Extending an existing cable run

[pugsley]

Hi All, first time post so be gentle. My consumer Unit is situated under our stairs next to an outside wall. I currently have a 13amp two gang socket under the stairs, surface mounted. The boss lady now wants two further sockets situated near our front door on the same wall. Extending the cable from the existing sockets probably is not too difficult but I will have to go 'through' the bottom stair and then chase conduit into the wall to the new sockets. So..........is it permissible for me to go through the outside wall, along the outside and then re-enter where she wants the new sockets?

 

[Pete999]

Remember if the existing socket is a spur from the ring final circuit, you will need to install a fused spur before you add any more sockets to an existing spur (see appendix 15 BS 7671) as for going outside to run your cable, be aware of UV problems. If you don't appreciate what I'm saying then get an Electrician in to do the work, don't mean to be condescending but to many DIYers just daisy chain sockets as and when without adhering to the rules.

 

[pugsley]

Thanks for the response Pete. The existing socket is on a dedicated cable back to the CU so I assume I would not need a fused spur if I extended it internally? I take your point about using a qualified electrician though, especially as I don't have a clue what the UV problems may be!

 

[Pete999]

Well, what size cable, what size OCPD is used? the UV bit deals with the installation of cables outside, UV rays damage some types of wiring, makes it go brittle and loose it's insulation value is the best way I can describe it to a layman, take my advice, get a sparky in it shouldn't be expensive

 

[telectrix]

first question is what is the rating of the MCB supplying the existing under stairs socket/s, and is the circuit rCD protected? and for all the clever clogs out there, i do realise that that is 2 questions. and i worked that out without a calculator or google.

 

[pugsley]

Ok chaps, first things first! I now know what an OCPD is thanks to Google, and I'm guessing that it is the same as the MCB that telectrix mentions? In answer, I hope, to both posts the existing cable is 2.5mm and runs back to an MCB32 and the circuit is RCD protected. There is no way now that I will attempt the outside route, so assuming I extend from the existing sockets, do I need a fused spur? By the way, I intend to run the BT answerphone, a broadband modem and a home plug off the new sockets so I don't think the power draw will be all that high.

 

[Pete999]

Ok chaps, first things first! I now know what an OCPD is thanks to Google, and I'm guessing that it is the same as the MCB that telectrix mentions? In answer, I hope, to both posts the existing cable is 2.5mm and runs back to an MCB32 and the circuit is RCD protected. There is no way now that I will attempt the outside route, so assuming I extend from the existing sockets, do I need a fused spur? By the way, I intend to run the BT answerphone, a broadband modem and a home plug off the new sockets so I don't think the power draw will be all that high.

If it's a single 2.5 protected by a 32 amp cb, it should be a 20 amp

 

[pugsley]

With the load that I'm intending to put on it, is it a problem to leave it on 32 amp or should I swop it out?

 

[Pete999]

With the load that I'm intending to put on it, is it a problem to leave it on 32 amp or should I swop it out?

Standard 2.5mm2 radial 20amp cb

 

[Lucien Nunes]

If it's a single 2.5 protected by a 32 amp cb, it should be a 20 amp

If is is a spur from the ring, there will be two other cables in the MCB, but the B32 would be appropriate. However, it would not then be acceptable to daisy-chain another S/O from it.

You might know what you intend to run from it but someone else might connect a heater to each point.

 

[pugsley]

To all you guys that have responded, thank you. I'm overwhelmed by the speed you came back to me.

As the B32 was a spare on the CU I was assuming that it was not part of another ring. So, from what you are all telling me, I need to have the cable feed from a spare B20 and I cannot daisy chain out from the existing socket. Is that correct? I get the bit about plugging heaters in, by the way.

This just goes to show me how perilous DIY electrics can be when you don’t have enough in-depth knowledge of what you are doing.

 

[Lucien Nunes]

If the MCB is changed to 20A which it should be as Pete999 points out, then you form a radial circuit with the cable fully protected (unless the installation method requires further derating) and you may daisy-chain additional sockets.

 

[pugsley]

If the MCB is changed to 20A which it should be as Pete999 points out, then you form a radial circuit with the cable fully protected (unless the installation method requires further derating) and you may daisy-chain additional sockets.

Thanks Lucien. I now know what I need to do, or pay a sparks to do it properly! As a matter of interest only, what could of potentially happened if it stayed on the B32 feed with the extra daisy chain?

 

[Sintra]

Worst case scenario the cable could overheat creating a potential risk of fire.