Consumer Unit RCDs

AdamCH · 30 Sep 2007

Hi

Probably a stupid question but I'll ask anyway.

I'm looking at having the main consumer unit replaced with one with more circuits & RCD protection. I was looking at the Wylex kit that screwfix sell - 10 MCBs + double pole 80A 30mA RCD.

Question I have is does the RCD protect all the circuits or does it just protect one circuit?

Many thanks
Adam

Jaymack · 30 Sep 2007

This particular unit has copper "combs" for the common connection of the mcb's to the circuits - these are: -
1. Non-RCD protected circits such as lightiing and: -
2. RCD protected for socket outlets and showers etc.
These combs are cut to suit the user's particular requirements for the allocation of the circuits and spare ways. A 30mA RCD is used for personal protection; and where you have a TT supply, another RCD is required as a main circuit breaker; but time delayed and rated 100mA - this is used to reduce the risk for damage to property and/or livestock. I think there are diagrams, which show the different types of main supply under faq's on this siite.

AdamCH · 30 Sep 2007

Thanks

The one I was looking at is:

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331831&ts=59910&id=28504#

If I've understood you right, the circuits to the left of the RCD are protected by the RCD & the ones on the right aren't?

& the placement of the RCD is fixed?

Thanks
Adam

AdamCH · 30 Sep 2007

If I wanted all of the circuits to be covered by the RCD should I be looking at something like:

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331831&ts=60702&id=22596

Where the DP switch is replaced by an RCD?

Many Thanks
Adam

Spark123 · 30 Sep 2007

Why would you want all the circuits to be RCD protected by one RCD? Who will be replacing it?

AdamCH · 30 Sep 2007

I'd be getting an electrician in to fit it. I wouldn't fancy playing with the meter tails even if I was allowed to.

So rather than have the whole board shut off if the RCD tripped I'd be better off with RCBOs like this one:

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331832&ts=61243&id=27903

Fitted to each individual circuit? So that only one trips at a time?

Do any of the consumer units take RCBOs or is it only certain types?

Thanks
Adam

Spark123 · 30 Sep 2007

Although RCBOs are better it will cost an arm and a leg. You don't really want all the circuits on one RCD as a faulty appliance will kill your lights and leave you in darkness! If you are going to have an electrician fit it then it may be better left to him which one to buy.

RF Lighting · 30 Sep 2007

Why don't you let your electrician supply a CU he is familiar with fitting, and he has decided is the right sort for your installation?

AdamCH · 30 Sep 2007

If cost were no object then a board full of RCBOs would be best? or are their disadvantages?

RF Lighting · 30 Sep 2007

There is no need to RCD protect all your circuits.

But yes it is best to use RCBOs on the circuits which do require protection. (but cost often prohibits this)

AdamCH · 30 Sep 2007

Thanks,

Which circuits wouldn't you cover with an RCD? I'd assumed if it was good for one then it would be good for all.

ack351 · 30 Sep 2007

Fitting the cooker circuit with RCD can be a bit of a pain in the wotsits, the element in your oven with be susceptable to earth leakage and may trip the rcd on a regular basis. Then if you've got your lights on rcd protection you'll be left in darkness.

Steve · 30 Sep 2007

AdamCH said:
Thanks,

Which circuits wouldn't you cover with an RCD? I'd assumed if it was good for one then it would be good for all.

- Lighting (safety)
- Refrigerators (so your food wont defrost, and because fridge motors are prone to harmless earth leakage)
- Ovens (again, heating elements prone to harmless earth faults)
- Any major appliance with a motor or large heating element.

Many homes now have a dedicated refrigeration circuit.

The regulations only require "sockets that can reasonably be expected to provide power outdoors" to be RCD protected. Most electricians will RCD protect showers, and all sockets, and any outdoor circuits (outdoor lights on a lighting circuit excepted - no protection required).

AdamCH · 30 Sep 2007

Ok thanks for all that info, it's very helpful.

Fridge is on the same ring as the rest of the kitchen circuit so I'd need to leave them off the RCD.

No problem leaving the Oven off.

One thing I don't understand - why is it safer to not have the lights go out than to get electrocuted sticking my fingers in the light socket? Or will the fuse protect me anyway?

Btw would I put the burglar alarm on or off an RCD?

Thanks again
Adam

Steve · 30 Sep 2007

AdamCH said:
Fridge is on the same ring as the rest of the kitchen circuit so I'd need to leave them off the RCD.

No, dont do this. Your kitchen sockets are likely to be able to feed equipment outdoors. Its not essential that your fridge isn't RCD'd, but preferable. How easy would it be to run a seperate feed to it? If not, dont worry about it. Our fridge freezer is on an RCD, and the compressor in that thing is really very noisy and draws a huge startup current. Only older appliances tend to cause trouble.

AdamCH said:
No problem leaving the Oven off.

As long as theres no socket on the cooker control unit! Could provide power outdoors! Swap it if possible.

AdamCH said:
One thing I don't understand - why is it safer to not have the lights go out than to get electrocuted sticking my fingers in the light socket? Or will the fuse protect me anyway?

The fuse or MCB wont stop you getting killed from your own stupidity. It takes 50mA to kill someone. It is generally accepted that people dont go taking bulbs out and poking their fingers in there. And it is also accepted that people working on the lighting circuit will turn off the MCB and lock it off to start with!

AdamCH said:
Btw would I put the burglar alarm on or off an RCD?

OFF! Preferably on its own circuit, again.

You'll gather here, that replacing the consumer unit often entails adding new circuits, it is the ideal time. If you do buy the consumer unit, buy one thats way too big, say 4 extra ways.

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Consumer Unit RCDs

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