I've seen many old installations where the neutral was fused with a discrete
fuse (not a ganged circuit breaker) . It's really easy to open the neutral
in this case. These installations were in residential, institutional, and
industrial settings, and were installed by major electrical engineering
firms of yesteryear. They were all properly grounded. But when the
neutral opened, the results were often spectacular. In these situations,
the neutral sometimes floated to 240v or 208v, but more often, a path to
ground was established through an appliance. A weird "back feed" situation
then occurred because if you turned on an appliance whose resistance was
less than that of the appliance supplying the path to ground, it would work.
If the turned on two appliances, both would go out. A simple voltage
divider but bewildering the first time you see it.
As a young engineer on an industrial site, I remember getting a panic phone
call from some of the operations staff. When they turned on the light it
worked. When they turned on a second (smaller) light, it came on and the
other one went off. Various weird combinations of appliances would work
(the TV and the toaster, but not the airconditioner). Sometimes the order of
turning things on determined what would work. And some of the devices were
on 'different circuits'.
Some of the workers concluded that something evil or supernatural was going
on and left. Of course, I knew immediately what was going on and offered the
following explanation, "What the hell is going on here? What did you do?".
It was an open neutral fuse.
Another incidence, (residential, large apartment building). Occupants were
listening to a phonograph when someone plugged in the toaster. Suddenly the
phonograph sped up to 78 rpm and the incandescent lights got very bright
which was very amusing until the phono let out a puff of smoke and died.
They later noticed that all the other appliances (TV. clocks, radio) were
cooked. Open neutral fuse.
Yes, I had all these immediately rewired, which earned me the enduring
admiration of the occupants (First you burn out all my stuff, now you have
two guys breaking down my walls and I'm in the dark. They weren't impressed
by the elegance of first semester electrical circuit analysis.)
(in New York city, quite a few places still have DC service, a hold over
from the old Edison Electric. You'd be surprised where it turns up, and it
is still in use. ) I've seen people 'just tap of a line for my new
fluorescent light, airconditioner, etc. thinking it was AC. Very interesting
results.
I've also seen many installations where the connections at the panel were
loose (including the neutral).
So, chewing through a #6 or 750 MCM cable is tough, but easier than
swallowing some of my 'war stories'.
----- Original Message -----
From: "R.Measures" <r@somis.org>
To: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>; "AMPS" <amps@contesting.com>
Sent: Friday, December 05, 2003 4:43 AM
Subject: Re: [Amps] 220V service for amplifier
>
>
> >R. Measures wrote:
> >>>If you tie it to the neutral, there is a possibility of a voltage
> >>>differentail between the amp chassis and the earth ground which can
create a
> >>>dangerous situation.
> >>>
> >>** But only if the neutral wire is severed while the radio operator is
> >>standing in water without wearing his fishin' boots.
> >>
> >
> >Getting a shock is much easier than that.
> > ...
> ** Ian -- The neutral wire between the electric-mains' box and my radio
> room is #6 gauge. At least in my experiences, severing #6 isn't even
> close to being easy - - and besides that, the drainage is pretty good.
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