Running mains supply into Loft?

[digiruss]

Hi all,

I'm looking to run a mains cable up into my loft - was thinking about running it from a fused connection box that is already connected up for my power shower pump. This box has a three amp fuse. The box seems to have two mains cables running into it so I asumed it is connected to the ring circuit. Is it OK to spur off this and if so is it ok to change the fuse toa 13amp?

Thanks

 

[andy]

youl have to add another spur to the ring. you cant use the existing spur as its only rated 3A and is for the shower

 

[digiruss]

Cool - thanks for that

 

[Steve]

digi said the FCU is on a ring. therefore he can spur off it on the supply side. the cables might be a bit tight though in the single back box.

 

[Damocles]

He said it had two cables. Check where the power is coming from! it could be one cable is off to the CU while the other is heading towards the immersion heater.

 

[Steve]

Sorry, the fact he said 2 "mains cables" told me it was on a ring, but i suppose one could be the supply and one the load.

Are they both connected to the supply/feed side of the FCU? If so this can be spurred off with a 3rd cable in the supply terminals.

 

[digiruss]

Thanks again all for the help.

Looking at the FCU - two sets of mains ring cable coming in from under the floorboards to the box - shower pump then wired into this box and a three amp fuse fitted. This was all fitted when new dorma installed last year (qualified electrician did the work).

So I take it that even if it is on the ring circuit - changing the fuse if I spur off to the loft is a no-no?

 

[breezer]

that is correct.

how ever no one says you can not fit an fcu on the ring side of the fcu, or you could even take the ring inti the loft, and put an fcyu up there for the lights (sockets being on the ring)

 

[Big_Spark]

If some of the supply is for lighting in the loft, why not simply take the supply for the lights off the upstairs lighting circuit, you can easily add one or two lights to this circuit without impacting on it's operational characterists too much. All you would need to do would be identify which is a permanent Live/Neutral feed at a cieling rose and run a cable from this (doddle), as it is only a loft light you could simply run this cable through a switch, Joint the Neutral in the back of the switch and connect the live across the switch.

As breezer has said, any sockets up there would then simply come off the ring and there is no problems with Spurs and fuse sizes etc.

 

[felix]

You can't put a 13 amp fuse in your existing FCU because whatever lies 'downstream' might only be rated at 3 amps. What you can do, in theory at least, is put a second FCU with 3 amp fuse in line with the pump supply. Feed this from the first one with 13 amp cable and you can have a 13 amp fuse in that.

This gives you 10 amps spare for your loft; enough for lights and maybe an aerial booster but not much else. That's why it's a bodge. If it was mine I'd be looking at a way to extend the ring or, failing that, I'd put a single socket on an unfused spur with 2.5mm cable.

If all you need is light it might be easier to tap into the upstairs lighting circuit but this has one drawback. You might want light in the loft while you work on the upstairs lights!.

Hypothetical question. Does anybody know whether you can have a single socket AND a single FCU on a spur?

 

[andy]

Hypothetical question. Does anybody know whether you can have a single socket AND a single FCU on a spur?

i would guess no, since you can then draw 26A, and depending on if the cable is thru insulation then you can overload it

 

[plugwash]

the regs don't say you can though especially if the fcu is running a small load (ie a fan or similar) i would consider it a minor fault at worst

afaict spurs with two single sockets used to be allowed but were disallowed in later versions of the regs because people were replacing the singles with doubles.

you could fit a second FCU so you had a fused spur supplying both the FCU and a socket

 

[digiruss]

I'm sorting power for lighting by using the existing cabling setup for upstairs lights - the idea about spur off the shower pump fcu was for a mains socket in the loft.

Sounds like I need to squeeze in another junction box to let me extend the ring into the loft and then connect the socket into that.

Cheers all - very helpful.

 

[Big_Spark]

Hypothetical question. Does anybody know whether you can have a single socket AND a single FCU on a spur?

i would guess no, since you can then draw 26A, and depending on if the cable is thru insulation then you can overload it

That would purely be dependant on how you connected it up, if the second FCU controlled the supply to the single gang socket then the answer would be an unequivical Yes.

 

[andy]

Hypothetical question. Does anybody know whether you can have a single socket AND a single FCU on a spur?

i would guess no, since you can then draw 26A, and depending on if the cable is thru insulation then you can overload it

That would purely be dependant on how you connected it up, if the second FCU controlled the supply to the single gang socket then the answer would be an unequivical Yes.

yes, i agree with that, but form the question, the FCU is fed from a spured socket which is then no