Light from FCU blowing fuse.

15 Jul 2006
Reaction score
United Kingdom
I am running a new light from a ring main socket. I have run 2.5 to a FCU with a 5amp fuse then 1.5 to a switch and from the switch to the light. When I put the fuse in at the consumer unit the light comes on but as soon as I throw the light switch the fuse blows in the FCU. I have double checked the wiring and everything is fine. Brown from ring to live in on FCU same with blue, earths connected flying earth to metal box. From FCU to L1 in switch and blue to com then on to light. Can anyone help, it would be much appreciated.
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Yes, you have wired it up wrong!

The diagram (like most queries) is on the WIKI

Your connections in the switch are wrong.

Brown (live) from FCU goes to COM on the switch
Brown (switched live from light goes to L1 on teh switch

You are then left with two earths. Sleeve them and join them in a bit of connection block

And two blues (neutrals) join them together in another piece of connection block.
I have double checked the wiring and everything is fine.
No it isn't.

From FCU to L1 in switch and blue to com then on to light.
So when you close the switch you connect live and neutral together.

You could well need a new one now.

But please - before attempting any more electrical work, spend some time learning about it. At the moment you don't even know what a simple switch does, and basically you are wiring things up with no idea of what you are doing and just hoping that you get it right.

That's a very bad basis on which to do electrical work - without a full and genuine understanding of how things work, of what you are doing and why you could put yourself and others in danger.
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Thanks for the replies, everything is working finr now. I will take more care in future and get a better understanding before attempting anything else and will get a professional in if I am not sure. Thanks

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