Tim Wescott writes:


There are bazillions of things that can go wrong inside of an electronic
device that'll make it 'stick on'. Unless your VFD has been
specifically engineered so that you can trust your life to its built-in
shutdown, use an external shutdown.

Better than my wording. except I'd say "external emergency shutdown"
to be explicit. No reason not to have other ones.

Here's another case: A mag-locked exit door, with an EXIT button
adjacent. Every code I have seen requires that to be a NC pushbutton, in
series with the lock. Push it, the lock has no power, period. You escape
the fire.

Another example of safety design: it's considered bad form to have a
microwave oven running with the door open. So it has two sets of door
switches that, if either opens, the oven is off.

PLUS, there's a third switch that CLOSES when the door is open. If
somehow, power IS still on, its contacts short out the power and smoke
something [fuse/breaker/etc.]

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433