13A spur from 30A circuit

"bof" wrote | Anyone advise whether it is acceptable (i.e. within wiring regs) | to run a 13A spur to a couple of 13A sockets from a 30A cooker | point (which has a built in 13A socket).

No. The cooker circuit is intended for the cooker only. If you run a spur to a double 13A socket (which IIRC is rated at 20A) that leaves only 10A for the cooker and the 'kettle' socket. That is inadequate for the possible load on a general purpose circuit.

If you are not going to use a cooker on the circuit, you can run a spur, but you must either run it in >4mm cable as a 30A radial, or change the MCB to

Owain

So what cable size should a spur off a ring circuit be using, seeing that both a 'cooker' and a ring circuit are 'fused' at 30A? What am I missing / not understanding in your answer above...

He is actually incorrect. It is permitted to spur off a single or double socket in 2.5mm in most installation circumstances. However, it isn't best practice in case further sockets are daisy chained on to it by a monkey later. I would use 4mm or 6mm as suggested, even if technically permissible to use 2.5mm. This also applies to any socket spurred off a ring that, due to its location, may result in some spanner extending further, even if you won't yourself.

Christian.

permissible

But you could not physically do what you suggest, most of the terminals used on typical 13 amp sockets won't accept two 2.5mm wires and a 4 or 6mm wire (the situation is even worse if the old multi-strand (7 / 029 ?) cable is in use.

Surely safety is taken care of by the fuse or MCB, even if a hundred 13 amp sockets were added by some idiot the user could still only pull 30 amps from the circuit without tripping the fuse or MCB, 3 x 3Kw electric fires are still going to draw 37.5 amps [1] how and were ever they are connected to the ring circuit.

Yes, but 2.5mm cable might only be suitable for 20A (dependent of installation method), so it is required that the load won't draw that. A single socket is limited to 13A, whilst you should assume 20A for a double socket. Start to have multiple sockets and it would be easy to exceed the

Christian.

Well you learn something everyday, so some 2.5mm FT&E is suitable for use as a spur off a 30 amp ring circuit and some isn't......

Hek!

You miss the point. It's about temperature, what it is run in, etc.

Either I've missed something or you maths doesn't add up, a (double) 13 amp socket could need to draw 25 amps, two 3Kw load @ 12.5 amps on each outlet

No I haven't, but I suspect Christian has, re read his message(s).

"Jerry." wrote | > Yes, but 2.5mm cable might only be suitable for 20A (dependent of | > installation method), so it is required that the load won't draw that. | > A single socket is limited to 13A, whilst you should assume 20A for | > a double socket. Start to have multiple sockets and it would be | > easy to exceed the 20A cable rating without tripping the 30/32A MCB. | Either I've missed something or you maths doesn't add up, a (double) | 13 amp socket could need to draw 25 amps, two 3Kw load @ 12.5 amps on | each outlet

The 32A ring circuit was designed for general purpose use in the 1940s, and it would be quite unlikely to have 2 3kW heaters plugged in at the same point. Now it's quite possible for a washing machine and tumble dryer to be plugged into the same double point on a utility room spur, which is a failing of the person who installed a double socket spur into a utility room to anticipate the likely use of the installation.

Owain

"Jerry." wrote | Well you learn something everyday, so some 2.5mm FT&E is suitable for | use as a spur off a 30 amp ring circuit and some isn't......

I didn't say 2.5mm wasn't suitable as a spur off a 30/32A ring circuit. I said it wasn't suitable as a spur off a 32A general purpose radial circuit. There may as Christian says be cases where it is technically acceptable, but that is not one of the *standard* circuit arrangements recognised for 13A sockets.

In some cases you might be able to spur off unfused in 1mm (eg to an FCU in the loft you know will only ever be used for a very low current aerial amp) where the MCB provides short-circuit protection and the nature of the load (3A in the FCU) provides overload protection. In other cases 2.5mm will not be adequate.

