Chris Pearson: 
I have just checked. Drier is 2850 W and washer 2400 W.

I have no idea how often the drier's thermostat will cycle the heating elements, but it goes continuously for up to 40 min.

The washer uses 49 kWh per 100 washes so it clearly cannot use full power for more than about 10 minutes per wash.

It does depend on:

• How frequently they are on for together
• Whether the tumble dryer is often used on high heat settings
• How near the standard limits of temperature rise the plugs and socket-outlet gets
• How much ventilation there is around the socket-outlet.

As examples:

• I've seen more problems with a twin trailing socket-outlet (but that's obvious, as there are likely more twin fixed sockets on a 2.5 sq mm run or ring rather than a 1.5 sq mm spur, so potentially the cable is hotter in the first place).
• I've seen more problems with double socket-outlets in certain kinds of plastic backbox in kitchen cupboards, than I have in or on brick walls.
• I've seen more problems with double socket-outlets where there's likely insulation in the walls (higher cable temperature).

Just because this arrangement of your particular model of washing machine & tumble dryer (and the respective usage cycle) is OK in one installation, does not mean it's OK in every installation. 

gkenyon: 
Just because this arrangement of your particular model of washing machine & tumble dryer (and the respective usage cycle) is OK in one installation, does not mean it's OK in every installation. 

I didn't say that, but equally well, not every “overloaded” twin socket will be damaged.

So Mr and Mrs O. Person move in and the removal man plonks the washing machine in the utility room next to the water supply, drain and socket outlet. The drier is placed next to it (it too needs a drain for the condensate). Naturally both get plugged into the one double socket.

Of course, the sinner is the sparks who should have installed two single socket outlets, either on their own back-boxes, or on a twin one.

Or was he (she)? Perhaps originally the drier was situated elsewhere?

Chris Pearson: 
I didn't say that, but equally well, not every “overloaded” twin socket will be damaged.

So Mr and Mrs O. Person move in and the removal man plonks the washing machine in the utility room next to the water supply, drain and socket outlet. The drier is placed next to it (it too needs a drain for the condensate). Naturally both get plugged into the one double socket.

Of course, the sinner is the sparks who should have installed two single socket outlets, either on their own back-boxes, or on a twin one.

Or was he (she)? Perhaps originally the drier was situated elsewhere?

Interesting nuance … do you always design every aspect of your electrical installations for the unexpected in the same way?

So, I'm not trying to be purposefully awkward, but the issue is that we have case law that leads us to the point that we need to account for the “next person off the Clapham Omnibus” and also that someone carrying out DIY has to exercise the same “skill and care" as a competent tradesperson doing the same job.

The person on the Clapham omnibus is, quite reasonably, likely to assume that if he has two thirteen amp sockets then he can plug in two thirteen amp plugs whatever is connected to them.   

The face plate of a double socket does not carry any warning about maximum load.  I assume that double sockets, rather than twin singles are fitted to save a pound

My tumble drier is a condensing one and uses 1.3kw some of the time. The washing machine heater is 2kw, the motor not a lot except when spinning. I don't understand this worry about the socket rating, just what are people expecting to overheat in a few minutes, and how is this different from a single socket?

Reasonable questions I think, but from above one would expect a fire every few minutes somewhere in the country. It is very rarely a problem and is usually due to something other than a socket in good condition. Poor quality plugs and fuses are a more common problem.

From the standards point of view, I do not see why a double socket is not rated at 26A, as it should be. The only reason can be that the connecting copper to each socket is perhaps too small, but this is unlikely and fixed for a trivial cost, or this is some kind of compatibility with other standards problem, but it is pretty much a UK and ex provinces standard anyway. It cannot be beyond the wit of man to change the rating to a sensible value? In fact I suspect that the 13A marking on some sockets is an error by a non-engineer in reading the specification, it is simply a single socket rating. Many manufacturers quote 20A in literature, again properly from the approval specification.

I also fail to see why we endlessly have questions about “current ratings” of everything when there are very few problems observed. OK, some think that BS7671 numbers apply in unintended ways, that time is not part of diversity understanding, and that fires can be started at 100 degrees, and are so risk-averse that they cannot see beyond their own reality. All of this comes from a completely broken education system, please learn some basics, it will make you much happier!

davezawadi (David Stone): 
 

I don't understand this worry about the socket rating, just what are people expecting to overheat in a few minutes, and how is this different from a single socket?

Most folks will not appreciate the ratings or be concerned about what's plugged into a double socket or even a triple adaptor. A plug is a plug to be used; is a duty of care required?. There is a problem with the standards in that this is a situation that's allowed. Is it a risk situation …………. Yes!. 

Much ado about nothing?. Has there been resultant incidents of misuse? - probably unknown, they would be unreported unless there was a report at the inquest of a fatality or fire etc. 

Jaymack   

gkenyon: 
Interesting nuance … do you always design every aspect of your electrical installations for the unexpected in the same way?

________

 

So, I'm not trying to be purposefully awkward, but the issue is that we have case law that leads us to the point that we need to account for the “next person off the Clapham Omnibus” and also that someone carrying out DIY has to exercise the same “skill and care" as a competent tradesperson doing the same job.

Graham, what is the case law please?

The law looks at foreseeability. I would suggest that plugging 2 x 13 A appliances into a 13 A socket is entirely foreseeable. The duty of care rests with the designer/installer/inspector, perhaps jointly and severally if not one and the same. If a house catches fire due to an overloaded double socket, causation seems be straightforward.

So there we have it - an electrician might be negligent in installing double sockets anywhere that two high-current appliances may be plugged in.

But we also have to consider the standard of care (Bolam). Would a reasonable body of competent electricians install double sockets?

If there is case-law on this specific point, it would be interesting to read it.

(Incidentally, I took the no. 49 Omnibus to Clapham 8 days ago. All of the passengers looked very ordinary.)

You probably got on that bus on the wrong day !

You are fortunate. I've seen, sadly, cases of washing machine and tumble dryer connected like this, where plugs and socket-outlets (and sometimes both together) have been damaged by overheating in as little as a year. Various manufacturers' products.

I had the unfortunate experience of working in social housing repairs for 2 years, and tumble dryer sockets burnt out were a semi-regular occurence. There was also the occasional washing machine too, but it was mostly tumble dryers on their own single socket. I put it down as poor quality factory fitted plug tops. The socket outlets were usually unswitched single sockets, and, mostly, modern, in being less than 10 years old. There was usually no burns at the cable connections, so it would have been the socket to plug interface causing the excess heat.