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Flakey 16mm sub main

It's a 70's property, TT, extended in 2011. They obviously took one look at the ancient Wylex fuse board and decided to split the tails in a Henley and run a 16mm t&e sub main into a new split board supplying the extension.

The water and gas bonds 10mm, yet to be verified, go into the extension board and I've been asked to replace the original board. British gas have installed two new rods (600mm apart?!).

So, the way in which the sub main is installed is non compliant, exposed cores etc, and in my opinion the tails should be split into a switch fuse and the 16mm run from there. I'm thinking that RCD protection can be omitted as the 16mm runs in stud walls and under the floor.

This is an ugly job and I don't like it but I don't want my prejudices to incur additional cost for the client. So am I right in thinking that the 6mm cpc in the t&e is sufficient for the earthing and bonding for the replacement board (as it's TT) and can I just replace the old Wylex board and leave the flakey sub main as is?

Furthermore, if the 16mm t&e did run <50mm and required RCD then how would that work? Is the answer don't run t&e in those circumstances?

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0 Sparkingchip over 5 years ago

mapj1:

But you are replacing the old hot wire board, give the sub-main a 50A RCBO in that and satisfy the single point of isolation requirement at the same time.

A double pole 100 mA S-Type RCD main switch in the first consumer unit with the distribution circuit to the second consumer unit on a MCB, then the second consumer unit can be split with two double pole 30 mA RCDs or have DP RCBOs, as can the first consumer unit for the final circuits.

I would consider that to be sensible, but the RCD main switch may have to come out of the consumer unit and go into the tails upfront of the CU, because devices may have to be mixed and matched from different manufacturers if you use Type A RCDs.

I have some Schneider 300 mA RCDs in stock with one on the van plus one of another make, though I cannot remember which make off hand, but it has a matching 63 amp MCB with it just in case it’s needed. Those be installed alongside other manufacturers devices in the same enclosure on the same busbar as they won’t line up correctly, so would need to go in their own enclosure on their own busbar.

It is much easier when all the devices are from the same manufacturer and can go into the same enclosure, but that is not how it seems to work at the moment.

Andy Betteridge
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0 Sparkingchip over 5 years ago

mapj1:

But you are replacing the old hot wire board, give the sub-main a 50A RCBO in that and satisfy the single point of isolation requirement at the same time.

A double pole 100 mA S-Type RCD main switch in the first consumer unit with the distribution circuit to the second consumer unit on a MCB, then the second consumer unit can be split with two double pole 30 mA RCDs or have DP RCBOs, as can the first consumer unit for the final circuits.

I would consider that to be sensible, but the RCD main switch may have to come out of the consumer unit and go into the tails upfront of the CU, because devices may have to be mixed and matched from different manufacturers if you use Type A RCDs.

I have some Schneider 300 mA RCDs in stock with one on the van plus one of another make, though I cannot remember which make off hand, but it has a matching 63 amp MCB with it just in case it’s needed. Those be installed alongside other manufacturers devices in the same enclosure on the same busbar as they won’t line up correctly, so would need to go in their own enclosure on their own busbar.

It is much easier when all the devices are from the same manufacturer and can go into the same enclosure, but that is not how it seems to work at the moment.

Andy Betteridge
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Flakey 16mm sub main

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