> So then you are trying to convince us that anyone who has
> a 240V dryer, range, AC, Air Compressor or similar device
> with the neutral tied to the ground at the wall outlet and
> at the device has a safety issue.>
Carl,
That's correct and not just for appliances. Here's one real world potential
problem: If a 120V blower is used in a 240 VAC amp (e.g., older Alpha &
Henry), and one lead of the blower is connected to chassis as the neutral +
ground connection -- and if the neutral opens, current for the blower will
find its way to the load center through your grounded RCA, SO-239, BNC, or
any other chassis-grounded connector.
These amps call for 4-wire service (L1, L2, N, G) and not just 3-wire (L1,
L2, G). The current for the 120VAC portion of the circuit must flow only on
the neutral and not the ground. What is counter-intuitive for most people
is that since ground and neutral are correctly tied together at one place -
the service entrance, that it's tempting to treat one as the other and
ignore the purpose of the neutral and ground and why they must be treated
differently at the equipment end.
Certainly, an amp will work fine when the neutral and ground is tied
together. Want evidence? Thousands of Alpha 70, 77 and 77Dx/Sx amps were
wired this way from the factory and thousands are still being used in away
that violate NEC: What's really scary is the vast majority of ops using
these amps are using only the electrical outlet ground lead and not a
separate neutral. In these cases, all 120 VAC current for the blower is
routed down the ground lead. But as long as that return lead for the
blower is tied to the chassis, current is flowing through all kinds of paths
you may never have dreamed of. The only thing that keeps these amps from
causing harm to the operator is that generally the Z is low enough through
the electrical outlet ground that little return current is flowing though
the panel BNC, RF, and RCA panel connectors.
In all fairness to Alpha's legacy, I suspect these older amps were
manufactured prior to strict integration of NEC and related local codes.
For these amps there are two options: (i) replace the blower with a 240VAC
unit; or (ii) separate ground and neutral. On Alpha amps, option (ii) is
very easy as the disconnect between ground and neutral can be made external
to the amp on the Cinch-Jones power plug. The big headache with this option
is that it requires a 4-wire cable pull into the shack. Both of my Alpha
70-series amps were changed this way without having to touch a single
cabinet screw. For any new shack wiring, I strongly suggest installing
4-wire cabling to cover your bases now, and in the future.
This discussion comes up frequently here on AMPS. A review of the archives
will produce posts that tell the same story.
Paul, W9AC
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