Tidying up lighting cables in the loft...

Andrew · Post by **Andrew** » Wed Mar 21, 2007 9:17 am

I'll be sorting out the loft soon, adding further insulation, etc.

In doing this, I guess I'll probably come across some lighting cables that need to be re-routed over existing insulation (!), as well as along joists, etc to be neat and out of the way of hazards.

My questions:

1) Do I simply use 20amp junction boxes to extend cable runs where I need to add length to the cable?

2) Does any of this come under the heading of part P? I won't be adding any lights, etc. Or can this be done safely without anyone needing to be informed?

Many thanks.

Post by **ultimatehandyman** » Wed Mar 21, 2007 9:25 am

As far as I am aware there is no need to inform building control.

Rather than use junction boxes can you not just use a longer piece of wire and replace the existing wire? This should be cheaper then using more junction boxes!

If you can't then you can use junction boxes, but you must be able to access them

Andrew · Post by **Andrew** » Wed Mar 21, 2007 11:56 am

That's a thought - I'll have a think about that one. I guess it depends on how much wire is needed.

If I do need to use a junction box at times, it is 20amp though, right?

Thanks.

Post by **ultimatehandyman** » Wed Mar 21, 2007 12:45 pm

Take a look at the fuse protecting the circuit, it will either be 5 amp or 15 amp, so if the fuse is 5 amp you could use 5 amp junction boxes although 20 amp junction boxes make it much easier to get the wires in as there is more room

sparkydude · Post by **sparkydude** » Wed Mar 21, 2007 8:05 pm

I hope for your sake that your lighting is not on a 15A fuse, a bit too much juice for the cables for my liking. It is more likeley to be a 6 or 10A fuse or breaker. If i was you as Chez says replace the cable with new longer lengths if necessary a lot easier than just adding junction boxes. remember the more junction boxes the more connections, the more likeleyhood of a loose connection and problems.

Nick

Andrew · Post by **Andrew** » Wed Mar 21, 2007 8:30 pm

The fuse for the lights is a 5amp one.

Re just replacing cables and not using J. boxes: not that I've studied lighting systems yet, but what if the first wire isn't long enough? That goes all the way down to the consumer unit. If I needed to extend that one, I'd need to cut in a junction box and run new wire from that to the first light???

If so, 20amp is quite safe, yup?

Also, if you can use 1 or 1.5mm cabling, what's the difference? Can you interchange, or would you have to use all the same?

Thanks guys.

Post by **ultimatehandyman** » Wed Mar 21, 2007 8:56 pm

As you have a 5 amp fuse 1mm wire will be ok. If you had a larger fuse then you would need 1.5mm.

You can use 1.5mm on a 5 amp circuit, but you can't use 1mm on a 15amp circuit.

Joe · Post by **Joe** » Thu Mar 29, 2007 10:10 am

Hi great site, just a quick question about the re-routing of cables in the loft, i am helping my nephew this weekend boarding the loft, some of the lighting cables are just laying straight over the top of the joists, would i be better replacing the wires and drilling a hole through the joist for the cable or just cutting a notch and sitting the cable in that?

Thnx

jason123 · Post by **jason123** » Thu Mar 29, 2007 11:13 am

You can drill a hole through the joist, cut out a wedge, slip cable into hole and replace wedge securely.

Joe · Post by **Joe** » Thu Mar 29, 2007 11:20 am

thanks jason,

much appreciated.

Rich-Ando · Post by **Rich-Ando** » Thu Mar 29, 2007 9:46 pm

jason123 wrote:You can drill a hole through the joist, cut out a wedge, slip cable into hole and replace wedge securely.

personally i wouldn't advise that. loft joists are less than half the size of the ground/1st floor joists.

if you have to do it then make sure you drill your hole in the centre of the joist as stress is 0 rated at that point. cutting a slot out of it will weaken it and correcting it is usually not done properly.

ps. if you do ever find a 15A fuse/mcb on your lighting circuit, remove it instantly and insert the correct one, a 6amp mcb or a 10amp one if it's 1.5mm cable installed.

5Amp joint boxes are usually only any use for 12v spot light connections. they are too small and tend to leave your cables crammed. a 20amp jb is by far the easiest and neatest method.

sparkydude · Post by **sparkydude** » Fri Mar 30, 2007 7:17 am

Another thing to bear in mind, if your roof is constructed from roof trusses, held together with those gang nailed metal plates at the junctions, then cutting wedges or driling holes in them could quite possibly weaken the structure of the roof. All roof truss manafacturers clearly state in their information, that no notches or holes should be drilled in them .

Nick

Joe · Post by **Joe** » Fri Mar 30, 2007 8:31 am

Thanks for the advice guys i think i will leave the drilling/cutting the joists.

Post by **ultimatehandyman** » Fri Mar 30, 2007 8:50 am

You can always add some more timber on top of the joist and notch this out! Screw the timber ontop of the existing joists and then screw the boards into this