According to daestrom :

"Chris Lewis" wrote in message
...
According to Mark Rand :
It's not a switch, it's an interlock. To be interfaced with the switch to
prevent it closing unless the interlock bar is retracted. It thus becomes
physically impossible to have both switches closed at once, since the
switch
must be opened in order to be able to extract the key and the key must be
in
the interlock in order to close the switch. Since there is only one key
available, only one switch can be closed at a time... even if they are a
mile
apart.

If the devices are installed properly, and _present_. How would
they be installed? Bolted to the panel face plate? What if the
plate has been removed?

Iggy's solution is far safer than the silly panels with switches linked
together. Specifically, it is fail safe.

Not quite. A large DPDT knife switch is failsafe.

Unless of course one blade comes loose from the handle and sticks in one
position while the other blade moves to the other position. Some folks
would notice that and probably do something about it, but a knife switch
isn't 'failsafe'.

Okay, okay. Sigh ;-)

Designing relay and control systems to be truly 'failsafe' is a whole
science unto its own. :-)

Being in computer security, there's no such thing as failsafe, it's
simply a matter of deciding how failsafe you want it compared to
how much you're willing to pay for it.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.