Stray Voltage with a ground fault

[Coyote]

Hello, we recently had a ground fault on a 480 3 ph ungrounded delta system. As you know that means that one phase (the grounded one) will read zero when measured to ground. But what we found while looking for the ground has me confused. There is and old abandoned 15"chase with three pipes in it none are conduits and they are cut of at both ends it is about 70 ft long buried 4 ft in the ground. It was discovered that the chase and all of the pipes when measured to either the earth or to building steel or piping that we recorded 240 volts. After the fault was cleared the pipe chase also cleared of any voltage. There are no underground conduits in the vicinity of the chase. Anyone have any thoughts on how this pipe chase became energized?:?

 

[GoldDigger]

Hello, we recently had a ground fault on a 480 3 ph ungrounded delta system. As you know that means that one phase (the grounded one) will read zero when measured to ground. But what we found while looking for the ground has me confused. There is and old abandoned 15"chase with three pipes in it none are conduits and they are cut of at both ends it is about 70 ft long buried 4 ft in the ground. It was discovered that the chase and all of the pipes when measured to either the earth or to building steel or piping that we recorded 240 volts. After the fault was cleared the pipe chase also cleared of any voltage. There are no underground conduits in the vicinity of the chase. Anyone have any thoughts on how this pipe chase became energized?:?

If you were checking the voltage using a high impedance meter, then you could be looking entirely at stray capacitively coupled voltage.
If, for example, the chase contained three phase wires from the ungrounded system, with no load connected at the far end, the capacitive voltage would be near zero when the three phase wires were roughly equal voltages from ground.
But when one corner of the delta gets grounded the average voltage on the three wires will no longer be zero. Probably close to 240V.

On the other hand, if the voltage was still there with a low impedance meter and maybe even with the chase connected to a ground electrode, then you have a hard connection somewhere. Probably to a derived neutral point from the ungrounded delta. With the delta free floating the neutral will be at or near ground. With the delta unbalanced the neutral would be at a high voltage and would be able to deliver possible substantial current.