Consumer Units with RCBOs

[Tricky Dicky]

Screwfix have a BG 12 module CU with 6 RCBOs on offer for £69.99. At that price it is a steal so I am thinking of getting 2, one for the main house CU and I know it is overkill but one for the garage. I do want discrimination in the garage with 2 lighting circuits one for the main garage/workshop and one for the separated mancave, likewise 2 ring mains and all the outside lights will also be run off the garage CU.

The question is connecting the garage CU to the house CU? In the 17th edition wiki article the CU arrangement for a fully RCBO populated CU shows an MCB being used for the garage using SWA. In my case that will not be possible as the cable between CUs will be T&E with approx. 2m run in a wall chase. Is there any reason why the garage circuit cannot be protected by an RCBO at the house CU even though there will be further RCBOs for the separate garage/Mancave circuits?

Richard

[spuorgelgoog]

Yes, discrimination.

AFAICS no time-delay / 100mA RCDs are available as RCBOs, so you'd need to allow for a 2-module time-delay RCD and an MCB for the garage - if they're available in BG.

Also someone will hopefully clarify whether 100mA time-delay is acceptable for protecting buried cable.

Owain

[Robin]

sadly out of stock around here (well, the 6 nearest - I gave up at that point)

[dennis]

If it uses the same sort of RCBO it will probably trip if there is a fault on one of the garage circuits.

You need one that trips slower and/or higher leakage to avoid this.

[ARW]

It should be 30mA non time delayed.

Or make it a deviation from the regs and don't RCD it.

[Tricky Dicky]

Just checked the stock at Screwfix and none of the stores have any available so it's back to the drawing board. There is a similar one available at £99.99 with mini RCBOs but it gets a poor review from an electrician.

Richard

[John Rumm]

Yup, you will lose discrimination.

[spuorgelgoog]

If you don't mind an RCD board (with the option of some high integrity RCBOs) this is better than a steal

16 way dual RCD, your choice of MCBs, £50 inc.

Owain

[tony sayer]

Have TLC electrical not got any, we had a couple from them a while ago?

[spuorgelgoog]

Their 16 way only comes with 12 MCBs, their choice not yours, and is £68 + delivery + VAT.

Owain

[Robin]

Do you know what (if any) other brands fit Havell's boards? I was told they have pulled out of the UK market (so replacement MCBs etc might be hard to source).

[Tricky Dicky]

Apologies for resurecting this thread, but one final question. If I cannot have RCBOs at both ends of the garage supply, if I go for RCBOs in the garage CU and stick with am MCB in the main CU, does that MCB need to be outside of any RCD protected group or can it be RCD protected. There is a possibility that my garage supply cable can be re-routed under the floor and within cupboards or voids where none of it would require burial in a wall rather than the original plan which was to take it through the loft where at least 2m would have to be buried in a wall. I will not know how easy this will be until I lift a few boards and see.

Richard

[Archibald Tarquin Blenkinsopp]

Yes, No

Any difference between N and L current will trip an RCBO or RCD AB

[The Natural Philosopher]

My (limited) understanding is that it wouldnt NEED to be RCD protected but there is no requirement that it is *not* so protected.

[ARW]

The MCB should have NO RCD protection. Only the garage end should be RCD protected.

Did you know that if you bury the cable more than 5cm from the finished surface on the 2m run then it would not need RCD protection?

[dennis]

Or mechanical protection applied. steel conduit should require no extra protection.

[Fredxx]

I thought surface wiring was exempt too on the basis you're unlikely to poke a nail through a visible cable? Or is that only SWA?

[John Rumm]

Indeed.

No, that applies to T&E as well. (and surface wiring in trunking would also be ok for the same reason)

[John Rumm]

In this particular case there is, since the OP does not want to lose discrimination. If you have regular RCDs/RCBOs (i.e. non time delayed ones) at both head end and final circuit end, then you can't rely on one tripping in preference to the other.

[Fredxx]

That was my understanding but not sure if it changed under 18th ed. Of course a decorator might just sink the cable into the plaster and cover with PVC channelling!