Can you extend ring main this way?

[veedee]

I would like to extend my ring circuit.

Currently, two cables are going into existing socket

Can I

1. Remove one of the cables going into the existing socket

2. Run one new cable from existing socket to new socket

3. Add another cable from new socket back to the backbox in the old socket

4. Then connect the cable from number 3 to the cable from number 1 using wagos. Leaving them in the backbox
.

 

[winston1]

Yes, but if you are only adding one socket why not just spur it?

 

[veedee]

Yes, but if you are only adding one socket why not just spur it?

Because I'm being cheeky and actually adding five additional sockets

Didn't want to over complicate my original post.

Many thanks.

 

[ericmark]

I used the Screwfix LAP range of grid sockets so two single sockets in one double socket plate, but step one is measure the loop impedance, or use a low ohm meter and measure the resistance of existing cables, there are two limiting factors to size of the ring final, one is the volt drop, and the other is having enough prospective short circuit current to work the magnetic release part of the MCB, the thermal part is too slow with a short circuit.

For an electrician he has to have a loop impedance meter, so plugging it in to sockets considered likely to be around the centre of the ring final it is quick and easy to work out if there is likely to be a problem. It can be done without the loop impedance tester, a low ohm meter using at least 200 mA for the test is also permitted, as is enquiry, the latter means if you have a installation certificate or minor works or electrical installation condition report giving the readings, you can use maths to work out if the extra cable will take you over the limit.

However we tend to use the earth loop impedance only for each circuit, the line - neutral impedance or prospective short circuit current (in real terms they measure the same thing, ohms law is used to convert between the two) is not recorded on the standard form.

As to if with RCD protection the ELI is important or not, can be debated, as can the volt drop when using switch mode power supplies, but to the question can you extend, we should point out the correct way, even if you ignore it, unless you wanted to stay within the regulations you would not ask the question.

 

[veedee]

Thanks @ericmark

That's great info. Much appreciated.

 

[JohnD]

if you are interrupting a ring to run a loop to enlarge it, i'd say it's easier to use a Dual Box with two individual sockets in it.

though if you have access under the floor, or two sockets close together, you might be able to run the loop without having two ends in the same place.

is this a kitchen you're doing?

 

[veedee]

if you are interrupting a ring to run a loop to enlarge it, i'd say it's easier to use a Dual Box with two individual sockets in it.

though if you have access under the floor, or two sockets close together, you might be able to run the loop without having two ends in the same place.

is this a kitchen you're doing?

Thanks john

Can I ask, is having two ends of the loop in the same place undesirable? If so, why?

Yes, the wiring is for a kitchen. Did two ends of the loop in the same place give this away?

Utilising Dual boxes is good idea. Will bear this in mind when extending rings in other rooms.

 

[EFLImpudence]

Dual boxes are wider than doubles; you will have to remove the double and make the hole bigger.

What you originally suggested is fine.


Does the route to your new sockets involve the two cables running out and back by the same route or is there actually a need for it to be a ring configuration?

 

[JohnD]

if it's in a kitchen, and you are taking the sensible option of installing, on the wall 150mm above the worktop, a row of sockets, and switches for the appliances below, and the lights, boiler, TV and extractor above,

then it is very economical in labour and materials to chase out a cable groove, plus cavities for the backboxes, starting from one of the existing sockets. A dozen is probably enough. You can possibly connect to another socket at the other end, otherwise chase down to floor level and find the existing cable. There is a good chance you will be able to lead it up to the socket at the end of the row.

in a kitchen, a switch or socket every 600mm is not too many.

you can put a spur down to the appliances below, a single socket below for each, controlled by a DP 20A switch or SFCU above the worktop. in some cases a neon indicator is useful for things you may want to turn off.

a fuse in the FCU is, in reality, not a problem.

If you run the cable in oval conduit, it will be easy to cut into the row later and add more sockets when you find a dozen was not enough.

 

[Taylortwocities]

I disagree. A row of switches one for each appliance is mostly pointless. Appliances come with a handy plug. The trick is to find a convenient place for the sockets!