Wiring up an external security lamp

[Chris Learmouth]

I have purchased an external security lamp (with PIR sensor) from FOCUS. I have two questions:
1. Can I wire it up from one of the round junction boxes found under my upstairs floorboards? I have checked that the junction box is for lights only.
2. What wiring should I use? I have some 2 core, 23amp cabling but I'm not sure I should use it. It has written on it "BASEC TO BS6004 6242YH 2x2.5+1.5 SQMM ALTIN 2005 4".
As always, any help will be greatly appreciated.
Thanks.
Chris

 

[1974stephen]

You can wire this from lighting circuit JB, but it would be advisable to wire to a 3A FCU first before the lamp with PIR. The cable you are describing looks as though it is 2.5mm twin & earth, normally used for ring and radial power sockets. The normal cable for lighting is either 1 or 1.5mm twin & earth. The 2.5 you've got will do, it might just be a little fiddly getting it in the connections of the existing JB and also the light fitting. The other thing you have to bear in mind is that some idiot might come along and wire more sockets off the live side of the FCU thinking its on a socket circuit and not lighting. I would stick to buying some 1 or 1.5mm cable. It's only £12/100m from a trade counter or a few pence pr meter more when bought by the meter from B&Q.

 

[Chris Learmouth]

Thanks for answering my questions and you're right about the 23A cable size. But can you please explain what a 3A FCU is, is it some sort of circuit breaker? Just out of interest would wiring direct from the JB to the lamp make the lamp inoperative or something more serious?
Thanks again.

 

[1974stephen]

A 3A FCU is a 3 amp fused connection unit or a fused spur as they are sometimes call. They cost around £5.00 from B&Q etc.

This is basically a double pole switch with a built in 3A fuse.

This will provide a easy means of isolation for the light for any maintenance work, and also mean that in the case of a fault the 3A fuse in the FCU will go before the 5A or 6A fuse in the consumer unit.

You can wire straight from the JB, and it won'tcause any problems, but it is best practice to go via a FCU.

 

[Chris Learmouth]

Message understood and thanks again. I know what I'll be doing tomorrow morning...as well as the other countless jobs to be done!

 

[Steve]

is this a floodlight fitting? these are designed to take flex. Can you get hold of some arctic flex? If so, this will be much easier to feed into the gland in the lamp. I installed one recently, and it had about .75cm between the inlet and the terminal block, and i wired it with 1.0mm² cable, this was still very tricky. Flex is much more forgiving if it is too long, it will curl over.

 

[Chris Learmouth]

Stephen, fitted as per your instructions and everything works perfectly except....unit only works when the kitchen lights are switched on! Someone suggested to me (and I quote):
"You need to find, (or rewire), a junction box that has a full time hot wire, not a box that goes totally dead when a light switch somewhere is turned off."
As far as I am aware the junction box doesn't go "totally dead" as there are other lights connected to it and they still work when the kitchen lights are switched off.
If possible would still like to run the unit off of the junction box that I have been using because wiring is all in place. I'm not an electrician but like to have a go. But if's going to be a complex fix then I think I should call in a qualified spark.
Your assistance, as ever, is greatly appreciated.
(Crafty, thanks for advice about Arctic Flex, but couldn't find any so used the usual 1mm.)

 

[1974stephen]

how many connections are there in the JB? If there are four - red, black, earth and another red, or if you've got new harmonized cabling brown, blue, earth and another brown then swop between the red or brown you've connected to and the other.

In a JB, there are likely to be a permanent live and also a switched live. You've connected to the switched live, which is the switched live for the kitchen lights!

 

[Chris Learmouth]

Yes, JB has 4 connections with a combination of blues, browns, blacks and reds. Did as you suggested and moved the brown to another connection. Unit now works perfectly with no exceptions!
Thanks again.