Got a call today about some lights not working in a wood framed storage building, metal siding. There is an outside subpanel (main lug) fed with single phase, 2 hots, a nuetral, no ground, direct burial, 208/120v. Bonding screw is in place, no ground rods. Check voltage and get some weird readings like 200v A leg to nuetral, 0v B leg to nuetral. Turned off all breakers and put on 3 fluke meters A-N, B-N, A-B. Everything looks normal with both legs to nuetral at 120v and A-B at 208v. Turned on a breaker for one 8' HO, viewed the meters and got A-N 30v, B-N 178v, A-B 208v. So I'm thinking I am losing (or lost) the neutral feeding the panel. It is about 300' back to the building where it is tapped from, 100% under asphalt and concrete. Any suggestions as to anything else to check? Is the lack of grounding contributing to this? I'm thinking about trying to megger the N wire, we have a small handheld fluke megger that rarely sees any use.
Panel Problems
- Thread starter 347sparky
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Sounds like you have a broken neutral somewhere. Either at the connects of in the ground
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130110-2014 EST
Run a test lead from neutral or ground at the main panel to the shed and in your above test measure the voltage from the test lead to the neutral. Almost certainly it will show a large voltage (the voltage drop along the neutral). For a quick check just put a screwdriver in the ground near where you want to test the neutral voltage. If you only had a small offset in the neutral voltage, then the long test lead would be required.
Check for voltage drop at the termination of the neutral at the main panel with the one light load. But do not keep the high voltage on the light very long.
.
Run a test lead from neutral or ground at the main panel to the shed and in your above test measure the voltage from the test lead to the neutral. Almost certainly it will show a large voltage (the voltage drop along the neutral). For a quick check just put a screwdriver in the ground near where you want to test the neutral voltage. If you only had a small offset in the neutral voltage, then the long test lead would be required.
Check for voltage drop at the termination of the neutral at the main panel with the one light load. But do not keep the high voltage on the light very long.
.
ptonsparky
Tom
- Occupation
- EC - retired
I
Keep your hands off the side of that metal building. The kids in the house and the dog in the kennel. The voltage on the side of that building can become quite high. Bad neutral or poor connection someplace. It can usually be found even under asphalt.
Keep your hands off the side of that metal building. The kids in the house and the dog in the kennel. The voltage on the side of that building can become quite high. Bad neutral or poor connection someplace. It can usually be found even under asphalt.
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