To RCD protect or not to RCD protect (a hopefully simple question)?

[Seri]

My new boiler arrived today (feelings of happiness mixed with feelings of emptiness in the wallet department). As I was studying the wall that is to be its new home and making sure my original designs would be accurate I realised I'd missed an area when hatching my master plan. I'm currently rewiring this house one room at a time. In the kitchen I plan on having the only non RCD protected socket in the property (for the freezer so if the RCD trips whilst on holiday the contents won't spoil).

Questions: Should the boiler be RCD protected or not (any pro's and con's?) If the boiler shouldn't be RCD protected then is it okay to have it on the same spur as the Freezer? If the boiler can be on the same spur as the freezer then will I need to convert that spur into a ring? If the boiler should be on its own circuit, what rating MCB should generally be fitted?

Thanks for any answers, as ever, it's all appreciated.

Seri

[Lurch]

On Wed, 19 May 2004 10:21:45 GMT, in uk.d-i-y "Seri" strung together this:

No, the only sockets\fittings that need RCD protection are ones that are likely to supply portable equipment used outdoors. It has the same pros and cons as the freezer, you don't lose heating or hat water if the RCD trips.

Yes.

No, you can run two radials from one MCB. A 16A MCB with 2.5mm cables is ample.

If it was on it's own circuit, then I would fit anything from a 3A MCB upwards, and appropriate cabling to suit.

[Christian McArdle]

Put it off a 3A FCU off an existing circuit, or off a 3A MCB on its own circuit. RCD protection is optional, but preferably not. The disadvantage is that you lose heating in the event of a trip, which may lead to pipes freezing if you're off skiing in January.

Yes, that's fine. The freezer and heating won't use anywhere near the 16A MCB that would be expected on such a circuit.

No. Just take a 2.5mm cable from the freezer socket to the FCU. After the FCU (with 3A fuse), you can run in 1mm lighting cable. In fact, you can probably use less than 2.5mm to the FCU, but this would require calculation and there really isn't much point.

3A if you choose to run on a dedicated circuit. Personally, mine runs off a 3A FCU on a 16A MCB circuit shared with the immersion heater. This enables combined controls and the safety of knowing that all parts of the central heating system are on the same circuit.

Christian.

[Tony Bryer]

Having the CH on its own circuit is the best arrangement IMO, so that if the main ring is off (either deliberately or as a result of a fault elsewhere) the heating is not affected. You need to ensure that you have an isolating switch that isolates all the heating. 5A and 1.0/1.5 cable should be all you need.

[usenet]

There's no regulations requirement for it to be RCD protected and I don't really see any good reason for doing so.

Yes, why not.

No, why on earth would you need/want to do that?

Probably needs only a very small current so a 6 amp would do, size the wire to match.

However my feeling would be to use the same circuit as for the freezer, wire it with 2.5sq mm and have a 20amp MCB. It's then a 'conventional' radial circuit as in the IEE On-Site Guide. The boiler should have some means of isolating it, a double pole switch or use a socket.

[Lurch]

On 19 May 2004 12:45:01 GMT, in uk.d-i-y [e-mail] strung together this:

16A is better as 20A needs calculating correctly and quite often needs a smaller MCB or bigger cable.

And a fuse, 3A usually. So a switched fused spur then.

Only if it's a switched socket, you shouldn't be able to remove the socket while it's 'on-load'.

[Christian McArdle]

And a DP switched socket at that!

Christian.

[Lurch]

On Wed, 19 May 2004 15:00:00 +0100, in uk.d-i-y "Christian McArdle" strung together this:

No, a SP will do. The functional switching of the supply will be done by the switch on the socket and the isolation is done when the plug is removed from the socket. Although a DP switched socket would be better.

[Christian McArdle]

I was under the impression that SP switches weren't allowed for fixed appliances in case someone mistakenly used the SP switch for isolation rather than pulling the plug out. Possibly more of a best practice thing than a specific regulation, though, I suppose.

Christian.

[Lurch]

On Wed, 19 May 2004 15:31:32 +0100, in uk.d-i-y "Christian McArdle" strung together this:

That's why you usually use a DP switch for fixed appliances, and plugs and sockets for portable appliances. Although you are right in a way.

