Extend ring main into new room

[MBK73]

We are looking at putting some extra sockets into another room, however an electrician we have spoken to has said we can possibly extend the ring main. He has mentioned about breaking the connection between the 2 circled sockets and extending the main that way, ie connect to socket then create loop of sockets back to next one. Is that something that is able to be done?

 

[ericmark]

Yes, but it requires test equipment to know if the existing ring is under the 106 meters permitted, and if extra can be added and still keep within the limits, so not really a DIY job to extend a ring final.

 

[MBK73]

Thank you. Is the 106 metres the total length of cable, or square meters? What about spurring off individual sockets(?

 

[Mottie]

Although 106 metres will be a f'cking big ring and yours looks nowhere near to that.

 

[MBK73]

I may just get him to put spur off 1 socket to a double socket. It is only for a couple of table lamps and maybe a TV if the kids want to go in there.

 

[MBK73]

Does the 106m include to and from CU, as room sizes are well under 106 square meters

 

[Murdochcat]

Why are you doubting the spark who has been on site?

 

[MBK73]

Because I don’t want to get ripped off when there may be an easier alternative

 

[Murdochcat]

Because I don’t want to get ripped off when there may be an easier alternative

Ask another spark to quote then.

Random internet advice does not trump eye on site advice

 

[FrodoOne]

Ring Circuit !
All Socket Outlets on the same RCD.
OMG

 

[ericmark]

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by: (iv) taking account of the total floor area being served. (Historically, a limit of 100 m² has been adopted.)

(i) Low voltage installations supplied directly from a public low voltage distribution system

3%​

5%​

(a) Type B circuit-breakers to BS EN 60898 and the overcurrent characteristics of RCBOs to BS EN 61009 rating (amperes) 32 ZS (ohms) 1.38

These are the bits we are looking at, so we assume 20 amp centre of ring final and 12 amp even spread, so Design current for circuit Ib = 26 amps, so the line - neutral can increase by 0.59 Ω and the line - earth needs to be over 1.38 Ω.

It is not so cut and dried, as the 26 amp is not written in stone, however one can't simply add to a ring final, without considering the volt drop etc.

Today there is little equipment which will have a problem with volt drop, and the earth loop impedance with RCD/RCBO protection is not so important, as long as over 300 Ω then considered stable. But still, the line - neutral needs to be under 1.38 Ω for the magnetic part of the overload to work within the required time.

The MCB/RCBO is 2 or 3 devices in one, there is a thermal part which can take ½ hour or more to trip with over current, and the magnetic part which will take a fraction of a second to trip, so the circuit needs to be designed, so a short circuit will cause enough current to flow to trip the magnetic side, typically a type B needs 5 times the thermal current settings, plus 5% to allow for volt drop.

The problem DIY wise is the cheap (£40) plug in testers are designed for radials not ring finals, so are set to around 1.8 Ω not 1.38 Ω so it needs the expensive (£200) tester to work with ring finals.

 

[EFLImpudence]

Does the 106m include to and from CU,

Yes, of course.

as room sizes are well under 106 square meters

The area is irrelevant; forget about it.

 

[Mottie]

Ring Circuit !
All Socket Outlets on the same RCD.
OMG

What’s wrong with that? We have four ring circuits in our house. Upstairs, downstairs, kitchen, ovens.

 

[EFLImpudence]

We have four ring circuits in our house. Upstairs, downstairs, kitchen, ovens.

What's right with that?

I doubt you have a ring for the ovens but, with the possible exception of the kitchen, (the U.K. special dispensation) ring circuits are not necessary nowadays (i.e since MCBs).

 

[Mottie]

I doubt you have a ring for the ovens

I definitely do. I have two 20A double pole switches (one for each oven) right next to each other with a short piece of cable connecting the two of them together to make a ring circuit. Both have a 2.5mm cable following the same path back to the consumer unit going to a 32A breaker.