More than 13A from fused spur

[mjb]

A la Part P, I probably won't be able to do this myself, but I do like to *understand*.

In a utility room a washing machine and dryer are both fed from a double outlet, which comes from a 13A fused spur off what I think (will investigate and confirm) is a ring circuit. The fuse frequently blows, which is not surprising given that other discussions here estimate the current from these appliances around 20A. The ring goes on to supply a wall light, and there is no possibility of other appliances.

As I see it these are the options :

1) First choice would be to extend the ring down to the double socket. However the cables are very tight, and are on the opposite side of the house from the consumer unit. The only practical way to do this would be to add two junction boxes and run cable between these to the socket. However these boxes would end up behind tiled plasterboard and would not be accessible - so I think that is not a good option. Alternatively could the ring be broken behind blank faceplates, thereby becoming accessible?

2) Add another fused connection unit near the existing one and add another socket. The FCU's would end up being very close. Does that matter?

3) Leave it as it is and not use both appliances together. Not easy with children.

Even if I am mistaken and it is radial, I believe equivalent versions of either option one or two could still be used?

[Owain]

A wall light should not be supplied from a power circuit without being fused down with its own FCU. Do you mean the fused spur goes on? Same applies, the wall light should be fused down to 3A.

Not permitted unless you use crimped connectors. In any case you may run into problems with the cable run not being in the permitted zones horizontal or vertical from visible accessories.

Yes. Or you could just use sockets.

It could matter. You should avoid high "point loads" on a ring circuit.

4) a double socket is permitted as an unfused spur from a ring circuit, if the circuit is wired in 2.5mm. Not necessarily the best of ideas as the current of washer and dryer could exceed 20A which is usually the max rating of a single length of 2.5mm. Also, double sockets are themselevs usually rated at 20A max.

If it is a radial you are permitted to branch off as you like without using FCUs. However you will be limited to 20A total on the radial circuit MCB if the radial is wired in 2.5mm cable. If you have a 30A radial it must be wired in 4mm cable. (These cable sizes are minima and may need to be increased for voltage drop or derating factors.)

Probably the best solution is to confirm that the existing FCU is a spur from a ring, remove it and extend the ring to two single sockets, one for each appliance. Fuse the light down separately.

Owain

[Dave Plowman (News)]

Ignoring the wall light, you don't need an FCU for a double socket spurred off a ring.

[mjb]

Apologies for not responding to end of thread. Can't seem to do it with Google.

Many thanks. Yes I forgot to mention that I had spotted the fault with the light, and was intending to have a separate FCU fitted for that.

I have confirmed it is a ring circuit - it comes from the downstairs sockets (with a separate ring and two radials in the kitchen, so total load not high).

I could extend the ring in the manner suggested - replacing 13A FCU with a socket or blank down to the two sockets and then back up to another.

My worry now is that the whole supply to the room could be a spur from the previous room. That will need careful checking, but if so would clearly put a different perspective on things. I could still put in a new FCU for the light to make things safe, but couldn't do anything else without extending the ring from the previous room. Out of interest how would an electrician check whether the supply is an extension of the ring (the utility room was added on by previous owners after house built) or a spur?

[Dave Plowman (News)]

I've often heard this said, but never actually come across it in maker's specs, etc.

It seems strange to me as the average punter expects a 13 amp socket to be a 13 amp socket, and in say a kitchen, it's quite likely a kettle could be on the same pair as a washing machine. Of course with this combination the likelihood of 20 amps being exceeded for long isn't great.

[Tim S]

Some are only rated at 13A total. IIRC MK published some tests of their own double sockets showing that they were good to about

19A or so total load. A few amps more and they were starting to cook to the point of going brown.

I've thought it a tad strange too. A multi-gang extension block is protected by a 13A fuse - but someone can in principle manage to plug 26A worth of load into a fixed double socket which will kill it is done for long enough.

As usual, (mostly) diversity saves the day, as in your last paragraph.

But you are right, no-one much is actually aware of this limitation and there is no protection against such overload.

Cheers

Tim

[cpvh]

To go back to the OP's qustions, I think the best bet would be to put in a dedicated circuit radial at 20/16A or preferrably ring at 30/32A for the area concerned. It may even make the job simpler (depending on access to cabling and route back to the consumer unit).

Failing that, I'd go for integrating a couple of FCUs into the existing ring (if ring it be), or connecting them separately to the existing ring.

[cpvh]

..... and to check if the "ring" is really part of the ring or is a spur off the next room, I can't think of any way except the time consumming one, disconnect from the mains (pull the fuse/throw the breaker and preferrably switch off the whole CU) and then remove sockets and use a multimeter on the ohms range to buzz out the circuit and work out where everything fits together. of course if you find (as in my house) that there is a socket on the other side of the wall with

3 cables attached to it, and subsequent investigation shows that one of them is live when the power is on and the other two dead, then you can pretty much surmise that the previous owners made a kind of mini ring which they connected to the socket in the next room (I have converted/downrated most of the circuits in my house as the previous ocuupants (builders!) made a habit of this sort of thing.