A lot of installations using Carling type switches require/use a relay instead of directly switching the load.
The way most of these switches are configured almost always puts the internal on/off indicator LED directly across the load - like this:
switch1.JPG
This is fine for non-inductive loads, but when switching a relay there is a significant back EMF produced when the relay is de-energised.
This will put a large reverse voltage across the LED.
A LED's maximum reverse voltage is very difficult to obtain with any degree of certainty, but with the older types it is considerably greater than the more modern 'super-bright' ones which are generally speced very low (as low as 5V according to a lot of information). But they will all be far less than the peak back EMF which could be in the vicinity of 1,000 - 1,500V.
Does anyone know if any protection is provided for the LEDs within the switch (apart from the current limiting resistor)? I have not been able find any relevant information on the web.
Has anyone had LEDs fail when switching relays? Have you ever dismantled one of these switches?
It is a relatively simple matter to resolve the issue with a suitable diode across the relay like this below, but I'd like to know if it is really necessary.
switch2.JPG