PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
I had a service call today at a farm for a problem in a remote structure (approx. 400' run from main disconnect through house and garage) fed by a 12-2 UF which feeds a skeet thrower and plug-in fan via a few receptacles. The customer reported getting shocked from the metal boxes and EMT run between them. Another electrician had checked it out and removed some questionable wiring in the structure, but hadn't been able to eliminate the voltage on the ground.
When I arrived, the homeowner was not around so I started out at the "bunker" where the skeet thrower is located. I drove about 24" of #2 CU for a ground reference and two meters were showing me about 10V between the UF ground and the reference ground, and about the same between the N and ref. G, with both showing 15V peaks. I then found the other end of the UF in a garage and started checking splices to see if I could find a bad neutral or N to G short. I found one GFI recept on the same circuit with a short between N and G and fixed that. I still had the 10V at the structure, so I checked at the main disconnect. There I found a loose N lug (SquareD 200A disco, lugs are screwed into a plate - crappy design!). Fixed that, still had voltage from N and G in the skeet bunker.
At this point I decided to check if the problem existed at the main disconnect as well (up to this point I was under the impression from what the customer had reported that the problem only affected the skeet bunker). I moved my reference G to the main disco and got some strange readings:
From N to ref. G - 1.4V-9.1V
From either leg to ref. G - approx. 5 volts higher reading than from legs to N; ex. 122V to N, 127V to ref. G
The higher voltage from G and N to ref. G were intermittent with low readings at the disco about 1.4V and in the skeet bunker about 2.9V, which I suspect is partly induced voltage due to the long run.
The customer arrived home about 3 hours into my being there. An interview with him revealed that in the past, they had experienced a similar problem in the basement with the wash sink and an electrician had checked it out, recrimped the neutral connections at the service head, checked the connections in the meter socket and declared a clean bill-of-health in the house, at which point that electrician called in the POCO, who the homeowner thinks installed a ground rod at the nearest pole where the transformer is mounted, checked N connections from transformer to the meter socket again and gave their blessing to the whole thing.
To me this smells like stray voltage on the neutral coming from the POCO's line which in my limited understanding would explain why I get higher voltage to the ref. G. Does that sound like a valid theory, or am I missing something important? I checked all the panels and ATS for a G to N bond, but it all looked fine. I don't have datalogging equipment so I couldn't check if there is a correlation between load and voltage from N to ref. G due to the intermittent aspect of the problem but the house was mostly empty, no central air and peak loads seemed to be limited to a refrigerator or two.
I'd be grateful for any ideas of what theories are likely and what to check to prove or disprove them.
Thanks!
When I arrived, the homeowner was not around so I started out at the "bunker" where the skeet thrower is located. I drove about 24" of #2 CU for a ground reference and two meters were showing me about 10V between the UF ground and the reference ground, and about the same between the N and ref. G, with both showing 15V peaks. I then found the other end of the UF in a garage and started checking splices to see if I could find a bad neutral or N to G short. I found one GFI recept on the same circuit with a short between N and G and fixed that. I still had the 10V at the structure, so I checked at the main disconnect. There I found a loose N lug (SquareD 200A disco, lugs are screwed into a plate - crappy design!). Fixed that, still had voltage from N and G in the skeet bunker.
At this point I decided to check if the problem existed at the main disconnect as well (up to this point I was under the impression from what the customer had reported that the problem only affected the skeet bunker). I moved my reference G to the main disco and got some strange readings:
From N to ref. G - 1.4V-9.1V
From either leg to ref. G - approx. 5 volts higher reading than from legs to N; ex. 122V to N, 127V to ref. G
The higher voltage from G and N to ref. G were intermittent with low readings at the disco about 1.4V and in the skeet bunker about 2.9V, which I suspect is partly induced voltage due to the long run.
The customer arrived home about 3 hours into my being there. An interview with him revealed that in the past, they had experienced a similar problem in the basement with the wash sink and an electrician had checked it out, recrimped the neutral connections at the service head, checked the connections in the meter socket and declared a clean bill-of-health in the house, at which point that electrician called in the POCO, who the homeowner thinks installed a ground rod at the nearest pole where the transformer is mounted, checked N connections from transformer to the meter socket again and gave their blessing to the whole thing.
To me this smells like stray voltage on the neutral coming from the POCO's line which in my limited understanding would explain why I get higher voltage to the ref. G. Does that sound like a valid theory, or am I missing something important? I checked all the panels and ATS for a G to N bond, but it all looked fine. I don't have datalogging equipment so I couldn't check if there is a correlation between load and voltage from N to ref. G due to the intermittent aspect of the problem but the house was mostly empty, no central air and peak loads seemed to be limited to a refrigerator or two.
I'd be grateful for any ideas of what theories are likely and what to check to prove or disprove them.
Thanks!