Period Electrics (regs)

[Flyfisher]

. . . or more accurately, modern electrical regs in period houses.

Like many period properties we have rooms with just one doulbe socket and even some without any at all. In some of these rooms the double socket has been spurred off a ring main, which I understand is perfectly ok (unless I'm out of date with the latest regulations).

I would like to add some more sockets to various rooms but my understanding is that only a single spur is allowed off a 30A ring main, which makes sense.

My question is whether it is acceptable to replace the 30A MCB for the ring main with 20A (or even 16A) and then add more than one spur, effectively creating a radial circuit? Thus, the 20/16A MCB would correctly protect both the 2.5mm2 radial cabling and the existing 2.5mm2 ring cabling. I'm confident such a thing is electrically ok in terms of cable ratings and fuse protection but I'm less sure about the more 'esoteric' regulations such as diversity in 'living' rooms (ie not a kitchen) and sockets-per-floor-area guidelines etc.

I appreciate that the total power capability of the circuit will be dramatically reduced but for the typical modern mix of TV, hi-fi system, chargers for phones/tablets/laptops and table or standard lamps even 16A will be perfectly fine. And in the unlikely event that someone plugs in two 3kW fan heaters then the MCB will trip to protect everything from overloading (just as a 30A MCB would trip if someone plugged three such fan heaters into the same ring main).

 

[fernicarry]

Like you say from an electrical pov perfectly safe to down-rate the circuit to match your proposed cabling. I don't think you will fall foul of any regs per se. My understanding of the regs is that they are qualitative not prescriptive, so long as its safe, the workmanship is good etc. Might be pointed out in an inspection that its a deviation from 'standard' practice but it would have to be one heck of an inspection to figure out where the cables are buried! Biggest issue will be making sure that someone in the future doesn't 'fix' it by swapping a 32A breaker back in.

I don't think diversity has anything to say about the circuit configuration, its more about calculating the likely total demand. With a ring the potential issue is if the ring is unevenly loaded i.e. all the heavy loads are on one side close to the board so being supplied predominately by one side of the ring which could then find itself being overloaded. You could potentially make that worse with your radial but a 20A breaker is sufficient to protect a single run of 2.5mm in most circumstances.

I removed many, many spurs from our ring circuits and more than a couple had multiple sockets on them, all of them on bog standard 32A breakers, and the house hardly ever burned down. One mini-radial upstairs was actually spurred off the old kitchen ring directly at the fuse-box, so was hardly an accident. The immersion heater was spurred off the downstairs ring, again at the board, we didn't know this until it developed a fault and took out all of the downstairs sockets. My wife had to run the TV off a very long extension lead for a few weeks until I got home. Both sockets in the back bedroom were spurred off the kitchen below, also didn't realise until the day before the new kitchen ceiling was due to go up necessitating a very swift rewire.

My new upstairs ring is also down-rated to 20A, not so much because of cable size, but to keep the total load for the whole board (after diversity) under 100A. It can be a bit trippy when first powered up because there are a few computers and other tech things up there. The inrush on their power supplies can be enough to knock off an MCB. Flicking the toggle again immediately afterwards gets it going.

If this was a serious problem you could go up to a C-curve breaker but you'd have to do your diadic (sp?) calcs -- essentially can the cable withstand the short term overload it will experience whilst the breaker gets its act together without permanent damage. C-curve breakers not usually found in domestic properties so again might raise eyebrows but perfectly acceptable, if done properly.

Disclaimer -- I'm not a qualified sparky.

 

[Flyfisher]

Might be pointed out in an inspection that its a deviation from 'standard' practice . . .

Yes, that's the sort of intangible thing I was a bit concerned about. The sort of thing that a 'jobsworth' inspector might not be happy to sign off.

I think I'll go ahead anyway and be prepared to argue my case - it would surely be an odd situation to be castigated for installing a lower rated MCB than 'standard practice'

 

[fernicarry]

I think in England you are allowed to add to an existing circuit without it being notifiable, the Part P rules. The rules in Scotland are a bit more relaxed, at least for a property of our type where I can do anything at all without getting building control involved. Which is good because I had 3 different electricians blow me off when I was trying to get the rewire kicked off and ended up just figuring it all out for myself.

