Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Polarized Plugs for 120 VAC
Message-ID: <1988Nov13.000833.21883@utzoo.uucp>
Organization: U of Toronto Zoology
References: <686@bnlux0.bnl.gov>
Date: Sun, 13 Nov 88 00:08:33 GMT

In article <686@bnlux0.bnl.gov> nagy@bnlux0.bnl.gov (John Nagy) writes:
>Relative to a cold water pipe or a puddle of water on the floor
>there is a big difference.  A human simultaneously touching
>a pipe and a white (neutral) wire should experience no shock.

Urk!  No!  Don't make this mistake!  Why do you think there are separate
ground and neutral wires anyway?!?  The neutral wire should indeed be
grounded at building entry, *but* remember Ohm's Law:  that wire may
be carrying substantial return current from running devices, and its
resistance is not zero!  At a point remote from the building entry, the
neutral wire may have a substantial voltage with respect to ground.
That is, if you touch pipe and neutral wire, some of that return current
may try to flow through you rather than through the wire, because you
are providing a shorter path to ground.

This is particularly true in a large building.  Last time I checked, I
measured something like 10 volts between neutral and ground in my
apartment building.

Connecting (say) the chassis of a TV set to neutral is a whole lot safer
than connecting it to the hot wire.  However, it is **NOT** the same as
connecting it to ground.  NEUTRAL IS NOT GROUND!
-- 
Sendmail is a bug,             |     Henry Spencer at U of Toronto Zoology
not a feature.                 | uunet!attcan!utzoo!henry henry@zoo.toronto.edu