Line Side Breaker Self Welded

[Jraef]

View attachment 19130

I figured I show a trimmed out schematic of the setup. Please don't judge this on me. I'm still thinking this has something to do with the relays on the 480VAC side

Electrically and logically, there is nothing wrong with that schematic. It's just poor practice to not have a mechanical interlock between the contactors for the reason I stated earlier, and legally if that reversing starter was not built as a factory assembled and listed unit, the HMCP is a code violation.

The simple fix by the way, since the breaker failed anyway, is to just replace it with a Thermal-Mag circuit breaker. An HMCP is not some sort of special magical breaker designed for motor loads any more, it's simply a Thermal-Mag breaker without the thermal trip elements, and where the mag trip is adjustable. There are now lots and lots of T-M breakers available that have adjustable mag trips, and the adjustment ranges, on something this size, will be exactly the same as an MCP. The only reason mfrs use them is because in volume, they save the $6 added manufacturing cost of the thermal trips elements inside. But I also strongly suggest replacing those contactors with a matched pair that has a mechanical interlock between them. The control circuit can remain exactly the same.

 

[kwired]

View attachment 19130

I figured I show a trimmed out schematic of the setup. Please don't judge this on me. I'm still thinking this has something to do with the relays on the 480VAC side

If no mechanical interlock, a forward contact could "weld itself closed" holding in forward contactor, then when a reverse command is given closes reverse contactor into a line to line fault. Electrical interlock allowed the reverse command because the controls were in an "off" state.