Electronic components sources

If a HI-POT test is what I call a megger test (that's a high voltage earth leakage test) or flash test (high voltage breakdown test) then it must be done with the switch _on_ (and in certain cases with internal relays shorted out or otherwise operated). Otherwise you're just testing the bit of wire from the mains input to the switch. Odd. The UK regulations specifically suggest breaking both live and neutral (although live only is acceptable in many cases). And for 3 phase star, breaking all 3 phases and neutral. You can't have independant protective devices (like fuses) in both wires, in case the one in the neutral wire blows first and leaves the whole thing connected to the live side of the mains. But you can certainly have a double-pole circuit breaker that breaks both wires together. You cna even have trip coils in each wire, provided that overcurrent in either wire causes the breaker to break both (If you only have a single trip coil, it has to be in the live side. For 3 phase, it's recommended to have a trip coil in each phaae wire, but for delta connected 3 phase, you can have one in each of 2 of the phases, I believe). It's also strange that _every_ piece of quality electronic equipment I have here, from the likes of Tektronix, HP (that's _old_ HP, not the modern trash with that name on it!), DEC, etc, has double pole mains switching. It's also recomented in _every_ electornics construciton book I've looked at recently. Can you give me a good phusical explanation for this. The only one I can think of is if the switch fails so that the live side doesn't open any more then you'd have the equivalent of a single pole switch in the neutral side. You;d not notice that (the switch would still turn the device on and off), but it could be dangerous. But I have never seen that failure mode. No, the techincal term is 'electricians', at least over here ;-). Seriously, I've seen some terrible wiring done by so-called professional electricians, including a distribution panel on a workbench where alternate socket outlets had live/neutral swapped (!). -tony