Amp/Watt rating of a spur socket

[Danny89]

Hi,

I recently noticed someone I know was using an extension lead to power both a washing machine and dryer, this was notice due to the washer and dryer no longer having power and on further investigation the plug of the extension had set on fire (understandably..) and then blown the fuse.

I recommended having a second socket fit which has now been done, although I do understand this is not required for a single spur it has been wired through a 13 Amp rated FCU for added protection.

I have a couple of questions regarding this:

1: From what I understand, most modern properties will have a 15 Amp or 20 Amp rating for ring mains which power plug sockets. How can I check what rating of the ring circuit is?

2: If a socket feeds a spur does this then mean a 20 Amp circuit would safely supply 5 Amps per plug (2 x double socket) or, as a spur is wired in (theoretically - I think?) the same way as adding a junction box, does this mean each double socket can safely provide 20 Amps divided by the two outlets so effectively 10 Amps per socket for prolonged periods? E.g. Can the washer and dry now be run safely at the same time as they are on separate physical plugs even though it's from a spur?

3: The dryer alone is rated at 2400 Watts, I was previously advised that this would draw a maximum of 20 Amps however after looking online I found the following calculation
'Use this handy equation: Amps = watts divided by volts. For example: 2000 watts / 240 volts = 8.33 amps.' (Found at http://cadetheat.com/heater-amps) which means the dryer draws 9.58 Amps max and the washer draws 9.16 Amps max totaling 18.74 Amps max. Which advise should I follow?

And purely out of curiosity...
4: If a ring main is rated at 20 Amps, how can this safely supply the 10 sockets which are allowed in the regulations? I am obviously just misunderstanding how mains wiring actually works but I haven't been able to find the answer to this (probably asking the question badly...)

Thanks in advance for any help.

Kind Regards,
Danny

[big-all]

heeelllooo and welcome Danny89
ring main usually 30 amp
spur 20 amp [double socket maximum as well]
socket 13 amp max

[Danny89]

heeelllooo and welcome Danny89
ring main usually 30 amp
spur 20 amp [double socket maximum as well]
socket 13 amp max

Thanks for explaining, I'll go get them both plugged in then now I know the house won't burn down

[Someone-Else]

Ring mains are usually 32A (or 30 if you have an old re-wireable fuse) Nothing to say you couldn't have a lower rated ring, but what would be the point.

A spur, is when it is "tapped off" the main ring, the most you should have is One double socket, BUT you can have as many sockets as you like, PROVIDED you fit a Fused connection Unit first.

If you read the specs for a twin socket, it is designed to be able to supply 13A, for both sockets, not each socket (but you could have 13A on one socket and 0A on the other)

Regarding your question 4:

What 20A ring? lets say 32A ring. You can have as many sockets as you can fit (and i do mean as many as you like) you are only limited by floor space. One ring is supposed to supply no more than 100m squared. Again as many sockets as you like. (no really) This is so because it is assumed that not all sockets will be used at the same time / to the max.
Take a "modern" house, often the kitchen will have its own 32A ring because it is assumed that the toaster, the kettle, washing machine etc will be on at the same time. (Cooker not counted)

It is different in industrial / commercial premises.

In days gone by, each room had just one socket in the corner of each room, now look at it, each corner of each room usually has at least one twin socket in it.

[OnlyMe]

If you read the specs for a twin socket, it is designed to be able to supply 13A, for both sockets, not each socket (but you could have 13A on one socket and 0A on the other)

Not sure about that. BS 1363 rates a single socket at 14A and a double socket at 20A (with one socket tested at 14A and the other at 6A!)

However I would not want to try it. I spend enough time swapping sockets in old offices where they have had a 2kW heater plugged in for 8 hours a day.

[ericmark]

The ring final (not ring main that is something different) was invented during the end of world war2 to reduce the materials required for the massive rebuild ahead, over the years there have been some mods, including using thinner cable. So today we have a 32A supply to cable rated at 20A, but since feed from both ends that cable can carry 40 amp in the centre of the ring final.

