Fused Light Switch spurred from Mains Socket

2 Sep 2017
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United Kingdom
Hi there,

I'm sure this has been answered several times already, but I'm trying to spur a fused switch from a mains socket to a light.

From the little I have gathered so far, I have to make sure of the following:

  1. 2.5mm cable from socket to fused switch
  2. 1.5mm cable from fused switch to light
  3. Change fuse on switch to 5amp instead of 13amp

Do I need to spur onto an FCU and then from an FCU to an unfused light switch then to light?

Or can I go directly from socket to fused switch to light?

Many thanks in advance.
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1. You should also check that the socket you are spurring from is not already a spur, unless it is a fused one, in which case fine.
2. Or 1mm². It's no big deal - 1.5mm² will also be fine, and in fact is harder to break. Take no notice of anybody popping up who tries to tell you that using 1.5 will hasten the end of civilisation by wastefully using too much copper. Or quibbling that lights are also "mains".
3. Yes.

You can use the FCU as the switch for the lights if you want.

Is the circuit RCD protected?

You should be aware of the rules for where you may conceal cables. https://www.diynot.com/wiki/electrics:walls

Do I need to spur onto an FCU and then from an FCU to an unfused light switch then to light?

Or can I go directly from socket to fused switch to light?

To clarify what has already been told, if this is a 30 or 32amp ring circuit and the socket in question is an unfused SPUR, you would need to convert the socket to a 13amp FCU, then this will then supply both the socket and the 5amp switched FCU for the light.

If the socket is fed directly from the ring circuit, or you have a 20amp radial circuit, then you should be able to omit the '13amp FCU'.

Take no notice of anyone popping up who tries to tell you that there is no such thing as 5amp FCU, I have only written that to distinguish between the two FCUs.
Thanks for the replies.

The socket is unfused, but Pretty sure it’s on the main ring circuit as it’s a new build. It also has 2 wires going into the socket.

Is there any other way of telling it’s not a spur? Is it worth doing a resistance test?

Yes the circuit is RCD protected.

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You need to switch off the power and remove the socket then disconnect the two Line(live) conductors (and Neutral) and see if there is continuity between them - because, if it is a ring, they will be connected together at the CU.

Do you have a multimeter?
Yes I’ve got a multimeter - so do I test live to live, neutral to neutral and earth to earth?
Thanks all - it is on main circuit - connectivity is there.

My main problem now is I've got a flipping metal stud in between my socket and where I want to put the switch and light.

Any ideas of running cables past a metal stud?

As has been stated you don't need 1.5 mm for a light, 1.0mm is fine, cheaper and saves the planets valuable resources of copper.

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