The power company Troubleshooter had come out and turned off the transformers to the electrical service with a special fiberglass rod which opened internal switches in the transformers .We measured with testers and had no voltage . But when we undid the first neutral wire all of a sudden there was a sustainable voltage of 400 volts on the wires which shocked us.
Puzzled we called the power company back up who sent a trouble shooter out and who also measured the voltage and then put a set of grounding jumpers on the transformers to get rid of the stray voltage as he called it from the 28 ,000 volt down to 208 volt transformers which he called Ferrorresonance .
In our case it was determined the jumpers should have been in place before we started the job and the first trouble shooter was written up.
With many new regulations in NEC 70E Electrical safety practices for workers which came on line a few years back it is mandatory to now use them on many jobs.
to prevent exactly what happened to me and electricians I was working with.
While the use of jumpers has always been taught as a practice to prevent an accidental electrocution should a service line be turned on by mistake while it is being worked on and the jumpers will cause the over-current protection to trip out .As more and more complex power systems come on line jumpers there ability to eliminate stray and transformed voltages has become much more recognized. But as with any safety equipment jumpers must be properly and carefully placed to operate properly or you can cause serious injury's or death.
|Example of jumpers set being installed on overhead lines to protect workers down stream in case the overhead lines would become energized|