However near the consumer unit it could in theory be overloaded, in practice even with 32A on a 20A cable it is unlikely to cause a problem, but the idea is that the load is even distributed around the ring final, and there is no heavy load for an extended time.

So the regulation book says that any fixed appliance needs to be calculated as to it's effect on the ring final to ensure no overload, it suggests to insure there is no overload any non portable appliance over 2 kW should have its own dedicated supply. This is exactly what happens with an immersion heater, and in the main also ovens, however dish washers, washing machines, and tumble driers are also in the main over 2 kW yet often they don't have a dedicated supply, if near the centre of ring there is not problem. However near the consumer unit they could cause an overload.

In real terms only the dryer function is a problem, although a washing machine uses 2 kW or more to heat water, there is not that much water in the machine, so the element is only on for a short time. So for tumble driers and washer/driers you do need to be careful.

The use of FCU does limit the power to 13A so no problem with fused spurs, and even with a double socket on an unfused spur although in theory you can draw 26A in practice unless you run two tumble driers from the same outlet the devices are not running long enough to cause a problem.

So if you ran a tumble drier and washer drier from same spur then likely there is a problem, but tumble drier and washer on same spur is unlikely to cause a problem.

[big-all]

to be fair i think most mass market driers and machines are now sub 2kw my last 2 or 3 have all been
indeed if i avoid the heating cycle on the washing machine the combined load off washing machine and tumble is around 2500w max
i worked out because the washing machine used about 0.75kwh [9p] over a 1hr cycle and the tumble 1.7kw[20.5p] so the complete wash and dry cycle for a full load was 30p to 90-99% dry
remember a tumble dryer will cycle between full /half/no heat as the clothes dry with less and less heat time as the closes dry

[Someone-Else]

remember a tumble dryer will cycle between full /half/no heat as the clothes dry with less and less heat time as the closes dry

That depends on make / model of tumble dryer. Most do not do as you say, but have a mechanical timer that turn the heating element off 10 mins before the cycle finishes to cool the element and over heat stat down.

[OnlyMe]

to be fair i think most mass market driers and machines are now sub 2kw my last 2 or 3 have all been
indeed if i avoid the heating cycle on the washing machine the combined load off washing machine and tumble is around 2500w max
i worked out because the washing machine used about 0.75kwh [9p] over a 1hr cycle and the tumble 1.7kw[20.5p] so the complete wash and dry cycle for a full load was 30p to 90-99% dry
remember a tumble dryer will cycle between full /half/no heat as the clothes dry with less and less heat time as the closes dry

There are not many washing machines about these days that you can avoid the heating cycle as they are usually cold fill only.

I bought a new washer in September to replace a 15 year old one. I am surprised how much longer certain washes take to do.
Apparently it saves energy to leave the clothes soaking in water for longer with the machine doing nothing for most of the time.

I doubt the new one will last 15 years.

[Kev888]

If you read the specs for a twin socket, it is designed to be able to supply 13A, for both sockets, not each socket (but you could have 13A on one socket and 0A on the other)

Not sure about that. BS 1363 rates a single socket at 14A and a double socket at 20A (with one socket tested at 14A and the other at 6A!)
However I would not want to try it. I spend enough time swapping sockets in old offices where they have had a 2kW heater plugged in for 8 hours a day.

I think the difference is because although a double socket is only 'a 13amp device', the BS 1363 test is supposed to simulate an overload condition - the socket must withstand it, but it isn't really intended in normal use. (There is also sometimes confusion over phrases like 'both sockets' - not meaning both 'at once').

TBH I've always found it very strange that a double 13amp socket is not actually intended to carry 2x13amps. How many homeowners would know that? As I understand it, the limitation is mainly about heat build up, so a toaster and a kettle wouldn't have time to make much difference, but obviously heaters can be a different matter. I hear that MK sockets will actually stand 2x13amps without becoming dangerous, but I know from experience that cheapo sockets (still to BS) can have pretty short lives even supplying 1x13amps, let alone 2x.