Possible problem with Cutler Hammer Magnetic Starter

[mjr6550]

This starter is an old one-about 1958. It is on a Gorton P2-3 pantograph milling machine that I recently acquired. It is controlled by momentary start/stop switches. The machine is 240-volt 3-phase with a 1/2 hp motor. I am operating on a static phase converter and have only used it a few times.

The control circuit is 120 volts supplied by a 0.15 kVA transformer in the electrical enclosure with the magnetic starter. The control circuit has a 10 amp cartridge fuse.

Now to the possible problem. I started the machine over the weekend and the contactor immediately tripped out. I tried the reset button by no help. I took apart the reset button and removed the heaters to look for problems. They seemed fine, as does the contacts and wiring. I realized then that the fuse must have blown. No continuity through the fuse. I don't have a spare, so I ordered a few. My only thought is that I release the tension on the belts when the machine sits unused and I tightened them (maybe too much) before I tried to use it. Could that have caused the current draw to be too high? And, since this is a control circuit fuse, would that be affected by a high current draw?

 

[deltap]

Immediate trip points to an open safety or a short circuit. Heaters should take a short time to trip overload. Overload should not affect control circuit fuse. You could run the control circuit without the main power on to see if the problem is in the control circuit. You may need to power the control circuit with an extension cord when the main fuses are removed. First check all wiring for tightness and check all connections against wiring diagram. If control circuit fuse is inexpensive, replace and try again. It may just be a bad fuse.

 

[rons]

Fuse current rating and delay? Slow blow.