Wall lights on a spur from ring circuit

[Kaymo]

Being doing some decorating/running speaker cables behind walls, and in the process have noticed that the wall lights are powered from a switch which is part of the the ring circuit for the sockets in that room.

This is effectively just an unfused switch with the cable for the light connected to it, so the only fuse for that lighting circuit is the 32 amp breaker in the CU.

Firstly, is this allowable, as to my limited understanding it doesn't seem safe?

And if not, is there anything I can do about it, such as replace the unfused switch with a fused one?

Thanks.

 

[EFLImpudence]

Technically it depends on whether the cable can safely cope with any fault current with the 32A MCB.

What size is the cable? The same as the ring circuit or smaller?


Replace the switch with a Fused Connector Unit if you want to.

 

[Kaymo]

The lighting cable looks a size down from the ring cable. I think that the ring cable looks like 4mm twin and earth, so the lighting cable might be 2.5mm.

I had been thinking that a circuit coming off a spur is usually fused, either with a fused switch, or by the fuse in the plugs if its a socket, but I suppose the only load is the light and the bulb will blow before anything else if there is a high current passing through, so maybe it doesn't matter.

 

[EFLImpudence]

The lighting cable looks a size down from the ring cable. I think that the ring cable looks like 4mm twin and earth, so the lighting cable might be 2.5mm.

4mm² T&E has seven strands; 2.5mm² T&E (and smaller) has only one.

I had been thinking that a circuit coming off a spur is usually fused, either with a fused switch, or by the fuse in the plugs if its a socket,

It is - usually - because people fit them to save working out if they are really necessary.
Perhaps the installer did work it out.

but I suppose the only load is the light and the bulb will blow before anything else if there is a high current passing through, so maybe it doesn't matter.

You are correct about the load; there won't be an overload so there won't be high current passing through the bulb.

The concern is a fault causing a short circuit, L - N, or a fault to earth, L - E.

It very likely will be fine but impossible to say for sure on the internet.

 

[plugwash]

I'm going to disagree with EFL here.

BS7671 sets a maximum protective device rating for many types of lampholders at 16a. While your specific light fitting may not have one of these lampholders I would consider the spirit of the regulation to be saying that regular lighting should be protected by a device of no more than that rating.

Personally I would replace the switch with a switched fused connection unit.

 

[Kaymo]

Thanks both for your replies.

Now while I am asking...

If I was to replace the light switch with a 16 amp fcu, could I also connect a socket to it. i.e. fused switch is on the ring main, with the socket and a light switch both coming off it, or am I talking crazy now!?

I only ask because now that I know that this switch is on the ring, its the perfect place for a spur socket for my a/v stuff!

 

[plugwash]

The highest rating of fuse you can fit in a FCU is 13A, personally I like to have smaller for lighting but it's not a regulatory requirement. Also the switch and fuse in a switched FCU are internally connected together.

A spur feeding one single or double socket doesn't need fusing though, so you can take the spur for your socket from the supply side of the FCU and connect your lighting to the load side.

 

[sparkwright]

How many cables are currently on the SUPPLY side of the switch?

 

[Kaymo]

A spur feeding one single or double socket doesn't need fusing though, so you can take the spur for your socket from the supply side of the FCU and connect your lighting to the load side.

Thanks, that's a great tip. That also makes me think that I could alternatively take the socket from the load side of the switch, then use that switch to turn all the AV equipment on or off at once, and I could just put a plug on the wall light cable and plug it into the same socket strip if I wanted to use it (I dont use the wall light much). The switch is in a really convenient location in arms reach of where I sit on the sofa so I might get more benefit from it controlling power to the AV equipment.

How many cables are currently on the SUPPLY side of the switch?

Just the normal two t&e cables that would be on a ring circuit, and the single cable for the lights is coming off the load side.

 

[EFLImpudence]

You also get two cables at each accessory on radial circuits - except at the final point.

 

[Kaymo]

You also get two cables at each accessory on radial circuits - except at the final point.

What would make you think its a radial circuit? My understanding is that radial circuits are rare in the UK.

A while back on another socket in the same circuit I measured 220V on both cables with the wires disconnected, so I took this as confirmation that it was a ring circuit.

 

[ericmark]

If I was to replace the light switch with a 16 amp fcu, could I also connect a socket to it. i.e. fused switch is on the ring main, with the socket and a light switch both coming off it, or am I talking crazy now!?

Screwfix LAP range do a grid system where a fuse holder, switch, socket, etc can be clicked into place with a single or double socket size back plate, so yes can be done, this socket at bottom had 13 amp socket, switch and fuse as an example.

 

[bernardgreen]

or use a dual box

and standard socket and FCU

 

[Kaymo]

Thanks for all the suggestions folks. I have a few options now.

I think I might run the spur from the load on the existing switch to a socket behind the AV equipment, so that I can switch the whole thing on and off from the sofa, then connect the light to the supply side of the existing switch via a new light switch and FCU with a 3A fuse. Neat solution with very short runs and easy access right now as I have the floor up and plasterboard open at points nearby.

That way I will be able to reach the wall light and a master switch for the AV from the sofa.

And if I lean over a bit I could open the window and get takeway delivered through there. I might never leave the sofa again.

Although I still need to put the room back together before I start my life of leisure!

 

[SUNRAY]

Sounds like you've got it sorted for a grand lifestyle.