I'm not an electrician, but I think there's some bad poop happening on this
topic. The latest comment from Rich Measures, "Neutral is grounded at the
breaker box.", could lead someone to believe it's OK to use neutral as
chassis ground.
While Rich is 100% right in terms of how things should be connected at the
breaker box, you should not use the neutral as chassis ground.
I was taught that neutral is NOT ground - in that the circuit should never
be connected such that the ground will carry current. This is especially
important in Ground Fault systems.
In a device that requires both 240V and 120V, it will require the neutral as
the current return for the 120V and a ground. Therefore will require 4
wires: "A" phase, "B" phase, Neutral and Ground.
Example: I have a KWS-1, it needs 240V for the HV xfmr and 120V for
everything else. Inside the box, the "cold" side of the 120V devices
(neutral) is not connected to chassis ground. To properly connect it to the
mains requires 4 wires. ("A" phase, "B" phase, neutral, ground) I believe
that back in 1957 KWS-1's were built with 3-wire cords - no chassis ground -
that doesn't make 'em right.
There are other amps which use primary taps, dropping resistors, etc. to
'generate' 120V internally (TenTec Titan comes to mind for it's blower and
AC control) - these only need 3 wires ("A" phase, "B" phase, ground).
There are a bunch of different 4-wire plugs available. Some are marked
3-phase ("A" phase, "B" phase, "C" phase, ground), some are marked 2-phase
("A" phase, "B" phase, neutral, ground). The pin structures are different.
I suspect very few of us have 3-phase in our homes so using the 'wrong' plug
and socket are not problematic (as in plugging a 3-phase device into a
2-phase circuit) - just wrong.
Punch line: use 4 wire if you need 240V and 120V, no current flow on the
ground, use the right plug & socket.
All this said.... I certainly get a kick out of the typical back-and-forth
that happens here. Plus I think I learn a lot too. Happy Holidays to all.
Best 73, Bill N2BC
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