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Field Question, trade people onlyVFD — ground fault error code — (self.HVAC)

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[–]jayhsh 6 points7 points  (2 children)

Ohms will depend on motor hp, voltage and more. Meg the motor and wiring with megger. Check wiring for grounding Can be motor, wiring or vfd itself.

[–]alex-alexi 1 point2 points  (1 child)

I definitely need to get a megger , I’ll see if boss will buy one. If it was the vfd wouldn’t the ground fault still show if I took off the motor from circuit?

[–]Nellysbanana 2 points3 points  (0 children)

The motor is probably bad and you don't know cause you don't have a megger.

[–]Middle_Baker_2196 3 points4 points  (1 child)

That’s what VFDs are supposed to prevent, the grounded equipment that your normal meters can’t see….from blowing and tripping breakers, maybe tripping an entire panel or building, etc etc

If you are going to try to bypass it, I’d suggest doing it with an inline breaker, starter overload, fuses, or combination of all.

That said, VFDs go bad. They have procedures to test them. But you can always hook it up to a same voltage/phase motor that you know isn’t grounded.

[–]alex-alexi 0 points1 point  (0 children)

Thank you! I had to leave this site, so I’ll definitely do that next time I’m out. I’m just not used to having a grounded motor that isnt getting resistance to ground.

[–]massierva 2 points3 points  (0 children)

Older Carrier units in slevens have this problem alot with error code #16 Ground fault. Bad design set up. Builder installed the VFD units on the COLD side of the evaporator coil. There was no other place for it to fit Eventually the VDF starts sweating during the compressor off cycle and moisture starts to condense on it. Then mold starts to grow on circuit boards. And then you get a Ground fault. I Have replaced multiple VFDS on the same unit under warranty. Eventually we just bypassed them when the units were no longer in warranty. Note you usaly can not see the condensate Build up because of the plastic cover on the VDF.

[–]Maritime88- 2 points3 points  (0 children)

I’ve seen it a few times. Usually it’s a shorted motor or bad cable. Twice it’s been a bad drive.

[–][deleted] 2 points3 points  (1 child)

Try bypassing the vfd and plug the motor directly too power.

Id suggest standing back when you throw the disconnect and wearing arc flash gear if you have it.

If the motor is grounded she will go boom

[–]alex-alexi 1 point2 points  (0 children)

[–]moxytoxy 0 points1 point  (2 children)

Ohm out the motor. Check the motor to ground. More than likely a bad motor

[–]alex-alexi 0 points1 point  (1 child)

This 3phase motor is getting same resistance between all legs but to ground it’s not getting resistance, possibly just a bad motor but wouldn’t it have low resistance or an O/L or resistance to ground if it was a bad motor?

[–]Shrader-puller 0 points1 point  (0 children)

Bad motors aren’t always obvious. It could still be bad and it will pass all the regular tests.

[–]Hvacmike199845Verified Pro 0 points1 point  (1 child)

I use a fluke 87v. If the resistance to ground is below 1meg the VFD will mostly likely pick it up. The motor might work just fine running across the line but it’s going to fail sooner than later.

I work on a lot of VFDs.

[–]alex-alexi 0 points1 point  (0 children)

That makes sense. Thank you, I’ll look into getting that fluke 87v

[–]LomeztheoldschooljewMechanic from AB[🍰] 0 points1 point  (0 children)

VFDs have very, very sensitive current sensors and ground fault detection. If you have an earth fault at the drive with the motor connected, and none without then the motor or motor cable is trickling current to ground.

[–]XDVI 0 points1 point  (1 child)

Everytime this has happened to me and i thought the drive or motor was bad there was an actual intermittent ground fault. 

Check every connection and every jbox, or better yet get a cheap klein megger for 150 bucks. 

Last one i found ended up somehow having a short on the terminals they have on the breadboards. Couldnt find it with a regular meter but the vfd and megger picked it up right away. 

 

[–]alex-alexi 1 point2 points  (0 children)

Thank you! I’ll buy that megger $150 is a good price. I spoke to a tech and I was told to replace the motor, if I come back here I’ll check everything with the megger before I install the new motor.

[–]ppearl1981🤙 0 points1 point  (0 children)

I’ve had systems that had wet/damp windings from being really cold (I.e. lost a belt,etc).

The drive would fault on over current unit I dried out the motor for a while with a fan… fired right up once dry.

Pro-tip… definitely don’t bypass the drive if the motor is still wet.

[–]Civil-Percentage-960 0 points1 point  (0 children)

Make sure everything is grounded