16mm tails won't fit in CU

[Miguel]

Hi everyone. Just wanted to make sure the wiring for my shower was safe before I started using it.

I have a 10.8kW shower fed with a 10mm^2 t&e. I have a 45A MCB in the CU, which in turn then goes inot a separate RCD also in the cupboard.

My original intention was to use 16mm tails to go between the CU and RCD and 10mm tail for the earth. However the largest cable I can get into the neutral at the CU is a 10mm tail.

I have now wired the RCD to the CU using 10mm tails and a 10mm earth (maybe overkill, but thats what I had).

I am assuming the 10mm tails will be ok? Also, what would be the recommended size to use for the earth?

thanks, Miguel

[Christian McArdle]

10mm will be fine. I'm surprised you couldn't fit 16mm in, though. The consumer units I've dealt will take 16mm into the earth and neutral.

Absolute minimum would be 6mm (the next size over half the live conductors).

Personally, I would have just used the same 10mm T&E that you have used for the rest of the run.

Christian.

[Dave Plowman (News)]

Think it's an *output* from a 45 amp MCB and the associated busses.

[Christian McArdle]

The MCBs for my consumer unit claim to take 25mm.

Christian.

[John Rumm]

They probably do, but what about the neutral bus bar?

[Christian McArdle]

16mm.

Christian.

[Miguel]

I have a Memera 3 by MEM. The live form the MCB will certainly take a

16mm cable, however the neutral bar is pretty tiny.

Just realised that my CU seems to be earthed via what looks like 4mm earth. The earth into the cupboard is larger however, so definitely going to get that fixed.

Thanks to everyone for their help

Miguel

Christian McArdle wrote:

[Andy Wade]

One technique is to divide the strands of the conductor into two groups (of three and four) and connect them into adjacent terminal positions on the neutral bar. (I'm not recommending that you do this, you understand, just saying that it is one technique.)

Probably 6 mm^2.

[The Natural Philosopher]

It is permissible to only insert MOST of the strands into the terminals. For two reasons.

1/. The proximity of a large busbar cools any localised heating.

2/. If the strands are cut very close to the busbar, the actual change in local resistance is minimised.

Cables are not specified to be able to handle the current without FUSING, they are specified to handle the current without excessive HEATING or voltage drop. You can put 15A through a single piece of 1mm dia copper just about..so there is plenty of cable capacity..its just a question of not overheating.

[Andy Wade]

I thought I'd not mention that old chestnut. Whatever you say (and I don't necessarily disagree with your technical argument) this is not regarded as good workmanship and isn't "permissible."

Doing it is likely to be regarded as a violation of regs:

• 133-01-01 Good workmanship & proper materials to be used.

• 133-01-02 Characteristics of equipment not to be impaired.

• 133-01-04 Every joint to be of proper construction.

• 133-01-05 Design temperatures not to be exceeded.