I am currently working in Afghanistan doing construction jobs for the US Military. We just finished a project that included a small office building, 120/208V 400 A MDP, and 125 KVA generator set up. As we are going through our final inspection, the inspector decides to throw his amprobe on the equipment ground going from the MDP to the generator. He got a reading of 5.9A, needless to say he won't sign off the building until it is gone. So I began going through the system trying to find where this was coming from. The ground going between the subpanel inside the building and the MDP was reading 0 amps, all bonding wires and wires going to ground rods also read 0 amps. Only this one section of wire was coming back with a reading of any amperage. The nuetral and ground are bonded inside the alternator of the generator. And my system has an Ohm reading of less than 5 ohms, so I know the grounding system is sufficient. Now here is the kicker, remember how I said there is no amp reading on the ground wire from the subpanel inside the building to the MDP, only the ground from MDP to generator.......when you put your amprobe on that ground, and you turn off all the lights in the building.....it goes away completely. 0.0 amps! The building is using lithonia T-8 high efficiency electronic balast lights from the states! Can anyone shed some info on this???
Unexplained Amperage
- Thread starter Sean_Carb
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ptonsparky
Tom
- Occupation
- EC - retired
Are the neutral & ground bonded again at the MDP?
brian john
Senior Member
- Location
- Leesburg, VA
1. Perform a zero sequence reading at the MDP
2. Do a zero sequence reading at the generator.
3. Turn off the light circuits one at a time, you most likely have a grounded neutral
at the MDP or in a branch circuit.
4. Turn off the system and turn off the CB's, isolate all the branch circuit neutrals and the
feeder to the generator, megger all of these conductors and locate the "short".
5. Check the neutral bus in the MDP for a ground connection
2. Do a zero sequence reading at the generator.
3. Turn off the light circuits one at a time, you most likely have a grounded neutral
at the MDP or in a branch circuit.
4. Turn off the system and turn off the CB's, isolate all the branch circuit neutrals and the
feeder to the generator, megger all of these conductors and locate the "short".
5. Check the neutral bus in the MDP for a ground connection
brian john
Senior Member
- Location
- Leesburg, VA
I should add there is no unexplained amperage just un-located sources of the current.
No, only in the alternator of the generator
brian john
Senior Member
- Location
- Leesburg, VA
How do you know this?
ptonsparky
Tom
- Occupation
- EC - retired
Refer to post #3.
brian john
Senior Member
- Location
- Leesburg, VA
Ahhhhhh, but did you test it? and all down stream neutrals.
brian john
Senior Member
- Location
- Leesburg, VA
No follow up on this issue?
brian john
Senior Member
- Location
- Leesburg, VA
I have asked this before (see previous post) but what was the issue.
I like to know what was wrong and how this was resolved. I think this forum deserves that much from posters asking questions and getting several avenues to check.
If we are wrong shouldn't we be told the solution to add to our knowledge base.
I know many posters may be real busy and getting back to post may be a PIA, but heck it only takes a few minutes to say the answer to my problem was XXXXXXXXXXXXXXX.
I like to know what was wrong and how this was resolved. I think this forum deserves that much from posters asking questions and getting several avenues to check.
If we are wrong shouldn't we be told the solution to add to our knowledge base.
I know many posters may be real busy and getting back to post may be a PIA, but heck it only takes a few minutes to say the answer to my problem was XXXXXXXXXXXXXXX.
ceb58
Senior Member
- Location
- Raeford, NC
Well said, Brian
With problems such as this, I usually attribute the solution to one which the poster adamantly stated, swore, or otherwise asserted as not being the problem :roll:
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