overlapping ring and radial 13A circuits

[the yorkshire dalesman]

Is it permissible to have 13A sockets on 2 different ring, (or a ring and a radial) circuits serving the same area of the house? What prompts this post is that IIRC it is standard advice that all downstairs 13A sockets should be on an RCD circuit.

What I should like is to put sockets for electronics (computers, TVs, clock radios etc) on separate circuit(s) to those used for kit which is likely to trip RCDs. There would be 1 or 2 double 13A sockets on this ring or radial in most rooms. I get a fair amount of tripping from portable outdoor kit like hedgecutters - portable workshop tools (sanders, planers etc) are another bane. So the 'electronic' sockets would be run through a normal switch & cartridge fuse or MCB & definitely nowhere near an RCD. The sockets would be suitably marked & possibly be coloured (I've seen coloured 13A sockets - presumably they are easily obtainable?). So is it possible to install this scheme within the regs?

TIA

[usenet]

Yes, I don't think the wiring regulations say anything at all about whether sockets in a room (or area) have to be supplied by a single MCB.

There might be issues with different phases but that rarely applies in a domestic supply.

[Owain]

"the yorkshire dalesman" wrote | Is it permissible to have 13A sockets on 2 different ring, | (or a ring and a radial) circuits serving the same area | of the house?

I think it is a rather sensible idea actually; it means that if one ring is down you have somewhere close by to plug in the inspection lamp / hot air gun / radio / teasmade / whatever.

The two caveats are:

1. Phase separation - unlikely to arise in a domestic dwelling which are normally not supplied 3-phase.

1. Clear labelling of circuits at the CU ot prevent confusion.

| What prompts this post is that IIRC it | is standard advice that all downstairs 13A sockets should | be on an RCD circuit.

That is because there is the possibility they may be used for outdoor equipment. Sockets which 'may' be used to power outdoor stuff MUST be RCD protected.

| What I should like is to put sockets for electronics (computers, TVs, | clock radios etc) on separate circuit(s) to those used for kit which | is likely to trip RCDs. There would be 1 or 2 double 13A sockets on | this ring or radial in most rooms. I get a fair amount of tripping | from portable outdoor kit like hedgecutters - portable workshop tools | (sanders, planers etc) are another bane. So the 'electronic' sockets | would be run through a normal switch & cartridge fuse or MCB & | definitely nowhere near an RCD.

Whether or not you require RCD on sockets will depend on your installation and its earth arrangements. If you require RCD protection to comply with the disconnection time of 0.4s on a socket, you cannot omit that simply because you want to plug your clock radio in.

The best thing to do would be to install dedicated circuits for your outdoor and workshop sockets which do not run through the same RCD as your house sockets but have their own RCD protection.

If you have a split load CU, you could take a supply using a spare circuit on the non-RCD side to individual RCD-protected sockets or a new RCD for that circuit only.

If you have a whole-house RCD, this should really be replaced as it is unsafe (a fault in your workshop could leave you without lights and with a power tool spinning down).

Owain

[Christian McArdle]

You can. However, if your current installation is prone to tripping, then something is wrong. You may find you have an appliance with a latent earth fault, or a neutral/earth short somewhere. This should be fixed, rather than bodged around, trying to find excuses not to have RCDs on sockets. Quite frankly, all your socket circuits should have RCD protection, whether required by regs or not. This is PARTICULARLY the case for anything that is likely to see power tools. The only exceptions are special circuits for systems that you don't want to fail when you are out, such as a dedicated fridge/freezer circuit, or your central heating. You should install a separate dedicated outside socket on its own 16A RCBO (or 16A MCB with RCD built into socket). Your leaky hedge trimmers then get the benefit of RCD protection without causing your computer to shut down when you cut the cable, or get it wet. If you have a workshop in the attached garage, this should have its own RCD protection from the rest of the house.

If you simply have too much equipment connected, then rather than installing lots of cable into complex arrangements, which is expensive in terms of time, I'd upgrade the consumer unit to something more tolerant. The best solution here is to use a simple isolated consumer unit (not RCD or split load) and use B32/0.03A RCBOs for socket circuits. This way, leakage on one circuit won't make another circuit oversensitive to any increase in leakage current.

Christian.

