Jim Brown wrote:
> That violates all the building codes I know about. A mains power circuit
> must have a phase, a neutral, and an equipment ground (green wire), and
> they must follow the same path.
I don't think you need a neutral (ground*ed* conductor).. two hots and
ground will do. (three phase motors have three hots and a ground, for
instance)
And then, is a grounding conductor needed even for an isolated circuit?
There's all sorts of weird rules for isolated circuits, and in this
case, the green wire ground is created brand new at the utilization
equipment, so the safety issue is addressed (i.e. the case of the
equipment is at "bare feet on floor" potential).
here's some likely references..
Art 250.21 Alternating-Current Systems of 50 Volts to 1000 Volts Not
Required to Be Grounded
Art 250.22 Circuits Not to Be Grounded
Art 250.30 Grounding Separately Derived Alternating-Current Systems
I wouldn't recommend it, but there are some unusual situations
contemplated in the code. e.g. street lighting with constant current
sources and the lamps all in series.. Another example is neon signs,
which have just the two HV wires and no ground. The transformer has a
grounded centertap on the secondary. Of course, the wire is rated for
15kV (twice the actual voltage to ground) AND the new codes require
GFCIs as well. Some health care systems also aren't grounded (to
prevent the possibility of leakage current through an electrode
connected to test equipment killing someone)
>
> Again, this is above and beyond the issues of the rating of that cable for
> use in power systems (VERY unlikely) and the STUPID factor that the ex-
> broadcast engineer pointed out, and the liability issue.
You betcha...
I'd never do it, and if someone wants to do it, I'd suggest they
carefully read the code (and the rationales and explanations), and then
think long and hard, and *then* not do it.
Jim, W6RMK
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