[Hallicrafters] AC/DC Halli's, Grounds and HUM

[Barry Hauser]

On Wed, 13 Feb 2002 13:06:18 -0800 k6uuz at juno.com (Ed Richards) writes:
> Another safety precaution is to use a 3-wire cord and plug. Connect 
> the safety ground (green) wire to the outside case and the neutral 
> (white) wire to the chassis. (double protection) and the hot (black)
wire to 
> the switch. Sometimes this requires a small change to the wiring of the
> switch. This keeps the cabinet and the chassis grounded all the time 
> and when turned "off" the entire radio is grounded except for one 
> terminal on the switch.

Hi Ed & list:

Gee -- I didn't think tying the neutral and ground together (potentially)
was OK.  Any other opinions on this?

As for Ray's query (Hi Ray), I suspect meaningful stats on AC/DC radio
fatalities may be hard to find.  Then there's the key marketing question
of how low a body count is acceptable per 100,000 units sold -- y'know,
"collateral damage".

Aside from outright burns and fatal electrocution, the other problem is
what else happens when you get a shock.  You learn just how high or far
you can jump.  Sometimes it's the physical injury that results from
explosive reflex action that manifests the damage.  On top of all that,
if you were holding the radio or had your hand on it, it could get
damaged.

Many radios and both old and new appliances can present such a risk.  For
example, the old Echophones have hot chassis attached to the cabinets
with insulated washers -- which could have been left out duriing
reassembly, or deteriorated and crushed, etc.  Many old plastic/bakelite
table radios depend on plastic all around, including the knobs for
protection.  However, the chassis mounting screws that are exposed at the
bottom are potentially live.  Many are pretty safe closed up with cabinet
intact, but battery radios have pop open hatches -- like the
Transoceanics -- which expose the live chassis.  There's no interlock as
with TV sets..

Another (though somewhat less safe) approach is to replace the line cord
with at least a polarized two-prong version.  The hot side should be the
switched side, not the chassis side, and that may call for some minor
rewiring.  Of course, this relies totally on correct outlet polarity. 
Lately though, nearly every appliance comes with a polarized two prong
plug -- even table lamps.  And, they have a warning label on the line
cord about not defeating the polarized plug and making sure outlets are
correctly wired.  Other appliances warn about replacing knobs, loose or
missing parts, etc.  So it would seem, the "issue" is not limited to 50
year old AC/DC radios.

I don't know that it's realistic to hope that all hot chassis (and hot
cabinet) radios will be retrofitted with isolation transformers, but
maybe a practice should be started of attaching a label to the line cord
with a standard warning -- admittedly lame by comparison, but better than
nothing.  If the unit has not yet been fitted with a polarized or
grounded plug, the old plug can be marked as to which side goes to the
hot, or small slot. Of course, the warnings on the new appliances are
intended more for liability control than actual accident prevention. 
Again, it has to do with acceptable levels of collateral damage.

If you don't want to put isolation transformers in all your hot chassis
radios, you can get a high current isolation transformer -- e.g 10 amps,
and use an outlet strip for several of the units at once.  Of course,
that doesn't protect some future owner.

Sorry for the lack of brevity, but one more curious thing.  One modern
day equivalent of the hot chassis "solution" is the wall wart.  Notice
how many things have them, in addition to portable, and not so portable
radios?  This takes the AC out of the chassis and cabinet altogether --
so, among other things the appliance itself doesn't have to be hi-pot
tested and UL or CSA listed.  Of course, the vast majority of wall warts
never power off (primaries connected 24/7) and were sited by our
President as being "power vampires" slowly sucking out megawatt-hours by
the milliwatt.  Not to mention -- did you ever see one with a fuse?  I
wonder what the stats are on those -- where they burn before tripping a
breaker?

Barry
Always with one hand in a pocket, and, uh, the other hand in the other
pocket.