House Electrics Question?

Sir BoD

Well-Known Forumite
Hi All,

Can I run a spur from a FCU? The FCU runs a 6" kitchen fan, which is part of the ring main and not a spur itself. The spur would be for an outdoor light.

To add extra complication, it's all a bit tight with the FCU being right at the top of the wall snugly against the ceiling and I'm also concerned I won't physically be able to add more wires to the socket as there are already three of everything (Live, Earth, Neutral) going in and out already!

**Picture added. To the right of the FCU is some some plumbing which I'll be boxing in.

Cheers folks.
 
Last edited:

stoofer34

Well-Known Forumite
WACO.jpg
sounds like a job for WAGO


 
Last edited:

stoofer34

Well-Known Forumite
Could you fit a Wagobox in the ceiling void or behind your boxing in? top picture will take 5 wires X 3 15 wires? or 4 x 3 12 wires
 

Cue

Well-Known Forumite
You can’t spur a spur, but you can spur off the ring once.

My somewhat ok understanding of household electrical standards is that you can extend more than that as long as you fuse spur the start of where you break into the ring. As in on the output of the fused spur, so the entire spur run is fused. However as that spur is on the ring that isn’t really necessary here (but you probably will want a switch somewhere or you’ll be changing the bulb with a live fitting, unless you intend to use that spur as the switch?)

Something about the regs assuming people like to overload their circuits so if you don’t fuse it to the capacity of the wiring then someone is going to melt their cable at some point because the spur is likely thinner? Technically you can extend a spur to another 10 sockets and it’ll work, until you plug electric heaters into all of them.

(Not a Spark)
 

Gramaisc

Forum O. G.
You can’t spur a spur, but you can spur off the ring once.

My somewhat ok understanding of household electrical standards is that you can extend more than that as long as you fuse spur the start of where you break into the ring. As in on the output of the fused spur, so the entire spur run is fused. However as that spur is on the ring that isn’t really necessary here (but you probably will want a switch somewhere or you’ll be changing the bulb with a live fitting, unless you intend to use that spur as the switch?)

Something about the regs assuming people like to overload their circuits so if you don’t fuse it to the capacity of the wiring then someone is going to melt their cable at some point because the spur is likely thinner? Technically you can extend a spur to another 10 sockets and it’ll work, until you plug electric heaters into all of them.

(Not a Spark)
If you plug 10kW of heaters into the average ring main you'll require 40 amps to run them, if they're only a kW each...

All that really matters is the current up the cable, if you're running a lamp off it, these days that's likely to be no more than about 30 watts and won't cause any real issue at all.
 

Cue

Well-Known Forumite
All that really matters is the current up the cable

Yeah that’s what I was getting at. If the cable on the spur is thick enough you can do what you like (not sure about actual code there though), but I guess generally spurs end up with thinner cables than the ring and so can’t take such a high load? Hence the fuse.
 

Gramaisc

Forum O. G.
Yeah that’s what I was getting at. If the cable on the spur is thick enough you can do what you like (not sure about actual code there though), but I guess generally spurs end up with thinner cables than the ring and so can’t take such a high load? Hence the fuse.
Even if the spur is the same cable as the ring, it's a spur, whereas the ring is effectively two cables of the same size. If you fuse the spur and use an appropriate cable, there is no practical issue.
 

Sir BoD

Well-Known Forumite
So, in my very simple head, is this workable in the (?) after picture? Where the circuit comes in and out from the FCU there is very little give in the cable length, if none at all. Cheers.
 

Cue

Well-Known Forumite
So, in my very simple head, is this workable in the (?) after picture? Where the circuit comes in and out from the FCU there is very little give in the cable length, if none at all. Cheers.

Outbound cabling left off presumably?

Looks like you’re just added to the existing ring here rather than tapping into the FCU for both live and neutral so you’re not actually putting a spur in I don’t think?
 

Gramaisc

Forum O. G.
So, in my very simple head, is this workable in the (?) after picture? Where the circuit comes in and out from the FCU there is very little give in the cable length, if none at all. Cheers.
Yes, but it might be easier/better with a junction box where you have the light-switch, and the switch running off that.
 

Sir BoD

Well-Known Forumite
Yes, but it might be easier/better with a junction box where you have the light-switch, and the switch running off that.
The Wago would need to be there @Gramaisc as I would be breaking the circuit in the 'Now' circuit and that cable is quite short with little give so would need the Wago just as an extension. Or am I missing an obvious trick? The cable coming out of the FCU and into the light switch would be a new added cable, if that makes sense?
 

Sir BoD

Well-Known Forumite
Outbound cabling left off presumably?

Looks like you’re just added to the existing ring here rather than tapping into the FCU for both live and neutral so you’re not actually putting a spur in I don’t think?
I can't logistically add anything further wiring to the FCU @Cue as it's in such a crowded space, so when Stoofer34 recommended a Wago box, that was the only logical way (well in my head) that I could think of ordering it. Happy to have a simpler / neater way of doing it!
 

Gramaisc

Forum O. G.
The Wago would need to be there @Gramaisc as I would be breaking the circuit in the 'Now' circuit and that cable is quite short with little give so would need the Wago just as an extension. Or am I missing an obvious trick? The cable coming out of the FCU and into the light switch would be a new added cable, if that makes sense?
Indeed, but the light switch just interrupts the live wire - you will need to have connections for the neutral and earth, too.
 

Thehooperman

Well-Known Forumite
The drawing looks like the light switch is being connected into the lighting (I presume) ring main which is incorrect.

You need to run the live out to the switch and back and then the incoming live from the switch out to the light with the neutral to the light connected to the ring neutral.

Not forgetting to connect the earths together.

So I think you would need a 3 way Wago for the ring live, another 3 way for the neutral, a 2 way for the light switch live and a 3 way for the earth connections.

I think you can buy a Wago lighting junction box which would allow you to break into the lighting ring main wherever you want to and thus not create a spur.

Hope this makes sense.
 
Top