[ARWadsworth]

I thought it was a choice of double pole switch (or DP FCU), double pole switched socket or unswitched socket for fixed appliances. Many fixed appliances such as cooker extractor hoods come with a moulded plug but they do state double pole switched sockets or unswitched sockets must be used.

Lurch if I may ask a quick question, you said

Only if it's a switched socket, you shouldn't be able to remove the socket while it's 'on-load'.

What do I do about my iron? I know it is a portable appliance but there is no on off switch on it and if it was used on an unswitched socket I must always insert and remove it under load. Are some appliances banned from unswitched sockets.

Adam

[Lurch]

On Wed, 19 May 2004 18:15:34 GMT, in uk.d-i-y "ARWadsworth" strung together this:

Can't say as I've ever read the instructions TBH, but see the response below, I think that answers this question as well.

That's why you're meant to have switched sockets. Unswitched sockets are for where there are other means of switching, e.g. a switch fuse above the worktop with an unswitched socket below.

[ARWadsworth]

But there is no requirement AFAIK for switched sockets (but I always fit them), only a requirement for DP switched sockets if an appliance is fixed (or an unswitched socket or DP switch feed to an unswitched socket) as it is the double dole isolation that is required.

It was the point you made about a loaded circuit not being allowed to be unplugged that I was curious about as it would be impossible with some appliances.

Adam

[Lurch]

On Wed, 19 May 2004 19:33:12 GMT, in uk.d-i-y "ARWadsworth" strung together this:

I seemed to think there was, maybe I'm mistaken but it sounds sensible.

I was referring to correctly wired installations, if there isn't a switch to functionally turn of the supply to the socket then you're right, you can't unplug an appliance 'off-load'. This is why you need to have things done properly.

[Z]

In article , Seri writes

If you can put the boiler on it's own circuit to minimise the disruption caused by an interruption elsewhere. 16A breaker 2.5mm cable or 1.5 Pirelli terminating in a switched fused spur with /without neon as per your preference. No reason to RCD protect the central heating in fact one might get nuisance tripping if RCD protected. I get pretty sick in winter of calling out the the central heating contractors to look at GCH systems which are tripping the RCD protected side of split load consumer units.

[usenet]

I'm unconvinced by this, a 2.5sq mm radial on a 20 amp MCB is no nearer to 'needing calculation' than a 2.5sq mm ring on a 32 amp MCB is it?

Why the fuse? If the boiler installation instructions demand it then yes but it's surely not a 'generic' requirement of any permanently wired equipment is it?

That's a new one on me, is there an IEE regulations requirement that states this?

[usenet]

Yes, surely this is to make sure that the person disconnecting the device really does disconnect it and doesn't (by mistake) rely on a single pole switch.

[Seri]

| writes | >My new boiler arrived today | >Should the boiler be RCD protected or not (any pro's and con's?)

Just wanted to say thanks to everyone for responding and I will be running the boiler from a dedicated MCB on the non RCD protected side of the CU.

Really appreciated.

Seri

[Lurch]

On 20 May 2004 08:30:49 GMT, in uk.d-i-y [e-mail] strung together this:

Well, I don't generally fit any 2.5mm radials with 20A MCB's unless they're relatively short\exposed runs. I'll look into that though, it's just the way I've always done it and I seem to think I did have some theory behind it once!

So you'd fit a boiler to a DP switch with only a 16\20A MCB as protection would you? I haven't come across a domestic boiler yet that doesn't state "use a 3A fuse". However, I was only referring to this particular appliance, it wasn't a generic requirement. If the CPD is sized correctly to be able to offer overload protection to the appliance then a DP switch is all that is required.

I seem to think there is, buggered if I can find it though! It's probably written in such a way that it's doesn't mean that until you've read it half a dozen times.

[usenet]

Who are 'they'? A radial wired in 2.5sq mm protected by a 20 amp MCB is one of the 'conventional circuits' for BS1363 sockets listed in the appendices of the IEE "On-site guide". It's only the wierd insistence on ring circuits in this country that means radials are not so widely used, in some situations a radial makes much more sense than a ring.

Which is basically what I was saying, I think.

Anyone else any ideas?