Re: Plant grounding grid
Originally posted by charlie:
It sounds to me like you have a lot of neutrals that are re-grounded past the service equipment.
This would be my guess.
Recomendations:
1. Get a one-line diagram of the plant.
2. Ask where this 200A was measured.
3. Find another electrician to talk to. It may take a while to find a knowledgable one. Age and time on the job do not necessarily equal excellent understanding.
4. Don't discount anything you hear. If it doesn't sound right, it could still be true, just one of the two conversing doesn't under the physics.
5. The stuff you are relating doesn't make much sense to me. You are showing a lot of promise questioning it.
Just an aside, current on the grounding conductor is not necessarily dangereous. One case I just worked had about 25A on the grounding conductor. Code violation - oh yeah. Did we fix it - oh yeah. This particular facility has its own generation - a 350KW, 480V, 3 ph, 4wire. Generator has a 500A Main and the gen is grounded and bonded at the main. From there, a 3C-750kcmil with #2 bare, MC cable runs 600 feet to a switchgear room. The facility was changed significantly 6 years ago. The switchgear room was existing and set up for other generation. It is 480V, 3ph, 4 wire, solidly gorunded. There are 277V loads.
One of the electricians noticed the code violation. So I got out there with a clamp-on and there was 25A on the #2 bare. I couldn't tell how much of that was due to differences between the ground potentials at the two ends, and how much was due to the unbalance in the 277V loads. 25A doesn't seen like much, but it was about 8% of the normal load current.
I couldn't find any dangereous voltages hanging around on exposed metal or at the ends of the grounding conductor.
The point: What it is being measured and where is being measured, has a lot to do with if an objectionable ground current is an immediate danger.
(edited: to remove my comment concerning the person telling our member this stuff)
carl