The temperature is decided by the typical temperature budget of the cable feeding the socket, which if PVC insulated, would normally be 70 deg C.
Needless to say the cable does not immediately fail if that temperature is reached, however the lifetime of its insulation will start to reduce with overheating.
So you'd be happy with things inside your wall being at 70C?
More info here
You are falling into a common trap of conflating overload protection and fault protection, and also assuming that it falls to the circuit protective device to proved both for "everything".
In the case of a general purpose socket circuit, the protective device at the origin of the circuit needs to provide both fault and overload protection for the circuit as a whole, but not provide overload protection for each individual accessory, since that can be provided by other means.
The test regime for double sockets requires a long term loading test with a 20A load. This is a solid and sensible engineering practice that reflects a maximum load that will be "higher than reality". While you may think you can contrive ways to get larger loads onto a single socket than that, you will find it far harder to achieve in practice. (the fact that sockets are not melting all around the country every day indicates that the design has been very well proven in practice).
Some socket makers (MK for example) claim to test their double sockets with 26A of loading, however many will test only up to the level of that required by the BS since that is all that is required to put the product onto the market.
There is nothing stopping you using 20A circuits if you prefer, however in domestic environments they tent to prove far less flexible in high load areas like kitchens.
For definitions of "easy" that include really rather difficult. The vast majority of 13A loads that you can find to plug in, tend to be relatively short term in real world cases.
What not have a go at costing it and see? Over engineering things for a one off solution is sometimes acceptable. However for common items that will be deployed many hundreds of millions of times, a 20% increase in manufacturing price may well be "too much", especially as the current design has been proven to work so well and safely.
1.5mm is rated at 20A if clipped direct with no insulation touching it. It is rated at 10A when surrounded by insulation. Now most people have lighting cables and insulation in their loft.
Think about it - do you see the reason why it is used?
It's not just the cable that gets hot though. I don't want my flammable wall that warm.
I've seen a flex (for a fan) melt right through when it was against a radiator. I don't know what the water temperature was (old commercial installation), but it shows that the plastic couldn't handle about 100C or less.
It must be pretty common for someone to plug 2 of a dishwasher, washing = machine, and tumble dryer into a double socket, and quite likely to run = both at once. They've all got pretty powerful heaters in them.
I'd prefer just to have a double socket than can handle the same as two = single ones.
I can run a tumble dryer for an hour and a half, more if I have a lot of= washing to do after coming back from holiday for example. Same applies= to the washing machine and dishwasher.
But double sockets are pennies. It's not like we're talking about =A350= items here. They're nothing compared to the total cost of an installat= ion.
-- =
In the beginning the Universe was created. This has made a lot of peopl= e very angry and been widely regarded as a bad move.
Not on a FIVE amp circuit, no. You've still got double the rating required.
1) An unfused spur is restricted to a single accessory. That limits the maximum load to 26A. 2) 2.5mm^2 cable has a "clipped direct" rating of 27A - if the installation conditions are likely to reduce the current capacity of the cable to below 20A then the designer needs to change the design. 3) Cables are designed to get "hot". So long as they are kept under 70 degrees during normal operation, no harm will come to them. 4) as has been pointed out elsewhere, if you do manage to get an excessive long term load on the socket, it will typically fail long before the cable feeding it. 10A in its clipped direct rating in fact...
Well, on the down sides:
1) Material cost - £20 less profit per reel2) Time / Labour cost - probably another 50% installation time using heavier than required cable. That could easily be another day on a house rewire - so another man days lost productivity.
3) Maintainability reduction, circuits are now harder to extend and test in future (terminations take longer, and terminal space allows for fewer wires).The up side:
Can't think of any...
In some cases it will actually make it more likely. If you have to cram too many wires in undersized terminals there is a greater possibility that you will end up with a poor connection that overheats.
e:
Read up about diversity factor.
And for the houses with 10A lighting circuits?
I have read some powerfully dumb stuff in the past, but every now and then, scotty comes up with a new gem!
ote:
The total lighting load in my house is less than 150W (LEDs and CFLs) Just over half and amp? And I never have all the lights turned on. Why would anyone want 1.5mm2 cable these days?
So fit 1.0mm^2 then. It's the smallest you are allowed to use on a fixed install.
Stupid is as stupid does.
If you fit a decent cable that can handle 30A, it's protected by the CU = fuse and you can add more than one item to it.
Still twice the requirement for a 5A lighting circuit. We're overengine= ering lighting cables and underengineering sockets.....
I was thinking of someone just doing two jobs. Not someone doing it for= a living where he can use the cable up later on.
I was considering a small job - fitting a shower. As the cable is in th= e loft, the fitting time of the cable is nothing compared to actually fi= tting the shower itself.
It'll last forever as it's never run anywhere near full load. And the c= able was handy at the time, no time or fuel wasted going to buy the "cor= rect" type.
Either it fits in or it doesn't.
-- =
What did the elephant say to the naked man? How do you pick up anything with that?
I'm not into gambling.
Then you fit the 1.5mm wire. But this house does not have a 10A circuit.
Incase it gets physically broken?
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