I am currently working on a project in Flagstaff, Arizona that involves
the installation of a standby generator with a remote control panel. During the startup phase of the
installation the manufacturer's representative disconnected the battery negative ground jumper. He
said that since he would have to disconnect the batteries several times during the startup and tests
that it would eliminate the possibility of a battery short. The batteries are two parallel sets of
two batteries in series with a potential of over 13,000 amps at 24 volts. The first time he disconnected
the batteries he pulled off one of the positive cables first, and dropped it behind the batteries.
The cable met a conduit from the control panel, with the second cable still attached to the batteries.
The fault current back fed the microprocessor through the ground and found a #14 control wire tied
to the battery negative. The result was a fire in the control panel that burned a bundle of approximately
ninety #14 wires. It took half of the day to replace the wires; fortunately, there was no damage to
the microprocessor. The representative said that removing the negative ground jumper was standard
procedure, and that he had never had a problem before. All I can say is that it does not seem like
a very good practice. It would be better to follow the practice of removing the negative cables first,
as you were taught in auto shop.
Corbins Service Electric