 

[Flyfisher]

I've lost track of what DIY electrics are allowed these days, though I guess it's all online somewhere.

Having a stock of red/black cable can sometimes help. Obviously I'd never use it but who knows what a previous owner might have done? :wink:

 

[Owain]

You may be better, if possible, to find the 'far' end of your ring and split the ring there, then move the ends at the consumer unit on to two separate 20A MCBs, That way you have two radial circuits x 20A, rather than one. Even better if they can go on separate RCDs or RCBOs.

You can also have unlimited sockets downstream of a fused spur if you need a lot of sockets for low-powered items somewhere.

 

[Flyfisher]

Good suggestions, but as you say it's down to 'if possible'. In my case the ring is upstairs and the existing spur is in a downstairs room. I want to add more downstairs sockets but only have the single spur to work with.

As with most domestic wiring, the actual circuitry is straightforward but it's the cable routing that defines the difficulty of the job and, like most period property owners, I'm trying to minimise the disruption to walls and floorboards.

If I had easy access to every bit of cabling then I'd merge the existing spur and the proposed additional sockets into the existing ring - a simple wiring job but unfortunately one that would involve chasing an additional cable into the wall to take the new downstairs ring cable back upstairs. I'm trying to avoid that.

As for a fused spur and unlimited sockets, that's pretty much what I have in my study for the PC, screens, printer, scanner, speakers, phone, etc, . . . all plugged into a single wall socket using two 6-way socket strips.

 

[Zebra]

When you say " only a single spur is allowed off a 30A ring main" what you mean, if I understand correctly, is that only one socket or outlet is allowed to be spurred from any one point on a ring. You can have as many spurs as you like off a ring, but each must have only one double socket, unless, as Owain says, you insert a fused connection unit. Then you can put what you like downstream of it.

If it were me I would be happy, under the circumstances, with downrating the ring to 20A in order to treat it like a radial. The main issue, as Fernicarry says, is that someone might change it back in the future. I agree with Owain that a preferable option if you have the spare ways inside your consumer unit would be to actually make it into two 20A radials by finding the midpoint and disconnecting one of the legs. Preferably take it right out of the box, and disconnect that piece at both of the sockets which it is connected to.

It's not true though, Fernicarry, that in England you are allowed to add to an existing circuit without it being notifiable under Part P. Adding a new circuit is notifiable, but such alterations as Flyfisher is talking about - adding extra sockets - is not notifiable unless they are in a kitchen or "special location" ie bathroom (yes, you can have sockets in a bathroom now as long as they are more than 3m from the edge of the bath or shower....).

Gosh, I haven't done any sparkying work for 18 months now and I'm getting rusty on this stuff!

 

[Flyfisher]

When you say " only a single spur is allowed off a 30A ring main" what you mean, if I understand correctly, is that only one socket or outlet is allowed to be spurred from any one point on a ring. You can have as many spurs as you like off a ring, but each must have only one double socket

Good point - yes, I meant only one spur from any point on a ring. Typically from one of the ring sockets. I wasn't sure about it being non-notifable though, so thanks for that clarification.

As for such downrating to 20A having the risk that someone may revert to 30A in future, well yes, but such risks are practically impossible to avoid. What about someone replacing a 6A MCB with, say, a 16A one? I understand that ANY work to a consumer unit is notifiable so such risks are sort of covered by the regs, but of course they can't physically prevent such things.

Perhaps there will come a day where CUs are sealed units, like gas/electricity meters?

