Was called out to a cooling tower main breaker tripped. Found that the motor contactors for the 480V 30 HP fan were arc welded closed. This is actually a two speed one winding type fan with interlocked contactors. It appeared that the low speed welded shut then the high speed pulled in and welded shut. Found the overload relays set on auto reset.
These are IEC style contactors and overloads, it appears that the overloads did in fact trip and then reset until the main breaker tripped. Some control wires that have nothing to do with the motor circuit run right next to the overload relay are browned from heat.
I have megged out the motor and found no problems.... yet... need to hook up new contactors then stand back.
I have ordered new parts and will set all overloads on manual reset. Just wondering if anyone here sets any sort of overload relay to auto reset.
Many thanks
