ron said:
. . . and that many residential pole mounted transformers seem to only have one conductor from the primary side that goes from pole to pole, isn't the earth return used for many residential distribution systems? Is there commonly current returning on earth, essentially being considered stray?
The diagram he has is something that could happen in the worst of circumstances but is very unlikely to happen. All of the electric utilities that I am familiar with use single (primary) bushing transformers to serve residential customers. The transformer is fed from a single phase (
normally 15 kV class, not 5 kV as he shows) as shown in his diagram and the primary coil is normally connected to the inside of the tank where the external ground is attached. The tank is then attached to the pole ground (normally a #6 Cu. or equivalent) that goes to the ground rod. The secondary neutral has a grounding strap that goes from the center bushing to the tank to establish a grounding point for the neutral. The transformer legs and neutral are then connected to the secondary that feeds all of the customers that the transformer serves. The transformer legs are normally #2/0 Cu. or larger and the primary neutral is normally also the secondary neutral.
In order for Ronald Coleman's scenario to work, the grounding jumper must be removed and the grounding strap must be removed as well as the transformer secondary neutral connection to the primary neutral. I am not saying it can't happen, I am saying it is not likely to happen.
To address the question of stray current (the proper term by the way, not stray voltage). Consider that all (most) of the electric utility's MGN (multiple grounded neutral) are grounded at least four times per mile and at every equipment pole (transformers, capacitor banks, lightning arresters, etc.) Also, most electric utilities will put lightning arresters at switch locations and dead ends. Each of these locations will then be connecting the earth in
parallel with the earth back to the transformer that feeds the circuit. That transformer is in the substation and there will be some current return through the earth. That is why the equipotential plane is so important around swimming pools and agriculture milking parlors. :smile:
iwire said:
I was under the impression the NESC prohibits using the earth as a only return path.
Seems like touching the down wire to the electrode while standing on damp ground would be a bad time.
The NESC does permit the SWER but we do not use it and I know of no investor owned electric utility that does use it. It permits a single wire to be used for the primary and use the earth for the current return.
Touching the down ground is no different than touching the kitchen faucet. :smile: