On 14/11/2020 19:15, williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?

Probably as others have said the switch can't cope with the high inrush
current at switch on and fuses the contacts.

The act of taking it out may be enough to free the spot welded contacts
so that when you later test it on the bench it is no fault found.

FWIW my suggestion would be to use a mains toggle switch rated for 20A
and see if it lasts any longer- a 20A rated DPDT with the contacts used
in parallel might be your best bet as a more robust solution.

If that still fails then a mains relay to switch the load would be my
next suggestion. BTW Rapid are usually cheaper than RS.

--
Regards,
Martin Brown