drop and Ze into consideration for a long run. Is SWA usually used? It is safer and could be buried in a wall if needed couldn't it? Mains tails are a bit dodgy anyway as contacting the line you could get the full PFC so I prefer the idea of the earthed armouring. 25mm 3-core SWA at CEF is about £13 per meter. I guess that's what happens in blocks of flats?

In this installation, the current position of the intake and CU is in the kitchen. They would like it moving under the stairs if possible which would mean a 5 or 6 meter run from the kitchen, up above ceiling, across and down into the under-stairs cupboard. I could potentially take an alternative route behind the kitchen units. Thanks.

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0 wallywombat over 3 years ago

3m is not a BS 7671 rule, it's a DNO rule. Basically the cut out fuse is there to protect their network, not the wiring in the house. Yes, people usually use a switch fuse near the meter. If its a long run, then Zs and voltage drop need to be taken into account, although this is unlikely to be an issue in practice unless things are already marginal.

SWA is probably a good idea, especially as the cable won't be RCD protected and is likely to be within range of a 50mm nail at various points. It does mean that you'll need an adaptable box or similar to terminate the SWA near the switch fuse.

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0 wallywombat over 3 years ago

3m is not a BS 7671 rule, it's a DNO rule. Basically the cut out fuse is there to protect their network, not the wiring in the house. Yes, people usually use a switch fuse near the meter. If its a long run, then Zs and voltage drop need to be taken into account, although this is unlikely to be an issue in practice unless things are already marginal.

SWA is probably a good idea, especially as the cable won't be RCD protected and is likely to be within range of a 50mm nail at various points. It does mean that you'll need an adaptable box or similar to terminate the SWA near the switch fuse.

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Consumer unit feed / main tails more than 3m

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