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Old 07-02-2019, 05:25 PM   #1
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Default Ground fault detection system

I am trying to trace out a ground fault in an industrial facility. We have a 3 light detection on a 600v system. L3 is out and L1and L2 are at full brightness. At approximately 45 minute intervals the lights switch and L2 is out leaving L1 and L3 at full brightness for approximately 10 minutes then it switches back. Any tips on where to start looking? We have tried shutting off everything on that mcc except the office and boiler (because we are not allowed to shut them off) to see if the lights change but no luck so far.
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Old 07-02-2019, 06:56 PM   #2
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You should go into the boiler house and talk to the operators and ask what they have that automatically cycles off at 45 min. intervals then on at 10 min. intervals. Operations can be a wealth of info if you know how to decipher what they are telling you.
Alternately, go in the boiler house and watch and listen for the on and off of machinery.
It sounds as though you have two separate ground faults.
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Old 07-02-2019, 10:40 PM   #3
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Well, you narrowed it down to the boiler, or the office. Unless they have big office electronics, or a large Air Cond. load, it's probably the boiler. Next step is to schedule a shutdown, and crack out the megger. As far as the shutdown goes, give the big wigs a choice, either go with a scheduled one, or go with an unscheduled one. The unscheduled one will probably cost way more in lost production, damaged switch-gear, and possible fie. Might even get a near miss with the later. Is this a high impedance grounded system?
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Old 07-03-2019, 12:06 AM   #4
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Quote:
Originally Posted by Tabersnake View Post
I am trying to trace out a ground fault in an industrial facility. We have a 3 light detection on a 600v system. L3 is out and L1and L2 are at full brightness. At approximately 45 minute intervals the lights switch and L2 is out leaving L1 and L3 at full brightness for approximately 10 minutes then it switches back. Any tips on where to start looking? We have tried shutting off everything on that mcc except the office and boiler (because we are not allowed to shut them off) to see if the lights change but no luck so far.
Talk to the boiler operators to see what they are cycling the load either large arse fan blower or water circulation pump or couple other items.

You can tell the boiler operator they can schedule a shut down or bank it ( tempory turn off burner for few minuites ) then you can able check the ground fault situation.

sometime you may get lucky with ground fault detection searching due sometime with ground fault detection you can read the ampmeter if you see a unbalanced current then you may hit a jackpot there.

ditto with office side just try to talk to them to shut it down over the weekend when it running bare bone setting.

Which type of ground system you are running ungrounded delta or limited delta ground system ?.
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Old 07-03-2019, 12:24 AM   #5
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At the plant we had built in thumpers and we could take a ground locating ammeter and 9 out of 10 times we could find the ground without turning anything off.
This is the exact equipment we had. We had the STB 50107-G-08 ground fault locater.



LC
https://www.eaton.com/us/en-us/catal...grounding.html

https://www.stbinc.net/ground-fault-detectors.html
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Old 07-03-2019, 01:03 AM   #6
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Ask the power plant (stationary) engineer how often the condensate pump(s) and make up water pumps cycle. I found one in a compressor motor once that too forever to find when I was a power plant mechanic (my first trade- well before I ever was into electrical).

Keep us posted.
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Old 07-03-2019, 05:07 AM   #7
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Do you have motor controls with forward and reverse that reverse by swapping those two phases? That's the only thing I could think of that would make the ground fault alternate.

If the ground fault is in the motor or the forward-reverse switch, or the wiring between, it will switch phases when that switch operates. (On the yellow or blue in the picture below, between the motor and the switch.)
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Old 07-03-2019, 05:58 AM   #8
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Do you have motor controls with forward and reverse that reverse by swapping those two phases? That's the only thing I could think of that would make the ground fault alternate.

If the ground fault is in the motor or the forward-reverse switch, or the wiring between, it will switch phases when that switch operates. (On the yellow or blue in the picture below, between the motor and the switch.)
Splatz could very well be onto something there, I'd for sure look at any reversing starters.
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Old 07-03-2019, 07:18 AM   #9
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I'd start looking in the bathroom. That's the first place I go on all my jobs. 45 minutes sounds about right.
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Old 07-18-2019, 07:02 PM   #10
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Check your motors if L3 is flip flopping it is a 600 vac problem which in my experience I always find wires shorted or it led to a motor
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Old 07-18-2019, 07:04 PM   #11
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It is not in your control voltage unless your control voltage is 600 vac
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Old 07-19-2019, 01:57 AM   #12
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Hey everyone. Today I got the ok to shut down the office @ 4:30 after everyone was gone for the night. I started in the mechanical room in the office by switching off all the panels so I can shut down the disconnect on the feeder from the plant. Once it was all off all three lights were on again! I traced the ground Fault to the HVAC and it was the compressors on the AC. There were two and we think it would switch between compressors to give the other a chance to cool down.

Thanks for all your help everyone it is really appreciated.
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Old 07-19-2019, 06:27 AM   #13
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Quote:
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Hey everyone. Today I got the ok to shut down the office @ 4:30 after everyone was gone for the night. I started in the mechanical room in the office by switching off all the panels so I can shut down the disconnect on the feeder from the plant. Once it was all off all three lights were on again! I traced the ground Fault to the HVAC and it was the compressors on the AC. There were two and we think it would switch between compressors to give the other a chance to cool down.

Thanks for all your help everyone it is really appreciated.
Thanks for taking time to report back and tell us what the issue was and how you found it. It really helps us all to be better at our trade.
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