Washdown transfer pump, PowerFlex 525, 3hp, 480VAC. Motor sits outside on a pad with its own junction box. For three weeks now the first start of the morning trips F013 Ground Fault. Reset it, start again, runs clean all day. Next morning, same again.
We swapped the drive for the spare. Next morning the spare did it too. I pulled the motor lead lugs at the drive and went over them, tight, no green, nothing burnt.
Two drives, same fault, same time of day. A lad at our sister plant said these are known for being touchy on ground fault, so is there a way to back the detection off a bit? Feels oversensitive first thing and nothing else on that pad complains. Or is the first start of the morning telling me something about a motor that sits outside all night, because I'm out of ideas after two drives?
Don't make it less touchy, the drive's protecting itself and the motor. Why the morning is the question. Damp, I reckon. Damp nights, cold? Megger the motor and cable before the first start, then again after it's run an hour. Two readings, not one.
Ok, what voltage on the megger? We have a 1000V one in the shop, not sure that's the right setting for a motor. And yes, damp mornings. We're next to the river, fog most nights this time of year.
500V, motor leads off at the drive end. Lock the drive out first and wait for the bus to bleed, three minutes with the light out before you touch the terminals. Read at 6 in the morning cold, then after an hour of running. Discharge the leads to ground when you're done, that much cable holds the charge.
I'll bet under a megohm cold and a hundred plus warm. That's water in the junction box or the winding, the running heat drives it out, and the drive's right every morning. There's no drive setting for this. Open the junction box on the motor and look: flat gasket, missing drain plug, water in the bottom.
Meggered at 6am before anyone touched it: 0.4 megohm. After two hours running: 60 megohm.
Opened the junction box. Gasket flat as paper, no drain plug in the bottom hole, and a puddle in there. Photo attached. New gasket, drain plug fitted, dried it out with the heat gun. Will know tomorrow.
Water in the box. The drive was right every morning.
Two mornings clean now.
It was water sitting in the junction box overnight, insulation down to nothing cold and back up once the motor had run the damp out of it. A gasket and a drain plug, and nothing on the drive at all.
The drive I swapped out is sitting in the bad bin with a tag on it, it's fine, going back on the shelf. What I still don't get is why it only started three weeks ago, that gasket looked years old to me.
Thanks ed, dan.
Three weeks ago is when the fog started. Drive goes back on the shelf.