[TenTec] [Amps] what is a 4 wire 240VAC service?

[Ken Brown]

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