On 18/12/2015 19:43, Tim Watts wrote:
On 18/12/15 19:32, ARW wrote:

I would expect the cable could be at 40C at that load.

However if you suspect that the switch is getting hotter than the cable
then swap the switch [1] as it is only a few quid and see what happens.

[1] A Yorkshireman can spend other peoples money:-)


Thank you Adam. Did not think to check the cable. IIRC I used 10mm2 for
that one.

Thinking P=I^2 x R, even if the switch has a contact resistance of
0.01 Ohms, that, for I=40A, would be 1600 x 0.01 = 16W developed across
the contacts. In a fully plastic enclosure, I guess that is actually
quite a bit of heat. Could be reasonable I suppose...

Yeah - I'll get a new switch of the same make (for same terminal layout)
next time I'm up TLC in a week or two.

One other thing to think about is to uprate the switch to say a 60A,
that will give you more headroom between the actual current flow and the
maximum current rating of the switch, that hopefully would reduce I2R
losses across the switch and hence reduce the overheating effect?