Why the requirement for separate ground and neutral wires is reasonable
and not just the "result of nanny state busybodies."
In a device that runs on 240 VAC the currents in the two hot wires are
equal magnitude and opposite phase. No current flows in the ground wire,
except in the case of a fault. The I * R voltage drop in the ground wire
is zero, since I = 0. This keeps the chassis of the device at ground
potential, zero volts relative to ground. This is a three wire system,
which is safe and conforms to present day codes.
If there is a portion of the equipment (such as a motor, clock or
control circuitry) which is run on 120 VAC, not using a 240 / 120 step
down transformer inside the device, powered by one hot lead and using
the ground wire as the return, the current in the ground wire is not
zero. The I * R voltage drop in the ground wire is some finite value
greater than zero, and the chassis of the device is at some potential
greater than zero volts relative to ground. This is an unsafe system
which does not conform to present day codes.
If there is a separate neutral wire for the 120 VAC load(s) in the
device AND a ground wire, the ground wire carries no current, except in
the case of a fault. The I * R voltage drop in the ground wire is zero,
since I = 0. This keeps the chassis of the device at ground potential,
zero volts relative to ground. This is a four wire system which conforms
to present day codes.
DE N6KB
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