VFD - earth ground fault

[Switcher]

Hello all,
We have a friend in the air conditioning business that recently installed a few rooftop cooling only carrier units on a school. The units are tripping in the VFD drive on a earth ground fault. The electrican that wired the school swears the grounding system is up to code. I haven't looked at the system yet. The VFD in the AC units is a ABB drive and the president of ABB says there is not another drive in the country that trips on this fault for any other reason than a faulty grounding system. The roof units are on the 2nd floor, 200 ft from the Main Distribution Panel on the
1st floor. We have a clamp on earth ground resistance meter to test electrode resistance and were planning on running a temporary wire from the AC unit to the MDP to test the resistance on the permanent ground. Anyone got any other suggestions?

Thanks in advance guys,
Alan

 

[infinity]

I'm a little confused. What does "The units are tripping in the VFD drive on a earth ground fault" mean? If the units are showing a ground fault how is that a problem with the grounding system?

 

[weressl]

Hello all,
We have a friend in the air conditioning business that recently installed a few rooftop cooling only carrier units on a school. The units are tripping in the VFD drive on a earth ground fault. The electrican that wired the school swears the grounding system is up to code. I haven't looked at the system yet. The VFD in the AC units is a ABB drive and the president of ABB says there is not another drive in the country that trips on this fault for any other reason than a faulty grounding system. The roof units are on the 2nd floor, 200 ft from the Main Distribution Panel on the
1st floor. We have a clamp on earth ground resistance meter to test electrode resistance and were planning on running a temporary wire from the AC unit to the MDP to test the resistance on the permanent ground. Anyone got any other suggestions?

Thanks in advance guys,
Alan

Make sure that the system is not a resistance grounded system. In that case you would need to remove some filters, and ABB has a provision for that by removing some screws. ASD's like to have their own grounding wire bought along with the feeder and be solidly grounded both on the P and PE terminals. How long are your leads from the ASD to the motor? Are they one of the approved methods and length of wiring?