30mA. 'Additional' RCDs come with a warning about disconnecting before performing earth testing..."/>

R C Ds

I've just fitted a split load consumer unit, and have a couple of RCDs that are no longer needed. Does it effect the operation in any way to have two in circuit - ie the one in the CU and an RCD socket on a ring that is now fed by it?
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Hitting the 'test' button on the downstream one may in some cases trip the upstream one too. It will always be at least as safe, and in the event of one of them failing, will still provide protection.
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Wot U doin with the old RCD's?..
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On Tue, 24 Aug 2004 22:19:41 +0100, Dave Plowman (News) wrote:

Assuming both are 30mA non-delayed devices you lose discrimination as to which will trip in the event of a fault, ideally you shouldn't cascade RCDs for this reason. Chances are the one nearest the supply will trip first as it will also be seeing the leakage on all the other circuits fed from it.
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In my experience, they normally both trip. Unlike fuses and MCB's, the amount by which you exceed the trip current doesn't seem to have much effect on the trip time.
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As long as I'm not compromising safety issues.
The ones in question feed outside sockets which are only used occasionally, and if they tripped the main one as well, I'd be no worse off, as it were.
They're flush mounted FCU types, so if I removed them I'd have to fit a blank plate etc.
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Depends on what else is fed by the same ring, and that you realised promptly that it had tripped (and did something about it).
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It's a split load unit, and I've fed everything I can off the RCD. Only things not are the oven, immersion, alarm, and utility room ring.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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And the lights, I hope?
Christian.
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wrote:

I'd take the lighting off the rcd, RCDing that creates more risk than it solves.
Regards, NT
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It would be easy enough to do, but I'm going to see what happens.
The old 8-Way CU with rewirable fuses has only once blown a fuse - and that was the immersion heater.
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On Thu, 26 Aug 2004 00:16:40 +0100, Dave Plowman (News) wrote:

Ho ho, or not as the case may be. The point about taking the lighting off the RCD is so that the whole household is not plunged into darkness when someone does something stupid up a ladder or with a drill or simply a faulty flex.

RCDs are not overload devices as I'm sure you are aware and fuses take a considerable overload to blow anything like quickly. 30mA leakage is not a great deal, especially if you have much computer(*) kit running through it. Surges and other supply quirks can trip an RCD as well.
(*) Stuff with switched mode PSUs, with lots of suppression stuff on the mains side.
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Well, at the moment the whole household consists of me. ;-) And if you're fiddling with a live circuit where this could happen, isn't the whole point of the RCD to protect you from injury? Like say changing a bulb?
I realise what you're saying, but remember this is London where it's never pitch black.

I was just making the point that I don't often have circuit failures of any sort.

The computer stuff is already on a radial with its own RCD - as is the Hi-Fi. And they've never tripped either. ;-)
The more I think about it, the more it would make sense to have one RCD per circuit.
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On Thu, 26 Aug 2004 09:16:20 +0100, Dave Plowman (News) wrote:

Never any visitors, helpers or trades people?

Are your light sockets live when switched off?

He he, unlike up here where a cloudy night is absolutely, completely and utterly dark, with the possible small exception for a week or two around midsummers day. Even then it would be pitch black inside most of the house apart from the north facing rooms.

But you have only been "detecting" serious overloads in the past not small leakages. That immersion that failed may well have started to cause the odd RCD trip for quite a period before it failed short. OK the immersion is not RCD protected but it serves to illustrate.

This is probably the best way to go but RCBOs aren't cheap...
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That's the best solution, but not cheap. It is done using RCBOs, which combine the RCD functionality with the MCB. I use them in my installation, but many would baulk at the cost.
Christian.
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wrote:> > > It's a split load unit, and I've fed everything I can off the RCD.

should be pretty easy to figure out :)

rcd trips are way more common of course. Hope you never have a fire, you could bitterly regret your lights being on the rcd.
Regards, NT
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Why?....
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solves.
Because very few people are killed or injured from faults in the lighting circuit, whilst loads of people are killed or injured when the lights go out unexpectedly when in a dangerous position, or they can't find their way out in a fire which has caused a whole house RCD to trip, taking out the lighting.
Christian.
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Well I've known and heard of more incidents with lights and electric shock then lights tripping in a house fire. But I suppose your mileage may differ.
And I wonder what the changes of a house fire tripping the RCD is unless the RCD tripped before the house fire started?.....
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The design of lighting sockets means that it is very difficult to get much more than embarassment from the attendent shock of sticking your fingers in.

Quite high when the fire starts burning through the cable insulation.
Christian.
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