The previous owner of my house spliced the downstairs lighting circuit to power some outdoor heaters. They ran the twin and earth cable through the exterior wall, and wired it into an external switch to control the heaters. It was a terrible mess, I didn't trust it at all, and I didn't want the heaters anyway. So I've decommissioned the whole lot, and have temporarily spliced the lighting circuit back together inside a weatherproof junction box.

I'm now thinking I'd like to make use of this point to add a security light, but I want to do it properly.

What I have is a loop of cable coming out of the wall, about a metre long. (50cm up to the junction box, and back down again). My feeling is to replace the junction box with a fused connection unit (like this one). The security light doesn't really need a switch as it has a sensor, but I figured this was preferable to just wiring the security light into the junction box, and I wasn't sure exactly how to wire it in either.

If I use a connection unit like this, would I simply wire both of the cut ends of the original circuit into the supply terminals?

What would the preferred approach be? What else should I consider?

  • Make sure that the wiring used for the exterior run is approved for wet locations. Appropriate wet-location wire ratings are called for by the NEC in the US, and I'm sure the UK has equivalents.
    – FreeMan
    Commented Jan 10 at 19:20
  • "replace the junction box with a fused connection unit" - why? J-box has power and a neutral, right? Just hang the light. "I wasn't sure exactly how to wire it in either." - uh... then we're done here.
    – Mazura
    Commented Jan 11 at 2:55
  • @mazua could you post as your answer how to wire this without the need for the fused connection unit?
    – Tim
    Commented Jan 11 at 9:10

1 Answer 1


Your solution looks appropriate. But when you say "simply wire both of the cut ends of the original circuit into the supply terminals", you cannot just cram multiple wires into a terminal meant for one. Look up the proper method of splicing wires, and the minimum box size required for the number of wires, splices, and so forth, and then choose a box large enough to accommodate them all.

  • Thanks. Perhaps one small box to join the cut ends, then a single power cable to the outdoor fuse? Otherwise I'm looking at a pretty big box to house it all together
    – Tim
    Commented Jan 11 at 9:08
  • 1
    For the linked connection unit, multiple wires can be secured in a single terminal. The spec says "Terminal Capacity: 3 x 2.5mm2", meaning each terminal can secure 3 wires each of cross section up to 2.5mm2. Standard on a lighting circuit will be 1.5mm2, so fitting 2 will be no problem. This is standard for UK units
    – rhellen
    Commented Jan 11 at 11:20
  • Thank you. Looks like the twin and earth cables might be 1.0mm. Painted over, but some similar width cable I have says "2x1.0+1.0"
    – Tim
    Commented Jan 11 at 11:53
  • @rhellen good catch. The more I learn about Euro wiring practices, the more I like.
    – MadMonty
    Commented Jan 12 at 20:04

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