Current On The Equipment Grounding System

[steveng]

zog

zog

what type megger would you use? would a fluke 1587 be a good meter for this type of measurement?

 

[wirenut1980]

Why would a megger pick up this short and a multimeter would not? I understand there could be some leakage current, but to measure 9 amps total from 4 subpanels, you would think that would be a pretty measureable short that could be detected by a multimeter.

 

[brian john]

One would think so in this case, but I ALWAYS use a megger for testing for this work. I generally start at 100 VDC to avoid possibly damaging equipment.

My meggers lowest voltage is 10 VDC and runs to 5000 VDC (different meggers).

 

[Phil Devine]

We found several places in pull boxes and light fixtures where the neutral conductors were pinched under the box or ballast cover. Once we repaired the damage we got good readings between neutral and ground on the circuits that had low resistance previously with the megger.

We also are still having failure of the 20 ampere switches (arcing when opened and shooting sparks out) with different ballast manufaturers.

 

[George Stolz]

Thanks for the update, Phil, keep them coming. Updates help with people who search later on, to see what the problem was in your case.

 

[weressl]

I do not believe changing the ballasts was the only cause of your issues. This is a school, and I cannot imagine that 9 amps of current on the grounding conductors is acceptable.
You and your team should spend as much time as is necessary to locate this problem.

If that is not acceptable, I have seen where Brian John has in the past offered his services to people out of his normal work territory. Maybe he can help you.

Brian - hope you do not mind, but I think this issue needs an expert such as yourself to locate a potentially very dangerous situation in a school.

Switching power supplies, ASD's and even some ballast operating at high frequencies - one type power saving ballasts - could dramatically increase the harmonic content without true RMS current reading and knowing the harmonic content contribution the unusually high ground current may not be abnormal.

 

[Phil Devine]

The testing company tested for TDH and found it minimal, and identified the fact that the current on the ground was 60 HZ.

 

[lovetagolf]

Testing company

Testing company

I work for the testing company that was doing the work on this project and was out at the site for most of the testing. What was determibned to be the problem was the switches were not rated for the inrush that was being created by the ballasts. Pass and Legrand switches have a rating of 95 max, and we were measuring 170 amps when the lights were switched on. The solution was to chang eto a Leviton switch that was more able to handle the inrush of the ballasts and that seems to have corrected the problem. We also found that the building steel the ground was connected to was not connected the rest of the main buildings steel, or connected to a true path to ground. They ran a ground to the steel, and now there doesn't seem to be a problem there either.

 

[brian john]

While I have seen instances where metal to metal connections do not exist, but I fail to see how one can resolve current on the ground by interconnecting all metallic parts of a structure.

This ground current is not some mystical animal looking for some steel to run to earth. The ground current may be more difficult to measure due to multiple paths but from what you described it just did not go away.