🚀 go-pugleaf

In article <178@zip.eecs.umich.edu> don@zip.eecs.umich.edu.UUCP (Don Winsor) writes:
>
>I've run into a poor wiring job in an older house belonging to
>friends where I found a multitude of sins.  One of them was that
>some grounded receptacles were wired with old two conductor cable
>and they just had the neutral and ground pins tied together at
>the receptacles.  In the interests of safety I suggested they
>pull modern NM cable to these receptacles, which didn't seem too
>hard to do, since there was easy access down through the wall and
>into the (unfinished) basement.  My friend didn't think this was
>necessary, and I couldn't come up with a good, convincing argument
>that this was a bad idea.  His line of reasoning was that the
>ground and neutral wires all went to the same bus bar on the
>main breaker panel, so running another conductor offered no
>advantage.  Can anyone offer a good, clear, convincing argument
>to refute this?  About the best I could think of was if the neutral
>wire got broken somewhere between the breaker panel and the
>receptacle, and you then plugged a low resistance device with a
>grounded case into the outlet (say an electric drill with a three
>prong cord in a metal case), there could be a significant leakage
>path from hot, through the motor windings, out the drill's neutral
>wire, across the neutral-ground tie in the receptacle, and back up
>the drill's ground wire to the drill case.  Thus, we now have a
>hot drill.  Is this the reasoning?  If not, can someone give a
>better explanation as to why "this is worse than nothing at all"?

If you tie the protective ground pin to the neutral, the voltage drop
in the neutral wire (perhaps several volts, even if everything is
within spec) appears on the case of everything connected to the circuit.
If one of the things is a motor, you could find forty volts for a moment
when it starts.  You'll also be looking at fifty volts for a moment when
the circuit is shorted, assuming both neutral and hot have the same
size wire and identical connections.  (But if it's miswired, it's a
good sign there are other problems as well.  And if a neutral wire
connection vaporizes before the breaker goes, the breaker won't go,
and the drill stays at 110 indefinitely.)

It's current that kills, and you CAN do somebody in with 1 1/2 volts
if the connection is good enough.  (Like salty-sweat on your hands,
as you hold the drill and steady yourself against a really-grounded
piece of metal.)  20 amps when the case of your equipment contacts
a real ground might not be good for the finish, either.

(Story circulated when I was at UofMich EE school:  Bunch of freshman
EEs at another school had bet going on whether you could kill
somebody with a single dry cell.  Guy betting "no" put hands into
two buckets of salt water, guy betting "yes" applied 1 1/2 between
buckets.  They couldn't get "no" defibrilated.  R.I.P.)

Ask an EKG operator at your local hospital about "microelectricution"
some time.  Or ask the hospital electrician about the lengths they
go to on the grounding.  (Periodic inspections, transparent plugs
so you can see if the wire comes loose...)  The main thing that
enables you to handle a hundred volts is your skin resistance.
A cut, electrode paste, or a needle through the skin, and you've
gone from several megohms to nearly zero.  Sweat is enough when
you're dealing with house wiring.  20 ma up your left arm and
you'd better have the paramedics onsite, because you won't have
time to call them.