The thing here is that the low side of the power is supposed to be ground
but doesn't have to be at any point that you can see.
There is a seperate safety ground which does get connected to ground at
several points and eventually gets connected to earth ground. This line is
for the safety of the operator of the equipment and isn't designed to carry
any of the power used by the equipment. It's purpose is to make the
equipment chassis at the ground potential so that you don't get shocked by
operatiing the equipment.

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Why isn't there an Ozone Hole at the NORTH Pole?