 

[Zebra]

I understand that ANY work to a consumer unit is notifiable

No I don't think so. Adding a new circuit is, so perhaps there's a grey area in terms of whether you are effectively creating a new circuit, but you can change a breaker without it being notifiable, and I you can move circuits around inside the CU.
I think the risk of someone upgrading a 6a circuit to a 16a is not quite comparable, because presumably said circuit would be wired in 1.5sqmm cable so that wouldn't look like an option. One could quite legitimately upgrade it to 10a depending on the circuit length, earth fault loop impedance and achieving trip times, but not 16a.
The specific risk in your situation is that someone looks inside the cu, sees it's wired in 2.5sqmm, tests end-to-end continuity, and thinks "well knock me down with a feather if that's not a ring, I'll jolly well change it to a 32a" without knowing about all the spurs.
Now, that doesn't mean you can't do it. There's nothing in the regs about making sure someone doesn't come along in future and have a different view on things. If what you do complies, well there you are. You could leave a circuit diagram with the consumer unit. You could write in permanent marker "20a only" on the cable sheaths where they enter the consumer unit, and you'd have done what you can.
Someone could always come along and do something different. Someone could come along and swap all your MCBs for jelly babies. It wouldn't be notifiable, but it would be a silly thing to do.
It's still better to split it up into two radials, but creative solutions and workarounds are common, like in anything else. In my opinion! Of course, different electricians have different approaches.

 

[Abi Cott]

Trust me. Idiots regularly upgrade the mcb because it keeps tripping.

I've lost count of the number of times a customer has asked for help with finding a 45amp mcb because they've had a new shower fitted and the 30amp one keeps tripping.

My general reply is that they can burn their house down if they wish but I'm not going to help. I've had reactions that varied from surprised to confused to downright offended.

 

[Flyfisher]

Trust me. Idiots regularly upgrade the mcb because it keeps tripping.

I've no doubt . . . Just as they wrap silver foil around plug fuses (or use a suitable sized bolt!) or use multiple bits of fuse wire in old style porcelain consumer unit fuses

 

[Flyfisher]

The specific risk in your situation is that someone looks inside the cu, sees it's wired in 2.5sqmm, tests end-to-end continuity, and thinks "well knock me down with a feather if that's not a ring, I'll jolly well change it to a 32a" without knowing about all the spurs.

Yes, that's a possible scenario, but one I'd say that supports any changes to a CU being notifiable to ensure a 'competent person' does the work (assuming people follow the rules in the first place!)

I'd also say it's a scenario that could be more easily avoided if there was more documentation associated with electrical installations. As we all know, domestic houses come with pretty much zero documentation, so even when a competent person is asked to do some work, how will they confirm the state of the wiring? What would you do if asked to swap a 20A MCB for a 30A one? Presumably you'd have to open up every socket in the circuit to determine precisely how it was wired?

Another scenario could be that I sell the house to someone who decides to swap out the 20A MCB for a 30A one, but being the responsible sort, then notifies building control and asks them to do a full test of the complete installation. The end result would then be an installation with up to date certification . . . . but what are the chances that the multiple spurs off a single ring socket would actually be noticed?

I'm not arguing against the principle of part p regulations, but there do seem to be many loopholes and areas of confusion. In contrast the Gas Safe regulations are far easier to understand - if you're not certified then it's illegal to do any gas work at all (as I understand things). I wonder why the powers that be decided to treat electrickery differently?

 

[Zebra]

Well yes, maybe alterations in a consumer unit should be notifiable. I thought the question was whether they are, not whether they should be.

And yes, ideally there would be more documentation associated with electrical installations. But absent that, if asked to swap a 20A MCB for a 32A one yes I would feel obliged to check there weren't spurs. There's a method though, the R1+R2 test, which if done properly, checks for exactly that.

So in your scenario where a future owner swaps out the 20A MCB for a 32A one then gets it tested, that should be picked up, if the electrician doing the testing is thorough, which of course they might not be.

And yes Part P is a little weird but presumably the lines were drawn where they are in order that householders aren't totally forbidden from doing anything at all, but hopefully can't make too much of a mess of things!

 

[Flyfisher]

And yes, ideally there would be more documentation associated with electrical installations. But absent that, if asked to swap a 20A MCB for a 32A one yes I would feel obliged to check there weren't spurs. There's a method though, the R1+R2 test, which if done properly, checks for exactly that.

So in your scenario where a future owner swaps out the 20A MCB for a 32A one then gets it tested, that should be picked up, if the electrician doing the testing is thorough, which of course they might not be.

That's reassuring and, as you say, a 20A MCB with 2 x 2.5mm2 cables at the CU would be a clue that something is not quite 'standard' and should merit a bit more careful attention during testing.