New sockets

[Andrewr4]

Hi
I've created a new small room by partioning a bit off 2 adjoining rooms. I want to add some sockets and have a couple of options:

1) Run a spur.. or spurs off an fcu. But I don't have the ability to test the socket I want to come off is on the ring main, although I believe it is.

2) I have a 6mm old shower cable which currently just runs a bathroom 2kw heater used occasionally. The shower is no longer electric. Can I also run this into an fcu (is that even necessary) fused down to 13A and then run multiple spurs into the new room.

Any thoughts?

Thanks

 

[ericmark]

The testing of electrical work is a problem with DIY, most DIY people simply don't have the equipment even if they have the skill. Theory we should simply say don't DIY, in practice people will DIY so giving some guidance seems the right thing even if not 100% correct.

So you need to be able to "bell out" cables, we call it bell out because in the old days people actually used a battery operated bell. So as long as you have RCD protection, if not then you really do need an electrician, then with the power off, (Main isolator or RCD as a MCB does not turn off neutral) then you take each pair of wires part them and test with multi-meter to see if connected, then also test between the pairs to see not connected, this is why main isolator if you only switch off MCB it will show neutral connected to earth.

Once you have verified it is a ring the next is to decide how to extend, using a grid plate and a pair of sockets you can turn a double socket into two singles without swapping back box, then you can extend the ring from that point, or you can fit a single socket a switch and a fuse in the plate so you have one switched socket and a fused spur, in theory you should test the loop impedance, the EZ150 costs under £50 and will test the loop impedance however the first light is 1.5Ω the pass for ring is 1.38Ω so to get a meter able to give you a figure rather than pass/fail the price jumps, to a point where likely cheaper to get an electrician to do the job.

Even the firms can get the testing wrong the link shows how it was a combination of plumber, plaster and electrician which caused the accident, and the guy blamed did not even go to the site. The person who did the testing got it wrong and the foreman was blamed for sending a semi-skilled man to test it. The main point however was the electrician doing the wiring did not really make a mistake, it was the plasterer who connected the line to metal work, so it does not matter how good you are at installing with so much going on it really need testing.

This happened before RCD protection today one would hope the RCD would trip, but again the tester for the RCD is over £100, you could do the work then get an electrical installation condition report done, however not sure if that would then save you any money?

So the point is however you do it there is a risk, and you need to assess the risk, and decide if it's worth it.

 

[Andrewr4]

Thank you for your reply, that's helpful. I do have RCD protection on all sockets, just not on lights. I'm told I have a split board (16th edition). I also have a multimeter so should be able to complete the test you suggest.

Failing the above what do you think to a radial circuit using the 6mm old shower cable? Would that need an fcu down to 13A to run 2.5mm to the sockets as I believe it's on a 32A mcb.

Thanks

 

[JohnW2]

Failing the above what do you think to a radial circuit using the 6mm old shower cable? Would that need an fcu down to 13A to run 2.5mm to the sockets as I believe it's on a 32A mcb.

It would not be acceptable to have 2.5mm² cable protected by a 32A MCB, but you would not necessarily have to fuse down to 13A. If 20A was sufficient for everything on that circuit, then you could have the MCB changed to a 20A one. In fact, depending on how the 2.5mm² cable is installed (e.g. whether or not buried in thermal insulation), a 25A MCB (if one is available for your CU) might well be a possibility.

Simply fusing down to 13A (with an Fused Connection Unit) for the new sockets would, of course, be acceptable, but you would then obviously be limited to a total of 13A for all the new sockets.

Alternatively, if you wired your new sockets with 4mm² cable, then the 32A MCB would probably be fine.

Kind Regards, John

 

[winston1]

Failing the above what do you think to a radial circuit using the 6mm old shower cable? Would that need an fcu down to 13A to run 2.5mm to the sockets as I believe it's on a 32A mcb.

Thanks

No FCU required. Run a ring from and back to the point on the 6mm cable. Known as a lollypop circuit.

