Chiller Starter Zero Sequence GFI

I have a 540 ton 480VAC 3 PH Y-D closed transistion starter fed from a Y solidly grounded transformer secondary.
The complaint is that the chiller may experience a ground fault trip on the first start-up after not running for a long period of time. The gfi is reset and the chiller starts and runs. This problem has been happening for years.

When I took a first look at the starter I found that there is a zero sequence (core balance) CT on the line side of the main mold case non automatic breaker. This main is fitted with a shunt trip operated by the GFI relay.

The issue that I want to get your opinion on is this:

The installing contractor ran the the phase conductors and the Ground conductor through the CT. There is no Neutral conductor.

I am thinking that the ground conductor is not to be running through the ct and could be causing the problem.


tremblay.robin (unclebob)
Exactly, no ground conductor should run through the CT.

Above is a snippet.

Did that fix the problem?

Keith - I have a feeling there is no op to provide feedback for this particular post on simpliengineering… just a clone of the eng-tips op.

I was going to add my two cents to the op (before I realized there was none) that having safety-ground wire through zero sequence CT causes bigger problems than just spurious trips, it means you are not protected for an actual fault from phase to case ground which will return through the ground wire and through the CT and not be detected.

Thanks EP. You’re right!

And I agree with your assessment too…