Clarify spur

[andrew299]

Hello everyone,
I would just like someone to check this through just to check I've not missed anything.

What I want to do is run a spur off of a double socket on the ring main (i've checked it is not a spur or feeding a spur already) to a new socket on the other side of my chimney breast.
First question - Can I put a new double socket here or will it only support a single?
I will be using a 2.5mm cable to go under the floorboards and loop back up to the new socket.
I want these new sockets (using a short extension lead) to be able to power a TV, DVD player, Video and digibox. Second question - Would this be too much for a spur?
Thanks
Andrew299

 

[Adam_151]

A spur can be a double or a single so no problems there, and home entertainment equipment doesn't take much power, so there will be no problem with using the spur in the way in which you describe

oh, and while you have the ring off would be a good time to verify continuity on all three ring conductors

 

[andrew299]

"oh, and while you have the ring off would be a good time to verify continuity on all three ring conductors"

Could you please expand on this?
Thanks

 

[Qedelec]

What Adam is suggesting is fairly simple.
The ring main is, as its name suggests 'a ring' and although it should be continuous, it has been frequently known to have a break in it. This is not a problem normally but should someone try to draw the max current from a socket that has one 'leg' only connected to the fuse, there is a chance of overloading the cable.
With the power off and the socket disconnected from the circuit, make sure you have continuity on all three rings, Phase, Neutral and CPC. The reading should be in the low hundreds of Ohms.

 

[ban-all-sheds]

The reading should be in the low hundreds of Ohms.

Worst case will be the cpc. 1.5mm² has a resistance of 12.1mohms/m.

Low hundreds implies a cable in the 10's of km length - unlikely.

Also - Andrew - if you have access to the cables under the floor like that, why not put the new socket on the ring?

 

[Qedelec]

Worst case will be the cpc. 1.5mm² has a resistance of 12.1mohms/m.

Low hundreds implies a cable in the 10's of km length - unlikely.

Thank you ban, as always you have seen my deliberate error.

 

[JohnD]

oh, and while you have the ring off would be a good time to verify continuity on all three ring conductors

Good tip, I'll make a mental note to do that whenever I have a ring socket off.
Forgive my ignorance, but if
Worst case will be the cpc. 1.5mm² has a resistance of 12.1mohms/m.
then should I expect a ring of 20metres to have a resistance in the order of 242 milliohms, 0.24 Ohm, or have I not got the hang of this? Do you not have to make an allowance for all the terminals at sockets, or are these negligible resistance?

 

[kai]

Invest in a copy of the GBP 16 brown Onsite Guide, and read it thoroughly before undertaking electrical work - it outlines the testing procedures for the Ring Final Circuits in there too.

 

[JohnD]

You've caught me, I've only got the BLUE OSG and didn't fancy doing all the ring circuit testing from the CU - I thought continuity testing at a socket (e.g. when replacing a cracked one) would be a useful task to add (wouldn't you agree?)

Remember that at this point I'm not installing a new CU or circuit.