Even if you leave that out, the sneaky b*ggers have opposable thumbs
and enough intelligence (or perhaps some kind of instinct) to operate
the plug on the power cord.
Well, you're definitely right on this one... These crane operators are
known to stick their hands into a 250 VDC panel from time to time.
This magnet is on a bridging crane (one in which the operator goes for
the ride). One time a maintenance employee looked up at the crane
overhead and saw the operator in front of an open electrical panel.
Soon later the maintenance dept. got a call that the crane was
inoperable. Apparently the operator wanted to set himself up with a
comfortable long break while the repair had to be done. Management put
an end to this by requiring the operator to sit in his crane cab
whether or not the crane was operable.
So, any design would have to consider attempts to defeat the system.
If the operator could just reset the clock by turning on and off the
power, that wouldn't be an acceptable design.
BTW, if anyone has a need for "vandal resistant screws" they are
available through McMaster Carr. I've seen many instances in a factory
where they are useful. Employees at the shop love to turn down the
volume on the speakers for the public address system. Then they can't
hear when they are called for a job. When the boss walks over to talk
to the worker in person, he just says, "What? I couldn't hear you
because the speaker is "not working". Vandal resistant screws would
make it difficult for personel to open the local call-boxes and
manually turn down the volume control.
Best regards,
Spehro Pefhany
http://www.speff.com