10 A fuse for spur off ring main

my guess something like

These take the same type of fuses as found in a mains plug.

The fuse would not have been fitted in the backbox of an existing socket.

You would expect that a fused spur box would have been used, looking rather like this:

and it should have been inserted into the existing ring circuit at the point the spur was added.

Good hunting!

Chris

You are absolutely right. I found out and was about to post to say "solved it" but I saw people have already responded.

It turns out that what I thought was a double surface-mounted mains socket was actually a single socket with a separate backing box alongside it that houses a fused switch with a tray containing a 13 A (not 10 A) fuse. My excuse is that I didn't take everything out of the cupboard to get a good look at the so-called double socket.

Now here's the weird bit. I removed the fuse and tested it, and it was fine. So I replaced it and there is now power to the sockets. All I can think is that the vibration of the spin-drier in the washing machine alongside had vibrated the fuse so it no longer made contact. At least I now know where to look if it ever happens again.

What is the actual regulation for a spur? I'm sure the electrician said that the maximum combined load for those sockets was 10 A, so I assumed that a fuse would be this value. Maybe it's one of those cases where the regulations say one thing but common practice does another thing. Are 10 A cartridge fuses even available?

It is perhaps more likely that the vibration has loosened one of the terminal screws. It would be a good idea to check that all the screws are tight.

John

As someone recently posted

In any case, why would it need a 10A fuse unless the spur was wired up with bell wire?

John

A spur can be either fused or unfused. The important requirement is that the cable can't be overloaded. So you do this wither by limiting the number of devices that can be powered from it, or you provide a fuse.

So an unfused spur can only have one single or one double socket. The nominal load for a double is traditionally assumed to be 20A, but a section of 2.5mm^2 T&E in plaster or surface mounted is good for up to

If you have more than one socket (singles or doubles) or other devices on the spur, then it must be fused. In which case that would normally be a 13A fuse. (which would limit the total load on the spur to 13A (and a bit!))

Why would I need a fuse for 2 singles? Where max load of 2 x 13A < 27A?

Because the spec says one single or one double socket as a spur can be unused, two or more sockets must be fused.

What spec?

Do you mean the 18th Edition Wiring Regs? Yet by design it can be shown

Yes. I have 1A, 2A, 3A, 5A, 7A, 10A and 13A fuses, if you need one.

Unfused.

yes, you can show that, still doesn't make it allowable.

The regs say I can design an implement a system if I take into account both fault and load conditions. In short, why am I not allowed 2 singles on a 2.5mm^2 if my design says it's safe?

You can do it, but it is not a standard circuit, so you would need to justify it in the context.

Nominal load for a single socket is taken at 13A, and 20A for a double - so that leaves some headroom for more onerous installation methods that might de-rate the spur cable. Two singles nominal load will be 26A, which will be ok in *some* cases.

Thanks, that is what I assumed. Having said that it's probably not good practice but then I've never been happy with assuming a 2-gang socket will only be loaded with a max of 20A.

I thought that followed from the way BS1363 tested sockets with 2 outlets with only 14+6 A loads for temperature rise. That is, the assumption is that the total load on average won't exceed 20A; and if the designer of the circuit thinks it might then they ought to fit more sockets.

Well minne is in the back of a spur box that is fitted in the wall before it gets to the sockets, but this was done a long time ago, so as regs seem to change like the wind, I'd guess this is probably not allowed these days due to some strange eventuality, like a camel may kick it or somesuch :-)!

Brian

I'm curious about 10 amp though. Surely you would fuse it as 13 amp if that is what its been spurred from. Brian