[AMRadio] AMRadio Digest, Vol 90, Issue 22

[D. Chester]

>> Electric kitchen ranges with 3-wire plug run on 240V, with the neutral 
>> and
>> ground bonded together.  So does the BC1-T broadcast transmitter in 
>> original configuration.

> And, so does the Alpha 70 and 77 series of HF amps -- along with some of 
> the
> big Henry models.  In the case of each amp, neutral is used to run a 
> 120VAC
> blower.  In the Alpha 70/77 they made it easy to separate neutral from
> chassis ground by cutting a jumper on the Cinch-Jones power plug.  The
> change doesn't even occur inside the amp.  I ran 4-wire, #8 AWG between 
> the
> panel and the shack, terminating into a 30-amp twist-lock receptacle.  My
> only dilemma is that I have one receptacle and four amps, requiring a
> physical change of the power plug when changing between amps.  No really
> good solution comes to mind, mostly for convenience reasons.
>
> At the time these devices were manufactured, it was acceptable to join the
> chassis to the neutral connection.  40+ years ago, the NEC may have 
> strictly
> forbidden this practice, but the NEC is a premise wiring standard -- not a
> products wiring standard.  So, perhaps the root of this really goes back 
> to
> what was allowed  under UL guidelines at the time.  Well after 1970, the
> manufacturers seem to have gotten the idea and had found a means to better
> utilize the blower between 120VAC and 240VAC service.
>
> Paul, W9AC

Strapping neutral to ground at any point beyond the entrance panel is not 
only a safety hazard; it can wreak havoc with certain equipment by causing 
ground loops. Ideally, if I could find them, I would use heavy duty 240 
to120v isolation transformers, each with a mid-tapped 120v secondary, to run 
all the 120v stuff in the house. Of course, that would run up the power bill 
slightly because transformers are not 100% efficient and each one would have 
a little power  loss. With balanced 120v lines, the biggest jolt you could 
get from hot to ground would be 60 volts, and the balanced line would take 
care of  most of the ground loop problems. I understand the navy uses 
balanced 120 volts on shipboard just for that - safety reasons.

A lot of our ground loop and ground fault problems would not exist if the 
mains voltage were universally 240v to run everything, and the mid-tap on 
the pole pig secondary were strictly a safety ground and we never tried to 
pull any current through it. Every appliance would have a 3-prong plug: two 
hots and a ground. That's the way they do it in many countries round the 
world with no problem. It would also save energy by reducing the voltage sag 
in wiring. I suspect our 120/240 system was already too well established to 
change before all the problems became apparent, so the best we could do was 
to add the requirement for separate ground and neutral.  Old 220v 
receptacles had nothing but two "hot" prongs,  but they lined up differently 
from the ones on110v plugs so the wrong appliance couldn't be plugged in to 
the wrong voltage.

This house was first wired in the 1930s, and none of the original wiring 
even has a ground conductor. All the original outlets are two-prong only. 
Unfortunately, they didn't use knob-and-tube wiring, but what was at that 
time supposed to be the latest and greatest: that old style romex-like stuff 
with rubber insulation covered with tar-impregnated cloth. The dried-out 
insulation on the old wiring is very fragile and brittle, but it would 
require ripping through walls and ripping up floor boards to replace it, so 
I have always been content to just be careful with it. Every connection was 
soldered, which I think is better than those flaky wire nuts that can cause 
a fire if they are not assembled and tightened properly, and leave a loose 
connection that eventually begins to arc. Knob-and-tube, if installed 
properly and not tampered with, should never fail even if the insulation 
dries up and falls completely off the wire.

Paul, why couldn't you just wire in three more  receptacles so you would 
have a separate one to accommodate each of your amps, and not have to do all 
that plugging and unplugging  nonsense? You could even make it work like a 
power strip, with one heavy duty plug connected to the main receptacle, and 
a cable feeding four additional surface-mount receptacles mounted side by 
side on a board or metal panel.

Don k4kyv


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