Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!gatech!emory!stiatl!john
From: john@stiatl.UUCP (John DeArmond)
Newsgroups: sci.electronics
Subject: Re: grounding by pipe (was ... true ground?)
Keywords: ground, pipe, electrocution
Message-ID: <6008@stiatl.UUCP>
Date: 23 Jul 89 22:21:47 GMT
References: <741@encad.Wichita.NCR.COM>
Reply-To: john@stiatl.UUCP (John DeArmond)
Distribution: usa
Organization: Sales Technologies Inc., "The Procedure IS the product"
Lines: 42

In article <741@encad.Wichita.NCR.COM> dkukral@encad.Wichita.NCR.COM (Dean Kukral) writes:
>It seems that using pipes as grounding vehicles is fairly common.  Is
>this dangerous to plumbers?  I mean, if there is a short to ground while
>a plumber is working on pipes, couldn't he/she get zapped pretty badly?
>Is this an unlikely event?  Does anyone know of it ever happening?
>
>Related: if you generate electricity via a windmill or other generator,

YES.. This is a serious hazard and yet another reason to avoid water pipes.
One does not have to have a fault to see ground current - there only
has to exist a lower resistance path back to the transformer neutral via
ground than via the neutral leg.  Read on...

I was working on the wiring one day in the old appartment building I 
spoke of earlier.  The breaker box for the unit I lived in was located where
all the utility feeds come in.  The 2nd story of the place had only one 
breaker for the floor which got tripped all the time from window ACs and
hair dryers.  I was in the box measuring loads with a clamp-on ammeter.
I had measured a line and had clamped the unit on an overhead pipe while
I found another wire.  I happened to look up and notice that the amp-clamp
was indicating almost 50 amps!!!!  I initially discounted the reading 
as intereference from all the wiring around.  Then I moved the clamp around
and the reading did not change.  I moved it to the big ground wire comming
from the breaker panel to the "ground" provided by the pipe.  50 amps!!!

To make a long story short, I found that the neutral grounding lead on the
power pole outside had been cut when a car hit it.  The broken line meant 
that neutral current from the whole block was flowing through my neutral
lead, down the ground wire and back to earth via my cold water pipe!!!
Imagine what a shock (pun intended) I'd have gotten had I broken that pipe
for maintenance.  Or consider what would have happened if the ground had dried
out real good and the ground gone high resistance.

Moral:  Let water pipes do what they do best - carry water.  Put a real
ground in separate from the pipes.

john

-- 
John De Armond, WD4OQC                     | Manual? ... What manual ?!? 
Sales Technologies, Inc.    Atlanta, GA    | This is Unix, My son, You 
...!gatech!stiatl!john    **I am the NRA** | just GOTTA Know!!!