Extending a ring mains

molerat

But if you have not fiddled the sums to get the correct answer and paid the tax it is unsafe.

Owain_Moneysaver

The minimum cable sizes for a ring final circuit is 2.5mm live and neutral and 1.5mm earth, unless Mineral Insulated cable is used when 1.5mm l&n is permitted.

1.5mm cable is typically suitable for fused spurs i.e. 13A or less, or 10A lighting circuits.

The actual current carrying capacity of any cable depends on its installation method (surface clipped, buried, next to insulation, etc), whether it is grouped with other cables, and whether it is protected by a MCB or a rewireable fuse.

The minimum current carrying capacity of a cable on the ring circuit must be 20 amps, because although there are two cables in parallel on the 32A MCB, you cannot assume that the current will flow equally in both halves of the ring. Rings should be designed to avoid a drastic imbalance, but some imbalance must be allowed for.

joeblags

In the past I had an electrician connect live to neutral in a switch




lol.... that's because its a switch live and there is no neutral, the blue/black should of been sleeved with brown sleeving. an electrical wont just sign off your work either


infact after reading how little you know I wouldn't even sign you off for wiring a 13a plug onto flex cable.

rich13348

I don't think OP meant they joined brown to blue with brown sleeve. Considering they said it was loud and a bright flash.

NICHOLAS_2

What is is you are trying to do, add an extra socket?

You could run a single cable from an existing socket to your new location. You wouldn't need 50 meters of cable then? Just pointing it out.

NICHOLAS_2

I think we get 100m from our supplier for 48 pounds cash price, no VAT.

So, £30 is probably not far off what we would pay him for 50m but he also sells us by the meter which is why i say if you are not running long distances you may be able to get it cheaper.

Horlock

Thanks everyone for the constructive feedback. I've ordered 2x2.5 +1.5. I ordered 50m. I know this sounds quite a bit and I'm suspect I'll have wastage, but wont be too much wastage. Initially, I'm only adding one room, it measures about 5m x 3m, so just to get around (excluding the ups and downs from the floorboards and the wastage from first fit) it'll be 16m. I'll put 4 double sockets in the room, so guessing I'll need at least 4m for that. Then when all finished, I'll be moving on to the garage, which will probably want another 4 or 5 sockets (although this will be done from its own consumer unit). I'll be doing two outdoor sockets, which I'll keep separate to the garage ring. I also want a 32amp socket in the garage for welding - so nearer the time there might be questions on this too (currently guessing that'll be a 6mm cable - but that is so far off I've not done any research yet).

Anyway. Thank you everyone. Always nice to have helpful answers with a minimum of trolling.

DevCoder

Have you got a copy of the OSG? If not Id suggest you obtain one.

Do you know what your volt drop will be on your new extended ring main? Depending on various factors the maximum floor area will be between 74 and 102 m2 on the ring circuit to comply.

Have you considered running a radial circuit from the CU to the new extension?

Do you know what your earth impedance will be?


You say you will be getting your electrician to test and cert the circuit extension, I assume you'll be leaving your install exposed so he can check it before you do any make good?

When it comes to the welding circuit, let a pro do it, thats a specialist circuit that you don't want to screw up.

rich13348

While we are on the subject I was looking at my CU and the main switch is rated 100A but the total potential load over all circuits is 172A. Its unlikely that I will reach that but let's say for instance I had my oven on full whack extractor fan on wife taking a rediculously hot shower as well as boiling the kettle and toasting all my crumpets in the toaster with eggs in the micro and TV and radio on full blast not to mention all the lights on.

Could this potentially trip the main switch without tripping each individual MCB?

Ben84

You should be fine. Your 100A supply can go up to 24 kW, which is a lot of electricity for a normal house.

As for consumer units/fuse boxes, I don't know about the latest ones, but the ones I'm familiar with the main switches are just switches. Heavy duty switches, but plain old switches none the less, so they don't trip when overloaded. What would blow if you went much above 24 kW is the 100A fuse on the supply wire (assuming you have a 100A service, some are 60A and things), which is typically a black box with a lead seal, which is fitted between the fuse box and the supply cable coming in to the house. I've never heard about anyone blowing one of these, but I suppose it could have happened to someone somewhere.