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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: electrical deaths
Date: Mon, 2 Dec 2024 19:36:33 -0700
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On 12/2/2024 2:17 PM, Joe Gwinn wrote:
>> Polarization can save the day with toasters and similar appliances. Then
>> you can make sure that neutral comes in at the top end of the meanders.
>> In the US, 99+ percent of cases will not have line and neutral reversed.
> 
> I think that the 99+ percent is quite optimistic, especially on older

And on buidings where one (or more) homeowners THOUGHT they knew
enough about "electricity" to be able to make their own repairs.

We had a light switch in the garage that "went nowhere".  Another
light switch that would SOMETIMES result in a shock -- if you touched
the metallic portion of the switch assembly!

Apparently, the "nowhere" switch was originally a "three way" (SPDT)
switch, but some previous owner had replaced it with a regular (SPST)
switch.  When faced with the third conductor (one of the two travelers)
he opted to connect it to the third screw on the switch -- the "earth".

So, depending on which position the switch was in, the "earth" of the
other would be directly connected to the line.  Because all the Jboxes
were plastic, nothing ever went "pop".

> buildings.  Back when I was an apartment-dweller, ran into all manner
> of trouble, to the point that one of the first things I did in a new
> apartment, was to turn the power off and opened all electric boxes,
> and straighten out the "carpenter wiring", much of this being
> dangerous.

When I wired this place with network cable (5000 ft!), I found a
#12 length of ROMEX heading down into the wall cavity.  On one side,
was a floor to ceiling window.  On the other, cabinets.  I.e., there's
no place this could be going!

And, there wasn't!  When they built the house, there was supposed to
be an outlet along the side of the window.  Wire was there.  Electrons
flowing through it.  Just no "fixture" attached to the end!

<frown>

SWMBO's home had an outlet that she claimed "blew up Tracy's microwave
oven".  "Not possible", I replied.

Turned out that the guy who had wired her kitchen during the remodel
had run a single 12/3 w/GND around the counter area.  He would pick
up one leg and neutral (plus earth) for THIS outlet, then the other
leg and neutral (plus earth) for the next outlet, etc.

For the outlet in question, he picked up both legs (plus earth), but
NO neutral.   Oooops!

So, whether its the "professional" or the "amateur", one should be
wary of actual conditions and not expect them to be "as prescribed".

> War Story One:  In the 1970s in Washington, DC, my boss was having
> considerable problems with the lights in his newish house in the
> suburbs.  For instance, when he turned one light on, an unrelated
> light would go off.  I said it sounded like some kind of grounding
> problem.  Eventually he invited me to dinner in his house, and bring
> your voltmeter.  Which I did.  It turned out that the solid copper
> wires at every electrical device (wall switch, outlet, light, et al)
> were loose - the electrician (or his assistant had forgotten to
> tighten all the terminal screws down.  (Stranded wire was not used
> then.)  So boss called the builder to have all those neglected
> terminal screws tightened properly.  He was lucky that there wasn't a
> fire.

A neighbor had exactly that problem -- and exactly that unwanted outcome.
It was an interesting situation to analyze:  what should he do before the
fire department got there?  Try to kill the power with the main breaker?

Ans:  absolutely nothing; you have no idea what might be hot, now, given
that earth has failed!