On May 7, 7:05 pm, Ignoramus23720 ignoramus23...@NOSPAM.
23720.invalid wrote:

I believe that this arrangement fully satisfies the rule that a
mechanical interlock device should prevent both sources of power from
coming in contact.

Any comments?

Yeah, I don't think an inspector would go for it. The inspector would
say "but if someone had the other key..." and you'd say "but it's in
the safe" and the inspector would say "but if someone had the other
key..." and out would come the [REJECTED] stamp.

That kind of stuff, the safety is in physical impossibility of linking
sources, not the reliance on a meat puppet to do the right thing and
not throw both switches at once.

In a restricted industrial setting, there can be different rules.
Residential is another matter...

DJ