Voltage readings at detached garage

[kwired]

In his first post the OP says he is dealing with cable feeding a 100 amp panel in a detached garage. In another post he says it's three wires. If the three are as you say, then there should only be 120 in the garage, no 240, and we don't know that for sure.

Has he confirmed it is a three wire cable straight from house panel to garage? Part of why I asked for more clarification of what is there. He said it is very old install - maybe at one time was a "chicago three way" setup and never had an EGC?

IMO we have not ruled out some possibilities that maybe never would have had an EGC to begin with.

May ultimately still end up replacing the wiring between the two buildings, but is nice to know what you have and not just guess what the problem may have been. I'd be ensuring I did/did not have continuity through all three conductors before assuming one of them is lost/disconnected, to do that you need to be positive you are not missing a junction box/splice point somewhere as well, or there may be more components of the circuit that need looked into.

 

[electricalist]

Id say there is no ground to the panel in the garage and the voltage to ground is from a conduit coming into the panel or a ground rod.
I think gfci s on every circuit would be a good start til you can get a true egc home.

 

[kwired]

Id say there is no ground to the panel in the garage and the voltage to ground is from a conduit coming into the panel or a ground rod.
I think gfci s on every circuit would be a good start til you can get a true egc home.

I kind of lean toward that assessment as well, pending some verification of where the three incoming conductors actually run to. If there is no EGC and there is no metallic paths back to the first structure - this allowed to have the grounded conductor bonded at the second structure under exceptions to 250.32(B)(1). And in older codes it was allowed to bond it anyway and is possible it just was not done.

 

[Smart $]

I kind of lean toward that assessment as well, pending some verification of where the three incoming conductors actually run to. If there is no EGC and there is no metallic paths back to the first structure - this allowed to have the grounded conductor bonded at the second structure under exceptions to 250.32(B)(1). And in older codes it was allowed to bond it anyway and is possible it just was not done.

Perhaps... but there is no viable explanation for the difference in measurements other than phantom voltage. The OP readings are claimed as 115V L-N, 26V L-G, and 26V N-G.

Draw a line 115 units long. At one end, draw a circle with radius of 26 units. Draw same size circle at other end. The circles represent all possible voltage vectors referenced to their respective ends. The circles do no intersect. Their has to be some physical manifestation to account at the least for the smallest gap between circles (63V).

 

[electricalist]

Maybe they intersect where the plumber ran a waterline to the gatage

 

[kwired]

Perhaps... but there is no viable explanation for the difference in measurements other than phantom voltage. The OP readings are claimed as 115V L-N, 26V L-G, and 26V N-G.

Draw a line 115 units long. At one end, draw a circle with radius of 26 units. Draw same size circle at other end. The circles represent all possible voltage vectors referenced to their respective ends. The circles do no intersect. Their has to be some physical manifestation to account at the least for the smallest gap between circles (63V).

We don't know what objects may be buried in the ground that can bring these circles closer together. I didn't go back and look very carefully, but did OP say how far away the garage is from the house, or what grounding electrodes are present?

 

[Smart $]

We don't know what objects may be buried in the ground that can bring these circles closer together. I didn't go back and look very carefully, but did OP say how far away the garage is from the house, or what grounding electrodes are present?

IIRC, he stated neither. A comprehensive description may be helpful.

The only thing that can explain the gap between circles in my mind is a same-line earth fault... that coincidentally raises the potential of the ground measurement reference point to 26 volts above neutral.

 

[electricalist]

In houses here the city water lines(copper) run from the alley and plumber often stub up water at the garage before going to the house as well as a closed loop for sprinklers. Its possible he has a gec at cold water running right beside the garage where a ground rod is trying to refrence it