Splitting ring main

[whazza22]

Hi all,

I have a cpc continuity fault on a ring main which only consists of 7 sockets and 2 FCU.

I have split the circuit and found that it is one of the legs coming from the C.U to the first socket.

Normally I would convert to 2 radials but this is not possible and also its concrete floor. The client does not want me to chase the wall and replace the leg.

Is it possible to convert to one radial on a 20a mcb?

The main appliances used would be kettle, microwave, boiler, fridge, freezer and tv.

Thanks

 

[rattlehead85]

May i ask why this is not possible to split as you said.

 

[Deleted member 9648]

May i ask why this is not possible to split as you said.

Because it's the first leg from the CU to the first socket...which means he can only have one radial.

Yes it is possible to convert to one 20a radial....load allowing.

 

[rattlehead85]

Can you not put the unaffected portion onto a 20a like you said, lose the damaged point and blank off. It could just be you have either a loose or open connection at board/ socket or even a fragmented c.p.c core within the sleeving inside the board (if it is T&E that is)

 

[whazza22]

As wirepuller said. It's not possible as its the first leg.

Would have to work out the max demand!

 

[rattlehead85]

Oh right i see so if you split at damaged point power up one leg you get all sockets live with correct earth, other leg you get nothing live with no earth. 20a should be o.k as wirepuller says. Only doubt is it is a kitchen load with some reasonably heavy draw.

 

[whazza22]

Yeah kitchen is possible the only problem.

The appliances plugged in are kettle, microwave, fridge and freezer. Plus spur for boiler and cooker hood.

 

[telectrix]

convert to radial on a 20A MCB, as you suggest. if the customer has problems with the MCB tripping, then it's his own bloody fault for refusing to have the RFC reinstated.

 

[markc123]

Abit of a bummer when the customer doesn't want anything ripped up.

Like been said, convert the ring into a radial - so effectivley the first socket becomes the last and down grade to 20a. You'll then just have to advise the client about the possible overload issues if everything is on at once. Not much you can really do when the client doesn't want anything physically disturbed.

 

[Octopus]

If its a short "ring" what is the highest R1 + R2 reading and what are the actual Zs tests like?

 

[whazza22]

The Zs was averaging 1.09 but one socket was 1.40 which is too high but that may be because of the earth fault.

 

[rattlehead85]

TBH you have L-L & N-N continuity so you have no issues with cables not being protected against overload by the MCB. The c.p.c is broken which is sending the Zs values above the permitted tolerance of the MCB, however as the circuit should be RCD protected to 30mA this eliminates the problem with disconnection times and fault clearance which would exist if no R.C.D was connected. Therefore i cannot see any immediate issues.
I stand corrected if somebody can highlight any condition i haven't taken into account. The R.C.D is the important factor here.
Although this warrants a C2 on an EICR if the client refuses correct remedial action to make this circuit comply as a ring the best thing you can do is detail the condition, reasons why it has not been rectified as to BS7671 and get it signed by the client. Cover your back, that is the best you can do.