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Old February 5th 18, 02:18 PM posted to uk.d-i-y
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Default Adding RCBOs to Wyler Split Load CU

On Monday, February 5, 2018 at 1:28:04 PM UTC, John Rumm wrote:
On 05/02/2018 10:33, wrote:
Hi All,

I have a Wyler 12 way split load CU (NHrS12SL).

For various reasons, I will be having a qualified sparky do the work,
but wanted to check my options...

Currently our CU has most of the power circuits on the RCD side, and
3 lighting circuits (which could maybe be reduced to 2 (combine the 2
downstairs circuits into 1 (it’s not a mansion). And the immersion is
also on the non RCD side.

I am thinking it is time to give at least the lighting circuits RCD
protection, but would like to avoid the cost of a new Box (which
would allow 2 RCDs).

Any particular reason for wanting to change?

The electrican who has been making ammendments to one of the existing lighting circuits saus that he HAS to put it on RCD in order for it to be regs compliant.

I wondereed about doing all the lighting circuits while I was about it. Wylex "say" that all circuts run under plaster should be RCD protected (well, they would wouldn't they), and if possible I'd rather not have all the lights go out together, so a bunch of RCBOs on the non RCD side seems attractive.

Lighting circuits generally
pose a very low shock risk, so the benefit from a RCD is limited for
that application.

Could this be done by replacing the MCBs on the non-RCD side with


and could these be as slim as the existing MCBs? Or would it
need the double width type?

Wylex do single module RCBOs, so as long as there is enough height in
that CU (RCBOs are taller than MCBs) you should be fine.

Any suggestions as to which circuits to put where (without doing too
much messing, or we might as well go for a new box). Current setup is
3 power radials, one ring main, cooker and a spare 32 A (which might
eventually feed a second mini ring for the kitchen) on the RCD side,
and as noted above, 3 lighting and 1 immersion heater on the

If I were adding anything, I would do a RCBO on the non RCD side for the
kitchen, and leave the rest as it is.



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Cheers John