Extending a ring into extension 1

[shabbaranks]

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Using a dual box provides an extra socket and removes the need to have cables jointed in terminal blocks behind a socket,

Thanks for this - like you say a much neater approach to getting the job done

 

[shabbaranks]

Step one is look at the original installation certificate or measure R1 + R2 or at least the prospective short circuit current or loop impedance and work out if extra cable can be added to the ring final. 106 meters is considered to be maximum length to comply with volt drop, but also depends on the over current device, for example a B32 MCB will trip on the magnetic part of the trip with 5 times rated valve, so 160 amp, using ohms law, this equals approx 1.44Ω and add 5% for safety, 1.36Ω so step one is be enquiry (reading installation certificate) or by testing, (using the loop impedance meter or low ohm meter) work out if you can add to the ring final.

Using a twin back box and two single sockets, or a double back box and two grid sockets, is likely the easiest way to split the ring. To add to the circuit the circuit will need to be RCD protected, and I think the new edition is now in force, so will need to be a type A, can't use type AC any more.

But before jumping in first is to ensure the LABC will let you do it. When I came to do the electrics in my mothers wet room, I had a problem getting the LABC inspector to allow me to do it, he did in the end, but it seems there is a tick box on the building application and when you make the application you need to select if using a scheme member or not to do the electrics, my LABC wanted me to pay for some one to come in and test the installation which I would need to pay for, the cost of the inspection would be more than the cost of using a scheme member electrician.

So you need to have the calibrated test set to show the LABC inspector, and some proof you know what you are doing, like a city & guilds 2391 certificate.

When Part P came out it was one fee, which in Wales was £100 plus vat for first £2000 worth of work, and the LABC inspector had to either test and inspect himself, or the LABC paid for the third party inspector, but that changed, and now the LABC can charge you with cost of inspector, so it can get rather expensive if your not doing your own inspecting and testing.

It is the same for a lot of the building work, windows for example need a certificate or you pay the LABC, so in real terms near impossible to build an extension without the LABC being involved, and the last thing you want, is for it to be nearly complete, but the LABC will not issue the completion certificate without some other paperwork, like the compliance certificate issued by the scheme members electricians scheme.

So do check with your LABC inspector what he will let you do, we found Liverpool very helpful, and no real problems, but Flintshire were really strict, so a lot depends where you live.

Hi
Thanks for your reply - I will get the whole extension checked by a qualified electrician and signed off properly so its not a problem. Just with everything being so expensive at the min its handy to be able to do a few bits yourself to keep the costs down (like chasing walls and running cables). We seem to have struck it lucky with the BC - a really friendly person and also willing to help\offer advice (and obviously conform to the regulations) but like everything there are ways and means on how they go about it.

 

[SUNRAY]

Hi Mate

As far as I know I only posted it once - but thanks for the comment (did you get out the wrong side of the bed?)

I like others appreciate forums like this where people share their knowledge - Im sure in life we all have something to contribute. I dont expect people to jump on and answer me straight away (or at all) but for those that do its really helpful.

It's not a problem and likely happened when you added the second image.

 

[Taylortwocities]

As far as I know I only posted it once - but thanks for the comment (did you get out the wrong side of the bed?)

I made the comment to help you. I was in no way accusing you of anything.
If a topic is duplicated, for some reason, then you can have the situation where half of the replies are on one thread, and other replies appear on the second thread. This can cause confusion (especially for you) as one lot of replies will not have seen the second set of replies. So you could get duplication or (worse) conflicting advice.

Luckily there is a way to bring the two together. And this has happened.

Hopefully you now have the answers you need? I can't add anything further.

 

[ericmark]

Hi
Thanks for your reply - I will get the whole extension checked by a qualified electrician and signed off properly so its not a problem. Just with everything being so expensive at the min its handy to be able to do a few bits yourself to keep the costs down (like chasing walls and running cables). We seem to have struck it lucky with the BC - a really friendly person and also willing to help\offer advice (and obviously conform to the regulations) but like everything there are ways and means on how they go about it.

In the main having an EICR done after will highlight errors, but really you want to highlight errors before not after.
This web page goes through the procedure to test the ring final what you need before starting is to measure.
Step 3. Measure between Line to Line to get the reading for “r1”
Step 5. Measure between Earth and Earth to get the reading for “r2”
However these readings need adding to the incoming loop impedance reading, and without that your stumped. So unless you have an installation certificate giving the readings, you can't work out if you can add to the ring final.

For the inspector he knows what the maximum allowed loop impedance or prospective short circuit current is, so he simply plugs in and tests, if it passes OK, if it fails then do it again and do it properly. But that is not really what you want, what you want to know is, when I add 20 meter to the ring final will it pass before you add 20 meters.

Limit for the ring is 106 meters, so when re-wiring a house, simple, use one role of cable, if one is not enough then form another circuit. But how can you measure how much cable is already used? The easy answer is guess where the centre of the ring will be approx, and measure the sockets around that point.

You will need to fill in these forms this

one is what you are interested in, you should already have one from when the house was first wired, this

and this

tell you what the readings where when built, also found on an EICR, and from that you can work out if you can add to the circuit, other wise it needs measuring first.

I am sure many even electricians have tested and realised they have over stepped the mark, and with RCD protection and modern switch mode power supplies you can fudge up some results and get away with it, but with an independent tester coming after it has all been done, no option to fudge results, and the do it again and do it properly is not what you want.

If BC were not involved likely you could fudge results, but they are.