It's important to realise that for 32A ring and 20A radial circuits, 2.5mm is the *minimum* cable size in the standard circuit arrangement, and you are not exempt from calculation to ensure a larger cable is not required.

Another approach to your question is that the 32A circuit is (a) already fully loaded by the cooker and should not have any further load added (b) a standard circuit arrangement for one appliance that does not admit of further addition.

Owain

Agreed. But that's what the regs allow. Double sockets are considered to be single ones for the purpose of calculations; it is 'unlikely' that both sockets would be required to supply a full 13A (the limits on floor area are a factor in this).

Christian's 'you should assume 20A for a double socket' is not his estimate, but what the regs effectively say.

I don't need to. See my other message.

I was under the impression that a double socket was rated 13 amps max, not for each socket?

Trevor Smith

First as the OP, thanks for all the replies, wasn't expecting quite so much discussion to come out. Maybe I need to be clearer about the actual installation:

Currently there is a 30A circuit feeding a cooker point with built in

MTIA

I know you didn't, but you implied that because it was 'fused' (MCB) at 32 amps 2.5mm wasn't suitable, I asked what the difference was between a spur off a 32 amp radial and a 32 amp ring circuit.

But that is not what was said, you told the OP that he should use ">4mm cable as a 30A radial, or change the MCB to 20A and you can then use >2.5mm cable as a 20A radial", which is not the same as you have said above. the OP might only need to place an additional socket next to the 'cooker' switch - there would be no additional temperature or length of cable run to calculate. I know of a situation were a built in oven in supplied via a 32A DP switch and a single 13 amp socket is supplied via a spur from the (radial) 32 amp (cooker) circuit to supply the built in microwave oven (which is above the oven BTW) - both are isolated if the 32A DT switch is off. Both outlets are within 24 inches of each other. Are you saying that this is wrong?

As for a spur off a ring circuit, if there is a danger that someone in the future might add further sockets (the daisy chain that was mentioned by Christian) to the spur surely the *correct* approach is to extend the ring circuit rather than install a spur. Surely the size of cable reflects length of circuit and how and where it is run, not the load - which (for power circuits) should be assumed as maximum IYSWIM?

Well yes, and I would assume that people would calculate such loading, but if it was not done the MCB (or fuse) would provide the safety required surely.

What is the power rating of the cooker, (or hob and oven)?

Christian.

"Jerry." wrote | "Owain" wrote | > "Jerry." wrote | > | Well you learn something everyday, so some 2.5mm FT&E is suitable for | > | use as a spur off a 30 amp ring circuit and some isn't...... | > I didn't say 2.5mm wasn't suitable as a spur off a 30/32A ring circuit. I | > said it wasn't suitable as a spur off a 32A general purpose radial | circuit. | I know you didn't, but you implied that because it was 'fused' (MCB) at 32 | amps 2.5mm wasn't suitable, I asked what the difference was between a spur | off a 32 amp radial and a 32 amp ring circuit.

The difference is that a spur off a 32A ring cannot be used to supply further sockets. A 'spur' off a radial circuit can be, and must be suitable for the full circuit loading. A 32A radial must be wired in >4mm and that means the entire circuit.

| But that is not what was said, you told the OP that he should use ">4mm | cable as a 30A radial, or change the MCB to 20A and you can then use

| cable as a 20A radial", which is not the same as you have said above.

Those are the two standard circuit arrangements for radial circuits feeding

| I know of a situation were a built in oven in supplied via a 32A | DP switch and a single 13 amp socket is supplied via a spur from the | (radial) 32 amp (cooker) circuit to supply the built in microwave oven | (which is above the oven BTW) - both are isolated if the 32A DT switch is | off. Both outlets are within 24 inches of each other. Are you saying that | this is wrong?

It depends exactly on how it is wired, and it isn't a standard circuit, but it sounds acceptable. However, the difference is that this circuit is supplying only 2 appliances.

Owain

In message , Christian McArdle writes

I don't know, it's a Belling 600X, the documents for which disappeared long ago.