 

[Andrewr4]

It would not be acceptable to have 2.5mm² cable protected by a 32A MCB, but you would not necessarily have to fuse down to 13A. If 20A was sufficient for everything on that circuit, then you could have the MCB changed to a 20A one. In fact, depending on how the 2.5mm² cable is installed (e.g. whether or not buried in thermal insulation), a 25A MCB (if one is available for your CU) might well be a possibility.

Simply fusing down to 13A (with an Fused Connection Unit) for the new sockets would, of course, be acceptable, but you would then obviously be limited to a total of 13A for all the new sockets.

Kind Regards, John

Sounds good. Does the same apply re mcb rating if the 2kw heater also continues to run off the 6mm cable?

 

[JohnW2]

No FCU required. Run a ring from and back to the point on the 6mm cable. Known as a lollypop circuit.

Yes, that's yet another possibility - but, depending on the topology of the sockets, it might actually be cheaper on cable to just extend the radial with 4mm² cable than to wire a 2.5mm² 'secondary ring'.

Kind Regards, John

 

[Andrewr4]

No FCU required. Run a ring from and back to the point on the 6mm cable. Known as a lollypop circuit.

Interesting, I did wonder about that but wasn't sure if it was ok. Sounds like th best option then if within the regs. Presumably the 2 ring connections just join the 6mm cable in a junction box. Also ok with the 2kw heater, which is fused down to 13A already?

 

[Andrewr4]

Yes, that's yet another possibility - but, depending on the topology of the sockets, it might actually be cheaper on cable to just extend the radial with 4mm² cable than to wire a 2.5mm² 'secondary ring'.

Kind Regards, John

Total cable length would be about 10m to make a ring. 5m radial.

 

[JohnW2]

Sounds good. Does the same apply re mcb rating if the 2kw heater also continues to run off the 6mm cable?

Well, that 2kW heater will account for about 9A - so if 11A was enough for the rest of the sockets then a 20A MCB would do (or 16A if you could use a 25A MCB).

However, you may have missed the point I added about possibly using 4mm² cable - or, indeed, winston's suggestion. Either of those approaches would make a full 32A available for sockets (plus heater).

Kind Regards, John

 

[JohnW2]

Total cable length would be about 10m to make a ring. 5m radial.

Price wise, the difference would be fairly trivial. At TLC 'per metre' prices (excluding VAT), 5 metres of 4mm² would cost £7.50, whereas 10 metres of 2.5mm² would cost £9.50).

Kind Regards, John

 

[EFLImpudence]

Total cable length would be about 10m to make a ring. 5m radial.

So - not much point having a ring, then.

 

[Andrewr4]

Well, that 2kW heater will account for about 9A - so if 11A was enough for the rest of the sockets then a 20A MCB would do (or 16A if you could use a 25A MCB).

However, you may have missed the point I added about possibly using 4mm² cable - or, indeed, winston's suggestion. Either of those approaches would make a full 32A available for sockets (plus heater).

Kind Regards, John

Thank you. Sounds like my best option is to leave the 32A mcb and make a secondary ring off the 6mm cable using 2.5mm as I do already have this.

 

[JohnW2]

So - not much point having a ring, then.

No, but if the OP wants the full 32A available, he would have to use 4mm² cable for the extension to the radial - and he says that he already has 2.5mm² cable.

Kind Regards, John

 

[JohnW2]

Thank you. Sounds like my best option is to leave the 32A mcb and make a secondary ring off the 6mm cable using 2.5mm as I do already have this.

I see nothing electrically wrong with that, and only fractionally more expensive in terms of cable.

However, I would 'warn' you that, since a 'lollipop' circuit is very uncommon, it might confuse some electricians (particularly 'electricians'!) who inspected the installation in the future, and some might even believe (I think incorrectly) that it was not compliant with regulations. If you do go down this route, be sure that it is well documented, and also make sure that the join between the 6mm² cable and the new ring is easily accessible, since full access to that would be required for testing.

Kind Regards, John