On 25/01/2021 18:28, NY wrote:
"Tim Streater" wrote in message
...
I thought their "****ty two-pin sockets" were rated at more than 5 A.
I know that high-power devices like tumble-driers and washing
machines (on presumably electric fires) tend to be hard-wired in 220
V (like our cookers are) but portable devices like hair drivers and
vacuum cleaners can be powered from a 2-pin power socket, so those
sockets must be rated for more than 550 W (110 V, 5A).

Ah, https://en.wikipedia.org/wiki/NEMA_connector says that 2-pin NEMA
(US) mains plugs are rated at 15 A.

They may be rated at 15A but the fire danger is still real enough. Partly
because the current is twice as high as we'd have it (so four times the
heating effect in the plug/socket) but also because their plugs are
unbelievably flimsy. Describing them as "****ty" is just me being polite.

Are you saying that a plug and a socket that are stated as being rated
at 15 A can't really be used for that current because of the risk of
overheating? If they overheat, doesn't that mean (by definition) that
they *aren't* rated at 15 A?

And in fact you were even concerned that passing *5* A through the plug
and socket might cause overheating problems. So what *is* the maximum
safe current that does not cause overheating? Even less than 5 A?

It will depend a lot on how well the pins are in good contact with the
socket. US home wiring runs rather warm by our standards. They have a
lot of house fires caused by trailing leads overheating by comparison.

I think in fact the problem is that those thin pins, and the fairly
small contact area between pin and socket, aren't *really* rated at 15 A
even though it stated that they are. So it's the rating that is wrong.

The rating is sort of right for a nice new one with no oxidation and
fresh clean spring contacts. It goes downhill quickly from there.

Here in the UK, if the plug is rated for 13A, that means it is safe to
run a 3-bar electric fire (3 kW, which is 12.5 A at 240 V) through that
plug and socket without it overheating to dangerous levels (melting of
insulation) no matter how long it is left running. Presumably there is
an equivalent real-world figure for US 2- or 3-pin plugs - and it may
well not be as high as the stated 15 A!

I have seen UK 13A sockets melted by the use of a 3kW fan heater load on
a cold day when it never really got up to temperature at all. Nothing
wrong inside the plug some corrosion from damp in the wall socket.

2.4kW aka 10A is now the recommended maximum load for UK nominally 13A
plugs. They do run very hot just from the fuse alone at 13A.

US and continental plugs don't have the fuse self heating problem to
contend with which gives them a bit more margin to dissipate waste heat
from the connection between plug and socket.

--
Regards,
Martin Brown