[northern_relayer]

many thanks for advice, Owain (& Christian) - part 1 of Q answered

100% - yes areas served by different ring may overlap, assuming single phase supply.

as for part 2: your responses open a can of worms I fear:

first, in passing:

that's what I understood, but if they are labelled 'indoor use by computer/hifi/Tv only' & the sockets are a different colour (eg yellow/blue/red) is that enough to make them 'not likely to be used outside?

now you're ahead of me Orwain:

The current set up is the front of house (including kitchen & HW) is on a CU RCD: the rear (2 rooms & a workshop is on a fused CU (some rewireable, some cartridge). Both connect into a single master switch. (Don't ask why - reasons lost in the mists of time). Plan is put it all on a sound footing asap, hence this post.

I've lost (open) files several times by running the computer off the RCD circuit (eg Excel can corrupt files it has open if the switch is thrown). Since moving it onto the fused ring there's never been any trouble.

Both circuits test completely Ok for insulation & earth - neutral short. Nuisance tripping comes mainly when certain tools (all double insulated - so no earth) are run off the rear fused ring - only the tools keep going but the front CU is the one that trips. Observation suggests overload is the cause - an extra thick hedge twig or heavy pressure on the hand sander.

So what's happening? & will Christian's solution of an RCBO for each cct cure it?

Yes, It's not just the computer & the nuisance value of resetting clocks. Having an RCD in the workshop perturbs me - a nuisance trip could leave me in the dark with a powerful rotary saw still spinning. So why is an RCD needed/recommended/required in a workshop? As for distance from the supply source, most of the house is far further away than the remotest cranny in my workshop.

[Owain]

"northern_relayer" wrote Are you the OP formerly known as "the yorkshire dalesman"? | > That is because there is the possibility they may be used for | > outdoor equipment. Sockets which 'may' be used to power outdoor | > stuff MUST be RCD protected. | that's what I understood, but if they are labelled 'indoor use by | computer/hifi/Tv only' & the sockets are a different colour (eg | yellow/blue/red) is that enough to make them 'not likely to be used | outside?

I don't think it is. The colour of the socket is meaningless in terms of the regulations and a 13A socket should be suitable for supplying any equipment usually fitted with a 13A plug. This is why 13A sockets should not be fitted to 6A lighting circuits for table lamps and the like.

The spirit of the regs is clearly to ensure that equipment used outdoors is very likely to be plugged in to an RCD-protected outlet. If a dedicated RCD-protected outlet marked 'for external equipment' is provided in convenient places as required, that is likely to be used in preference to any other and thus the reg will be satisfied, AIUI.

| I've lost (open) files several times by running the computer off the | RCD circuit (eg Excel can corrupt files it has open if the switch is | thrown). Since moving it onto the fused ring there's never been any | trouble.

You might want to consider a small UPS for the PC, especially if you're in a rural area where overhead line failures are foreseeably more common.

| Both circuits test completely Ok for insulation & earth - neutral | short. Nuisance tripping comes mainly when certain tools (all double | insulated - so no earth) are run off the rear fused ring - only the | tools keep going but the front CU is the one that trips. Observation | suggests overload is the cause - an extra thick hedge twig or heavy | pressure on the hand sander.

Overload shouldn't trip an RCD because RCDs don't trip on overcurrent, only on a current imbalance caused by earth leakage. Anyway, you obviously have problems with your wiring and with rewireable fuses are well overdue for a rewire.

| So what's happening? & will Christian's solution of an RCBO for each | cct cure it?

RCBOs on each socket circuit ideal but a bit expensive. Split-load CU is usually an acceptable compromise, especially if workshops and the like are run from the non-RCD side and given their own local RCD protection.

You need an RCD on the workshop sockets for the same reasons as anywhere else, only increased: handheld power tools, risk of abraded or cut flex, wet hands, etc. Just don't have the lights on it.

Owain

[Martin Angove]

How about installing special sockets for the IT equipment so that you have to fit different mains plugs? It doesn't matter then if they're not RCD protected - it's a faff to set up, but you're not going to be able to plug your drill in. This is commonly done in offices with sockets which have differently shaped earth pins for example. I've used some really good (though expensive) "Electrak" sockets in the past for a similar application (making sure plebs didn't plug a kettle into a circuit supplied by generator).

The only thing to watch is that any plug for connection into a standard domestic circuit *must* be fused, so no using any of those nice European "Shuko" types :-)

Can't find the Electrak in CPC - I'm sure they used to do them! RS do do them, or did last time I had access to a catalogue, but I find their website a pain in the backside so I'm not going to look for them now :-)

Just an idea...

Hwyl!

M.

