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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Radial circuit with joined ring main and CU questi https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1523565687 Message started by Natedog on Apr 12^th, 2018, 9:41pm

Title: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 12^th, 2018, 9:41pm

I've had some upstairs floorboards up this week trying to stop them squeaking, and I've come across an interesting bit of wiring which I think needs looking at, just after your opinion please

Theres a round junction box that's got 4x 2.5 t&e going into it. 2 of them are grey covered, as with all the wiring in the main house, and the other 2 are white covered like all the wiring in the "new" extension (mid 90s, built by OH's ex husband)

We had the kitchen redone a few years back. There was only 2 sockets originally - one over the worktop and one behind the fridge, both on the downstairs radial circuit. These were left alone, and a new ring main was added for more sockets, dishwasher, extractor etc. At the same time the old 4 fuse CU was removed and replaced with a 12 way split load one. All 12 ways are being used. At the time, we thought that the new sockets in the extension had been done by just extending the radial circuits upstairs and downstairs.

Looking at this wiring I've found, one grey one heads towards the CU, one goes to a socket in the bedroom and the 2 white cables head off towards the extension. I'm thinking now that it might be that its a ring main that has been grafted onto the radial circuit as a temporary measure until the consumer unit was upgraded, which he never got round to doing.

If this is the case, I'm assuming that the best thing to do would be to remove them from the junction box and put them on a circuit of their own? There is a fair bit of a lack in the cables, so I think they will probably reach the meter cupboard without being extended. But having shelled out for a new CU to be fitted relatively recently, ideally I don't want to have to scrap that and swap it for a bigger one. The only thought I've had on this would be to put 2 of the smaller radial circuits (there's a couple with just 2 or 3 sockets on) back to being fed from one breaker as they were before, freeing up a breaker for the extension's ring main.

Alternatively, is it possible to fit a 2nd smaller consumer unit just for that 1 circuit, which would leave space for adding additional circuits in the future, such as power and lights for the garage.

Thanks in advance :-) and sorry if that's a bit of a waffle

Title: Re: Radial circuit with joined ring main and CU questi
Post by Lectrician on Apr 14^th, 2018, 7:28am

You would want to disconnect the two whites, reconnect the greys. See what no longer works. Test the whites end to end to see if it is a ring. Only once you have confirmed your initial thoughts can you then decide what to do. If no spare ways, you would need to create one by doubling circuits. As it stands, it’s non standard, but not dangerous. What rating are the radials?

Title: Re: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 14^th, 2018, 8:09pm

There's 2 short radial circuits with only a couple of sockets on, both are on 16A breakers

There's 2 larger radial circuits on 32A breakers

And the new kitchen ring main on a 32A

It's one of the larger radial circuits that the odd bit is on.

Title: Re: Radial circuit with joined ring main and CU questi
Post by Lectrician on Apr 15^th, 2018, 8:00am

Is it a 4mm² radial?

Title: Re: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 15^th, 2018, 10:18am

It all looks like 2.5 the only cable that looks bigger is the cooker

Title: Re: Radial circuit with joined ring main and CU questi
Post by Lectrician on Apr 15^th, 2018, 6:55pm

You shouldn’t have a 32amp radial on 2.5mm²

Title: Re: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 15^th, 2018, 8:48pm

I did wonder.

What's a sensible number of sockets to have on a 32A ring that doesn't include the kitchen? Another thought I had was to replace that 1 junction box with 2, so the ring that has been added to the radial circuit just becomes part of the radial, then find the last socket and add a return back to the consumer unit to make it a ring

Title: Re: Radial circuit with joined ring main and CU questi
Post by Lectrician on Apr 16^th, 2018, 6:28am

That would be an option.

A ring circuit can have an unlimited² number of sockets, but cannot serve a floor area larger than 100m². The cable length should not exceed around 100m also, otherwise you may exceed volt drop and Zs.

In a typical house, one ring for the kitchen and one for rest of the house would be a minimum really. There is nothing wrong with multiple radials though.

32 amp ring, 2.5mm² cable, 100m² floor area
32 amp radial, 4mm² cable, 75m² floor area
20 amp radial, 2.5mm² cable, 50m² floor area

Title: Re: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 17^th, 2018, 12:25pm

Thanks for your advice :)

I will work out exactly what is on each circuit for starters. Hopefully having some plastering done in a few weeks, so would be the ideal time to sort it, while the carpets are up anyway

Title: Re: Radial circuit with joined ring main and CU questi
Post by londonman on Apr 17^th, 2018, 10:27pm

Natedog wrote on Apr 17^th, 2018, 12:25pm:

You're plastering your floors ? ;D

Title: Re: Radial circuit with joined ring main and CU questi
Post by Natedog on Apr 20^th, 2018, 11:26pm

If I can't find a plasterer who can fit me in and end up doing it myself, then probably yes ;D