In article ,
Harry Bloomfield wrote:
Chris J Dixon formulated the question :
The potential hazard is that if the main contacts on one of the
contactors weld closed, then the system closes another contactor,
it thus creates a potential phase-phase connection.

If the contactor has auxiliary contacts, so long as their state
mirrors the main contacts if they are welded, then the safety
interlocking can be electrical.

Exactly! I would also want to provide some mechanical interlocking too,
to be certain it never could happen. I have come across mechanical
interlocking on star/delta motor starter systems, so I know it can be
done.

I was brought up on Castek Keys

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from KT24 in Surrey, England