Will one RCD socket protect others??

[Mark]

Some time ago I fitted a new socket outlet in my son's bedroom. I had no desire to go into the wall and hook into the existing ring main so I decided to tap in somewhere else. Basically I tapped into the immersion heater supply in the airing cupboard, (fused 30amp at the consumer unit). Then I went through a 13amp fused spur, then up into the attic, and then down into the bedroom using mini trunking, and finally connected an RCD protected double socket. Everything fine.

Now I need to do the same in my daughter's room. My question is, if I wire in parallel from the feed to the socket in my son's room do I need to use another RCD protected socket? Or will the RCD in my son's room provide protection for a regular parallel socket.

Safety is paramount of course but I don't want to spend 20 odd quid on another RCD socket if I don't need to.

Incidentally the sockets are only for hi-fi/TV so I doubt the combined load will ever exceed 5 amps.

Thanks

[john]

Single 2.5mm cable is only rated at 23 amps. The immersion circuit should be on a 16 amp mcb.with no other supply taken from it !

[ARWadsworth]

Years ago (and I am not grey haired yet) when I was a child my Dad put another socket in my bedroom for the TV I got as an Xmas present. It was one of the things I failed his PIR this week as this socket ran from the immersion. He wants to sell his house and I will have to work like hell over Xmas to put the electrics right due to these type of bodges.

Do the job properly or not at all. Break into the ring main.

Adam

[Sparks]

What size cable is this circuit using - 4mm or more I hope, if it is 2.5mm you need to replace the 30A MCB with a 20A one, unless the immersion is on it's own 2.5mm ring.

If you have an immersion, I hope this is connected with an FCU, fused at 13A (Unless you have the unlikely scenario of an immersion heater greater than

3KW)

Possibly fine, if the immersion heater cable is 4mm (or more) or on a 2.5mm ring.

Unless the socket in your son's room has a dedicated RCD protected output, and you use this, you need another RCD socket, or just replace the fused spur with one of these.

(Then any further additions will be protected)

If you just connect a normal socket to the same terminals the existing socket is being supplied with, it will not be protected.

This is irrelevant, you are providing a 13A socket, it needs to be able to support this load - someone may plug in a heater at some point.

Sparks... (Not an electrician)

[Mark]

Sorry my mistake, the immersion heater is on a 16 amp mcb, it's the electric oven that's on a 30 amp mcb.

We haven't used the immersion heater in 8 years and have no intention of doing so, so as far as I'm concerned it's a spare supply. In the event we have to use it in an emergency then the spur I've taken of it will be switched off.

[Mark]

Thanks for your reply.

My mistake, the immersion is on a 16A mcb, it's the electric cooker supply that's on a 30amp mcb.

Yes the immersion has its own FCU in the airing cupboard with a 13amp fuse

Thanks for the recommendation

Why not? Isn't the RCD measuring earth leakage irrespective as to whether something is plugged in 'in front of it' or 'behind it'?

Yes, and if the load is over 13amps the fuse in the spur blows, I don't see a problem here as long as the cable itself is correctly rated?

[Mark]

Sorry, did you intend to answer my question or just lecture me on what you consider to be the correct way to do the job?

Shouldn't you be in the airing cupboard fixing the "bodge"?

[Sparks]

If that were the case, your whole house and all the people on the same phase as you would be protected by your RCD socket.

The socket is measuring the differance in current at it's output, it can't control what goes into it. - are you sure you should be messing with this, no offence, but you don't sound like you should be.

There may be some regulations about not being able to apply diversity to circuits with fixed loads on (The heater in this case) but I don't know, I wouldn't do it this way myself, unless the heater was decommisioned.

With your immersian heater on, assuming it is 3KW, you only have 3A (700w) of spare capacity before the MCB is at it's marked limit - You can probably uprate this MCB to a 20A, but this still only allows 7A with all at full chat. ...and it doesn't sound like you should be poking about in the consumer unit anyway!

The ideal way to do it is to either tap into an existing ring (Only one double socet per tapping, unless you fit a spur in-between, then you can fit as manu as you like downstream) or run a new circuit from the consumer unit.

Part P will apply.

Sparks... (Not an electrician)

[Sparks]

If "ARWadsworth" is doing a PIR, then he is probably a qualified electrician, so his "lecture" as you put it, is not necessarily the way he "consider[s] to be the correct way to do the job" but may well be the legal way to do so.

By your comments earlier, it does sound like you should either leave it alone and get a qualified electrician to do it, or just ask questions BEFORE you start, and only tackle the job once you are confident you have learned all you need to know to complete the job safely.

Throwing a strop when someone suggests what you have posted is wrong, is not going the right way towards getting help.

Sparks...

[Mark]

OK, additional RCD socket it is then.

Thanks for your input.

