Electricity in porch

arciere

I am in the process of (among other things) wiring a small room we've got downstairs (we are on the first floor).

The easiest path the builder has found to the existing mains wiring is from a socket near the stairs. We will have around 8 sockets in the room downstairs (4 doubles), mainly used for low-powered devices plus a 2kW heater.

As far as I understand, the socket that the builder has used is part of a ring circuit. On the electric panel, it's connected to a 32A MCB.

Originally, he said that we could only get one or two sockets off a ring main but upon checking with an electrician, he was told that we can actually have more than one provided that we don't cover an area bigger than 50sqm (we don't).

Now, since I like to do my research, I think that this approach would probably be more reasonable:

- You can only have one spur per socket on a ring circuit, not unlimited;
- In my case, we could still get those 4 doubles off mains but we would have to use a 13A fused switch to restrict the downstairs usage to 13 amps max

Am I talking rubbish?

Jasonn1

I'm not an electrician but I think the number of the sockets isn't so important but rather the amount electricity you're going to draw from all of the sockets combined that are connected to that 32A MCB, so you need to calculate how many kw in total would be going through that MCB. If it's around 5kw-6kw then it should be fine, if it's around 8kw then it might be a good idea to change the MCB to 40A.

Carrot007

Jasonn1 said:

I'm not an electrician

...

if it's around 8kw then it might be a good idea to change the MCB to 40A.

I see why you suggested that.

However it seem's that the "electrician" for OP is suggesting radials off the ring main rather than extending it which would be a much better idea.

Of course others may dissagree.

arciere

Carrot007 said:

Jasonn1 said:

I'm not an electrician

...

if it's around 8kw then it might be a good idea to change the MCB to 40A.

I see why you suggested that.

However it seem's that the "electrician" for OP is suggesting radials off the ring main rather than extending it which would be a much better idea.

Of course others may dissagree.

Yes, that would be a radial off the ring main.

Which is fine by me (anything would be as I'm not an electrician), but having read here and there, you can't actually do that, unless you restrict the spur connection to 13A to avoid overloading the wires at any point.

arciere

Jasonn1 said:

I'm not an electrician but I think the number of the sockets isn't so important but rather the amount electricity you're going to draw from all of the sockets combined that are connected to that 32A MCB, so you need to calculate how many kw in total would be going through that MCB. If it's around 5kw-6kw then it should be fine, if it's around 8kw then it might be a good idea to change the MCB to 40A.

Yeah, but as far as I understand you need to take into account what the wires can handle. A 40A MCB doesn't protect you from overheating if you are using the standard 2.5mm wires, which is what I believe we have.

Ectophile

Don't stick a 40A MCB on it.  The standard UK ring main is pushing it a bit to use 2.5mm cables on a 32A breaker.  Each cable is only rated for about 18 to 21A, and relies on the two sides of the ring sharing the current.  There's no guarantee the two sides of the ring will be sharing the load equally.

If you create a 13A fused spur, you can put as many sockets as you like on that.  But you will be limited to 3kW of loads or risk blowing the fuse.

An alternative is to break the ring at the socket, and then make a new loop round all your new sockets, connecting it to the two broken ends of the original ring.  So long as the new ring you've created isn't too long, that's OK.  Any competent electrician will be able to calculate and/or test whether the extended ring is good.

arciere

Thanks Ectophile, really nice explanation.

I'm more than happy to have a 13A fused spur, apart from the 2kW heater (which will be running at half of that most of the time), I'm not planning on using anything high-powered in the room (only a tv and a couple of table lights). If we do need to use say a vacuum cleaner, we will make sure that the heater is off.

If it trips, we'll replace the fuse and will remember next time, but still 100 times better than risking a fire.

fenwick458

so just to clear things up:
The OP could fit as many sockets as they like in the new room (lets make up an arbitrary number like 10 extra double sockets) and theoretically thats fine provided they are all on the ring main , and the total surface area of the floor space served by that ring main isn't increased to more than 50m^2
if extending the ring main isn't possible(for some reason) you'd have to have a fused spur on the ring main, and a radial circuit coming from that fused spur which would be limited to 13A,  but then again from there lets assume you want 10 sockets then yes thats fine as long as the total current draw (from the extra 10 sockets) is below 13A
I think the most important thing to take from this is (and it seems obvious really) is listen to what the electrician says rather than listening to the builder

Jasonn1 said:

I'm not an electrician but ......

any information after that statement just take with a pinch of salt. DON'T upgrade the MCB to 40A

arciere

fenwick458 said:

Jasonn1 said:

I'm not an electrician but ......

any information after that statement just take with a pinch of salt. DON'T upgrade the MCB to 40A

Thanks, I know enough to understand that circuit breakers are there to prevent damage to the wires, not the other way around.

MalMonroe

You said " fine by me (anything would be as I'm not an electrician)".

In that case, you are extremely foolhardy. And I'm really surprised that people here are actually attempting to advise you what to do. Don't forget that it's not their house or family that will suffer if things go pear-shaped. I'd like to take a bet that they're all men, too.

My suggestion would be that you need to consult a fully qualified and experienced electrician immediately if not before and NOT do this work yourself. Because although you are willing to carry out electrical work, sadly you are not an electrician.

You say "If it trips, we'll replace the fuse and will remember next time, but still 100 times better than risking a fire." But what about risking a life if you've done it all wrong?! What if there is no 'next time'??

No amount of money saved will compensate for any life lost by not doing things properly. This is just crazy and I've a mind to report this whole thread because quite frankly it's ludicrously dangerous.

arciere

Jeez, where did you actually read that I was doing the job myself?

I was merely asking a broad question to see what to expect and what people with more experience than me would do.

Do you really think that I would do electrical work myself because of what someone suggested on a random forum online?

Chill man, 2022 has barely started...