AC power on front panels
ard at p850ug1.demon.co.uk
Tue Jan 17 14:35:20 CST 2006
> Thanks for that remark, Pete!
> I did not want to go into "pedantic" mode, but I was indeed
> thinking about the capacitors in the EMI filter, but thought
> that chances are very slim that they fail. But they can!
The problem is not that they might go dead shorted. That would trip the
breaker or blow the fuse or whatever. The problem is that you get a leak
somewhere that draws significant current (say around 10A). That won't
blow the fuse, but that amount of power disipated in a small space will
get things very hot. Maybe even start a fire.
Not the same thing (because it's after the contactor), but I've had the
blower fan in an RK05 catch fire. The insulation on the windings broke
down, flames and smoke came out of the end of the motor, but the fuse
didn't fail. If I'd not been looking at the system it could have been nasty.
> Once in ten years is good, except if it's *your* filter that
> fails :-)
> The caps in the EMI filter have a very small leakage current,
> so if you are 'energy-concious' pulling the plug is truely
> the only option.
That shouldn't be as bad as you think. Your electricity meter records
true power (not apparent power), it will ignore the purely reactive
component of the current. OK, the current will not be purely reactive (if
only because of the seires resistance of the wires, etc), but the
in-phase component will be small.
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