1.0 kva controltransformer blowing secondary fuse.

[mikewilliams63]

I have a 1.0 kva control transformer. The secondary common is grounded from the factory. Secondary voltage is 120. Periodically, I've had my control fuse blowing. It's a 15 Amp/250 volt fuse (factory sizing) Upon my arrival to the machine, I immediately unhooked my secondary ground because I needed to check for any shorts or grounds and I didn't want to read thru my transformer and get a false reading. I determined that I did not have any grounds or shorts so I replaced the fuse and applied power. My unit started and all looked great at 2.9 amps. I went to reattach my ground and immediately blew the fuse. I replaced the fuse again, I unhooked my ground and started my machine ....I checked the voltage from hot to ground and had 0 vac while the common side (ungrounded still) has 120 vac...how is this possible? Thanks.

 

[EC Dan]

How did you 'determine that you did not have any grounds of shorts'? It sure sounds like you have an existing ground fault somewhere in your unit, and adding the ground connection at the transformer completes the circuit and blows the fuse. Also explains why you have no voltage difference between hot and ground while running.

 

[retirede]

If the fuse is blown or removed, you won’t read to ground through the transformer. There was no reason to lift the ground.
I agree with Dan, you have a ground fault, perhaps intermittent, only occurring when something gets energized.

 

[petersonra]

Sure seems like a gf somewhere.

 

[tom baker]

I had a similar issue and installed a larger fuse. The cause was a failing solenoid coil, with the larger fuse the coil shorted out

 

[augie47]

I had a similar issue and installed a larger fuse. The cause was a failing solenoid coil, with the larger fuse the coil shorted out

That's the smoke test, correct ??
Increase fuse size until smoke leaks out

 

[retirede]

That's the smoke test, correct ??
Increase fuse size until smoke leaks out

As long as location of the smoke leak isn’t your transformer!

 

[tom baker]

That's the smoke test, correct ??
Increase fuse size until smoke leaks out

This was a pump control system in a vault. Hard to access