Hi everyone,
Sorry to keep going on about this same topic, but I just couldn?t let this
one die while I thought so many people have a misunderstanding on the
subject. I?m relatively new to ham radio, and joined this reflector to learn
more about amplifiers, but I do know electrical.
I think that many people don?t know the difference between a ?chassis
ground?, and an ?equipment ground?. The symbol for a chassis ground looks
something like this:
_I_
/ / /
The symbol for an equipment ground looks something like this:
_I_
=
Sorry for the poor representations, it?s the best I could do with a
keyboard, but I think you can figure it out.
A chassis ground is not a ground at all. A chassis ground is a neutral,
or common conductor. The chassis is used as this common conductor for ease
of construction. It allows the manufacturer to do a lot less wiring. The AC
line connection to this chassis ground will carry the imbalance between the
2 hot conductors back to the panel. This conductor is defined by code as a
neutral conductor, and is necessary for proper operation of the amplifier.
An equipment ground is not necessary for the operation of the amplifier,
but does make it safer. The NEC forbids using the equipment ground as a
conductor. The equipment ground should be bonded to the amplifier case,
which should be isolated from the chassis that the components are mounted
to.
A local man knew just enough about electricity to be dangerous. He knew
that the neutral was tied to ground in the panel, and tied the two together
elsewhere when he lost continuity on one. He learned just how little he knew
when it resulted in his daughter?s death. Some of my best customers are
former do-it-yourselfers that learned the hard way to call an expert.
A few of the reasons a ground should not be used as a conductor are:
1. Grounds are often sized smaller than the conductors.
2. A ground may be run by itself, and a conductor may never be.
3. Grounds may take a path not allowed for conductors.
4. Conductors require more protection from physical damage than
grounds.
5. A ground may be something other than wire for part of it?s
length.
I looked in my ARRL Handbook at an amplifier plan. It showed a 4 wire
plug being used, with the chassis ground attached to the neutral, but did
not show what to do with the equipment ground wire. I looked at my recently
acquired Dentron DTR 2000L. It has a 3 wire plug, but no U.L. approval.
Any amplifier, regardless of brand, or performance is poorly designed if
it cannot obtain an U.L. approval due to the fact it forces you to use the
equipment ground as a conductor.
So there?s my 2 cents.
Jim Smith, KQ6UV
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