Did I forget to mention I was dealing with DC, My bad. DC coils on AC do tend to chatter, so they have a shunt ring in the armature to square up the hysteresis loop. I think Mike hit the nail on the head, high wattage for bigger springs needed to move the armature fast at opening, but, couldn't the coil with the large spring be made of more turns of smaller wire, enough so as to pull the moving piece in any way, or would that create large counter EMF and slow the speed of the moving piece, or would that just move the half way there and not close the circuit? - - - Strong Spring, more wattage, more heat, smaller duty cycle or larger case for heat dissipation.
Ron, were they trying to heat the armature of a 3 phase motor while running of before running it, and I would guess this is a Y connected motor. I've applied dc to 3 phase motors to brake the rotor, rolling cranes, 12VDC on a 208/240 VAC motor creates a lot of drag, but is was interlocked for one or the other.