"James Sweet" wrote in message
news:iJvvd.4172$N%6.261@trnddc05...

| It isn't easy to mechanically interlock relays.

| Why would you need to though? Just use multipole, double throw relays and
| you can wire them together to do just about anything you want. I missed
the
| exact function of the original device though.

Hard experience has taught us that when a motor is operated both forward and
in reverse, it is best to make damn sure both contactors cannot close at the
same time no matter what. Thus the choice of a mechanical interlock system
so that even if the contacts weld closed on one side the other contactor
cannot close.

NM (Electrician)