adding a loft light from a socket junction box

[soloheadbeg]

Hello. I am planning to wire a light in the loft. There is a socket junction box (2.5 mm) in a convenient place. Can I take 1.5 mm live an 1.5 mm neutral (single core in each case) from the socket junction box to a switched fused connection unit (fitted with 3A fuse) and continue from there to the light fixture with 1.5 mm live and neutral again?

Thanks

 

[sparkwright]

You are better off checking first the junction box is suitable for spurring off (ie not already a spur if a 2.5 mm/30 amp ring).

If suitable run a 2.5 mm twin and earth cable to a switched fused spur with a 3 or 5 amp fuse. From here run a 1.0 or 1.5 mm twin and earth cable to the light.

You could always take the feed from a nearby lighting circuit. You will connect into perm live, neutral and earth.

Single core cable seems a bit of an effort. It would have to be double insulated. Twin and earth is a better job IMO.

 

[soloheadbeg]

Thanks for answer. Assuming the junction box is ok to use would it be dangerous to use the 1.5mm from the junction box to the switched fcu if the load would not exceed 300 W?

 

[JAmmmmm]

Thanks for answer. Assuming the junction box is ok to use would it be dangerous to use the 1.5mm from the junction box to the switched fcu if the load would not exceed 300 W?

Yes it would because someone may use it for something different in the future without checking the cable. If it's a socket circuit then more than likely either protected by a 20 or 32 amp mcb/30A fuse so the 1.5mm cable is not protected as it's only rated up to 15A.

 

[securespark]

Strictly speaking, don't the regs imply you can use a smaller CSA cable as long as it is fused down within x metres?

Otherwise all tails would have to be 25mm2...

 

[soloheadbeg]

Thanks all. So if I use 2.5 mm from the junction box to a 3amp fused connection unit (switched) it should be safe?

 

[JAmmmmm]

Thanks all. So if I use 2.5 mm from the junction box to a 3amp fused connection unit (switched) it should be safe?

Yes, as long as the junction box is suitable to spur off and it doesn't already have a spur branching off from it, which if there are 3 cables going into it on a ring final then there is.

 

[soloheadbeg]

Hi again. Have checked the lighting circuits in the loft and have discovered that though each of the three circuits is fed by live 1.5mm2 cables, the neutral 1.5mm2 cable for each circuit is connected to the nearest socket junction box neutral.

Doesn't this mean that the sockets and the lights would both have to be switched off at the consumer unit if any work was to be carried out on either circuit?

Also was this standard practice in the very early 70's?

I presume because the lighting circuits fuses are in the live line in each case the lighting circuits will still trip if the load exceeds the 10 Amp fuse rating.

Because of the way the lighting neutrals are returning via the socket neutrals anyway there is no advantage to connect my proposed loft light to the existing lighting circuit?

All replies would be very welcome.

 

[MrTinker]

Thanks all. So if I use 2.5 mm from the junction box to a 3amp fused connection unit (switched) it should be safe?

Yes, as long as the junction box is suitable to spur off and it doesn't already have a spur branching off from it, which if there are 3 cables going into it on a ring final then there is.

Are you sure it is a ring final Although ring finals are not against the reg's, in Ireland radials are the norm. If it is a radial it should be protected with a, 16A or 20A mcb(etc.) and spurring of it should not be a problem.

 

[Risteard]

Although ring finals are not against the reg's, in Ireland radials are the norm.

Not strictly true. In the north of Ireland ring final circuits are the norm. In the south of Ireland radials would be more usual. However both are permitted throughout Ireland.

 

[soloheadbeg]

Thanks a lot. It is a radial circuit. Three cables - one from consumer unit, one to one room and the third to a second room. The socket in the second room is then connected through a 4 inch wall to a socket in a third room. Am I still ok to spur off the junction box? I don't really want to connect the loft light to the lighting circuit because of wht I said already regarding the lighting neutrals being connected to the neutrals in the socket junction boxes.

Cheers

 

[MrTinker]

Spuring off a radial is fine yes.

 

[soloheadbeg]

Hello again.

The cable (2.5mm2) from the consumer unit to the socket junction box is approx 15 metres in length. The cable to the two sockets fed from the junction box are approx 3.5 metres each and I've run approx 5.5 metres of 2.5mm2 from the junction box to the switched fused connection unit (3 A). This gives a total of 27.5 m of 2.5mm2 cable protected by 20 A fuse. What is the maximum length of 1.5mm2 cable can I run from the FCU to power the new loft light. I believe approx 30 metres is the maximum length of 2.5mm2 cable. But does this include any cable after the FCU?