What Jim says here is correct.
The old exception that allowed returning 120V loads to the bare or green
grounding wire of a 240V circuit was very limited, allowed only for a
few large appliances (dryers, stoves/ovens, and water heaters IIRC)
which would be disconnected only for maintenance or replacement. The
exception never applied to ham equipment.
There are at least three possible Bad Things that can happen when you
use a ground to carry operating current:
(1) Some of the 120V load current returns by way of the coax, keying
line, ALC line, the rig and its power supply, the antenna grounding
system, etc.--anything connected to the amplifier chassis. This current
often causes a stubborn hum in your transmitted signal (and other ill
effects).
(2) If the circuit has GFCI protection, the 120V load current is likely
to trip the GFCI.
(3) If the ground wire opens for any reason, the 120V load current has
nowhere to go except the unintended paths, in particular through you if
you are touching anything connected to the amplifier. This danger is the
primary reason the NEC no longer allows combining neutral and ground
conductors anywhere beyond the power service equipment (master
disconnect enclosure).
So if you have an older amplifier wired with 120V loads to chassis, it's
wise to spend the time and money to make it safer and better by keeping
the 120V load currents out of the chassis ground connections.
--Tim (KR0u)
On 12/24/2014 2:50 PM, Jim Brown wrote:
You may be confusing a 120/240 outlet that has a four circuit plug
(phase, phase, neutral, and Green) and can serve both 120V and 240V
loads, with a 240V outlet that has a three circuit plug and serves only
240V loads. There is no neutral in a 240V outlet, and as noted above, it
is illegal to connect a 120V load between one phase and the Green wire
(Equipment Ground). That 120/240 circuit can feed both 120V and 240V
outlets. A neutral IS required to feed those 120V outlets.
---
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