Running a spur from a spur

[Blunda]

Hello

I am pretty sure this is not possible but would like to double check and find out any alternatives. It is a very old house and only has 2 sockets in the room, I would like to add another 2. the problem is one of the existing sockets is already a spur off the other. I am guessing it is not possible for me to run a spur off the spur then another from that spur? It is not possible at the moment for me to pull up the floorboards to add the sockets to the ring. I guess the only alternative is for me to run a long extension lead from one socket to the other side of the room? is there any alternatives? if not, can anyone suggest a neat way of using an extension lead?

Thanks

 

[ericmark]

If you use a fused connection unit which is really what you do if you use an extension lead as there is a single 13 amp fuse in plug than you can add multi sockets as a radial off the ring main. However then volt drop and earth loop impedance must also be considered and of course all new sockets must be RCD protected.
Eric

 

[Taylortwocities]

Are you sure that your 'old' house is wired as a ring? Many old houses had radials not ring finals. (We're heading back that way in 2008!)

For that circuit, at the fuseboard, can you say what size of cable it is , how many cables are connected at the fuseboard and what size fuse is protecting it.

 

[Blunda]

There is no RCD at the moment, but one will be fitted eventulay. when you say fused boxes im assuming you mean sockets with built in fuses?

I have had a look at the fuse box, All I can realy tell is it appears to have 3 red wires goining into it, one of which appears to be comeing from 2.5m sq cable, but I cant be sure as it is a bit of a mess, I cant make out much more than that. There are 4 fuses, one for lights, one for shower one for sockets but im not sure what the fourth one is for? they are single pin wire fuses and the socket fuse seems to be using 30amp fuse wire. I hope this makes sence?

I thought it was a ring as one socket in the room has 3 wires going into it (one is the spur) please let me know what you think the circuit is and whether I will be able to connect a spur from a spur? Is there any other way I can determin what circuit it is?

 

[ericmark]

If you were connecting a water supply up to a fridge to provide cold filtered water you would select a likely source then test to ensure it is potable water and not the hot water or central heating supply and it is no different with electrical sources.
Ring mains must be intact and it is very simple with a meter to test with power off at the socket with a meter as to if the ring is still intact.
If you look at the BS 7671:2008, Corrigendum (July 2008) http://www.theiet.org/publishing/wiring-regulations/updates/index.cfm you will see a diagram on how sockets can be wired.
As well as ring mains we also can have radial circuits and both can have 32 amp supplies although they use different size cable and also you can have radials on a 20 amp supply in all cases before adding one must ensure the other limitations are not exceeded.
It is so easy to make mistakes and to miss out some important check which if we were on site looking at the work we would never miss the whole idea of the forum is to guide someone with at least basic knowledge on odd items which are not included in the for reference area.
A fused spur unit or FSU is like a single socket but with just a fuse in it. There is also Switched fused spur unit which as name suggests has a switch as well and also a type with an RCD built in see http://www.screwfix.com/prods/14770/Electrical/RCDs/Powerbreaker-13A-RCD-FCU
If I wanted to add extra sockets in a house where there were no RCD’s in the consumer unit (Was called fuse box but now modern ones have MCB’s not fuses hence name change) then I would use a RCD-FCU to comply with the regulations.
Or I would change the whole consumer unit for one with RCD’s built in. The latter is not a DIY job.

Does that help
Eric