PS, should have mentioned, immersion heater is never used, never has been, never will be.

[Sparks]

Good

Disconnect it then, then everyone will be happy and you will (probably) be compliant. (Assuming you have sleeved the earth wires with green/yellow, stuck one of these on your consumer unit if you are using new colours

and used 2.5mm cable without any inaccessible screw joints. (Maybe some other factors too)

Sparks...

[Sparks]

...and I would suggest you replace the spur with an RCD one rather than getting a second RCD socket, then if you add another socket to this circuit at a later date, you won't need to buy a third RCD socket.

As the new sockets are protected with a fused spur, you can add as many sockets as you like, where you like, so you can just add a second double socket to each room, off of the current socket, to save having to use trailing extension leads, if you leave the FCU as it is, any additional sockets would need to be the expensive RCD ones (If you want to RCD protect them, as it is not actually needed, assuming you are upstairs)

Or, if you change the power source at a later date to come from the ring (like it really should) then you won't have to remove the RCD sockets (assuming your ring is currently RCD protected)

If you do change the FCU to an RCD FCU, you should replace the current RCD socket with a normal one, as you shouldn't cascade RCD's)

Sparks...

[John Rumm]

27A if surface wired. However in the case overload protection would be provided by the 13A fused spur. In spite of the high sounding rating, fault protection for the 2.5mm T&E would probably be provided by the 30A fuse at the CU (although one ought to do the calculations to prove it)

That would depend on the size of the immersion heater(s).

Ideally, but suitably labled at the CU this would not be a big problem

[John Rumm]

What exactly are you trying to achieve here? Is it a case you have young children and you are worried they might go sticking conductive things in sockets? Or is there some other motivation? Other than the RCD protected socket you added, are there no other sockets in the room?

Perhaps you ought to be looking at the broader picture, and changing your system to include RCD protection for *all* the sockets in your house - especially those that may be used to power appliances used outside. This would need to be done at the consumer unit end of things.

Grafting on individualy protected sockets does sound like a hard way to do it.

If you have no plans to ever use the immersion heater, then you could simply disconnect it and re-designate the circuit. If you changed its MCB for a 30mA trip 20A type B RCBO, then you could use that cable as a radial circuit to supply a number of sockets as and where you need them. These sockets would then all have RCD protection. Perhaps you might be better off looking at getting the CU changed for a split load unit so you could have all socket circuite RCD protected.

[bob watkinson]

Mark, me old son, everything about your postings scream at me that you haven't got a scoobydo what you're talking about. You even dismiss with contempt the advice freely given by A R Wadsworth, a qualified sparky who is telling you succinctly how the job should be done. Do yourself a favour and get in a proper sparky. You really have no idea just how little you know.

[Mark]

OK that makes sense, I'll fit an RCD spur instead.

Thanks again

[Mark]

Bob me old mate. As it happens I have a degree in electronics engineering so I do feel I'm qualified to go 'poking about' in my consumer unit. Just that I never bothered to find out how an RCD works. Now I've located a circuit diagram of the inside of an RCD it is clear to me that it will only protect loads connected downstream of it. In the course of my work I have frequently suffered the cowboy bodges of so called 'proper' sparkies in the factory environment where H&S is paramount. In fact one nearly killed me when he assured me he had isolated a circuit and it turned out he hadn't. So I tend to have a healthy disrespect for 'proper' sparkies until they have demonstrated the quality of their work to me. I also assume it was a 'proper' sparky who wired my house in the first place (new build) and didn't tighten the screws in the back of two sockets resulting in them burning out when first used with a high load. So please don't lecture me about using professionals. I imagine many of the posters in this group are into DIY, not because they want to save money or derive pleasure from it, but because they want the job done right the first time around.

Regarding the advice from A R Wadsworth, it was worth what I paid for it. He is typical of many in newsgroups who seek to get on their soapbox and berate and patronise posters rather than try to educate and impart knowledge. Had someone simply answered my question and explained how an RCD worked then it would have been job done.

[Andy Dingley]

To give you the simple answer you obviously want, then No!

Years ago, voltage-activated ELCBs were sometimes used. In some cases, these might have triggered owing to a fault current in the way you describe (but not to an extent you'd want to rely on).

Today though, we use RCCDs that work by detecting currents and they will only do it for "downstream" devices.

[bob watkinson]

Perhaps, but you are the most dangerous type of bodger there is. The type who actually believe their knowledge is greater than a specialist. On you go mate, you've torn up the regulations and don't care whether or not you kill anyone. Why ask advice anyhow if you don't like the answer?

[Aidan Karley]

You're going to cut it out and burn it after you're dead under the Clapham Omnibus and your grieving family sell the house to Elmer Fudd, whose brother is a personal liability lawyer. If it can go wrong, it will. At the most inconvenient possible time and in the most inconvenient possible manner.