[Owain]

"Martin Angove" wrote | How about installing special sockets for the IT equipment so that | you have to fit different mains plugs? It doesn't matter then if | they're not RCD protected - it's a faff to set up, but you're not | going to be able to plug your drill in. This is commonly done in | offices with sockets which have differently shaped earth pins for | example. I've used some really good (though expensive) "Electrak" | sockets in the past for a similar application (making sure plebs | didn't plug a kettle into a circuit supplied by generator).

That's one application for non-standard sockets, another related one is for IT equipment with high earth leakage.

I really don't know whether that would actually be acceptable for a house; you could still have the situation of a lead plugged in and live, and the little holes on the free end of an IEC lead are so inviting to 3-year-olds and paperclips :-)

The OP's argument is not with RCDs per se but with nuisance tripping. That should be avoidable with proper discrimination between protected circuits.

| The only thing to watch is that any plug for connection into a standard | domestic circuit *must* be fused, so no using any of those nice European | "Shuko" types :-)

But it wouldn't be a "standard domestic circuit" (and anyway 5A plugs on lighting circuits aren't fused) - all that is required is to ensure the circuit is fused at an appropriate level for the flexes. An alternative would be to use fused sockets.

| Can't find the Electrak in CPC - I'm sure they used to do them! RS do do | them, or did last time I had access to a catalogue, but I find their | website a pain in the backside so I'm not going to look for them now :-)

do power strips with individual socket fuses if wanted and a variety of non-standard plugs (Elektrak, MK, Wandsworth, etc).

Owain

[RichardS]

I think that the easiest way to satisfy this requirement is to install some weatherproof IPx6 sockets outside in areas that you would be normally using the outdoor equipment - ie strategic places around the house.

Make sure this circuit is adequately RCD protected, and isolate the sockets from switches inside if necessay (if you're worried about people nicking your leccy!).

If there are sockets in sufficient positions for all round house access then this would make it most unlikely that an internal socket was used for external appliances, therefore to my reading of the regs you would not have to protect the internal sockets.

I'm sure others will comment upon whehter this would be sufficient.

It's also very convenient, and means that you can do dusty/messy jobs outside will all the doors/windows securely closed so you don't get dust/grass clippings/etc migrating into the house...

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[Christian McArdle]

On the other hand, I wouldn't dream of not protecting the inside sockets. I think the regs should be changed to mandate the protection of inside sockets, except in special circumstances (i.e. non domestic situations). However, I agree that waterproof outside sockets should be provided with independent RCD protection, as well.

Christian.

[the yorkshire dalesman]

many thanks for all replies - I see there is a parallel posting running

Re: OT - Fitting RCD in household mains supply

which goes into these issues in some depth.

Whilst I appreciate the benefits of appropriate fitting of RCDs, I'm unconvinced that they are always appropriate. Safety is something that has to be managed & you have to weigh up the pros and cons of the different options.

Agreed, my elec installation is overdue for update - but that's how this post started & renewal work is in slow progress. Nevertheless what happens poses some curious Qs. eg:

1. The front of house RCD (30mA) CU CAN trip when a light bulb blows or it can be the MCB in the lighting cct: both happen, though perhaps the MCB trip is the more common.
2. The Hedgecutter fed off the rear fused cct (with or without an in-line RCD socket) usually makes the front RCD trip - while the in-line RCD stays on. ditto for the B&D sander & other m/c tools (but less often). All these are double insulated with 2 wire cables - so where is the earth leakage?

Some time ago I queried all this with an elec engineer who made the helpful(?) observation that 'loops sometimes do funny things'

I'm far from convinced that there's a fault of the simple shorting/leakage type. Seems to me more likely that the tripping is due to

a) the L-N imbalance detected by the RCD must be something to do with variations in power factor & not earth leakage - ie capacitances &, perhaps, inductances in the motors & suppressors:

(b) the peculiar design of elec hand motor tools - which are not straight forward inductance or synchronous motors - more some bastard style of ac commutator motor (I've only a very rough idea on these things). Still leaves the mystery of why fusing light bulbs trip the RCD (but answer may be in the parallel post).

Lastly I'm still slightly paranoid about maintaining supply the the electronics around the house especially this computer which is on most of te time, even if I'm out. The fitting a UPS would be 1 answer but that is expensive & would still leave sockets (on the UPS) which are effectively unprotected.

[Christian McArdle]

There could be a neutral to neutral leak between the front and rear consumer unit based circuits. This way, some of the neutral current could go through the wrong RCD. The front RCD is then more sensitive and always blows first. Just a thought.

Christian.