[sci.electronics] grounding by pipe

dkukral@encad.Wichita.NCR.COM (Dean Kukral) (07/21/89)

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,
you must have a way of disconnecting from the grid feed.  In case a
utility workman were working on the lines (which he thought were safe)
he could get zapped by your generator.

guncer@nunki.usc.edu (Selim Guncer) (07/22/89)

how about using the "ground" as ground (:-)).  back home (in Turkey),
as new ee majors, we were operating our electric heaters by connecting
one end to the live terminal, and the other end buried in the front
garden. since the return path was not provided, we weren't charged for
the electricity! ofcourse, whoever did happen to jump over the fence
and step in the garden may have been electrocuted.

selimg
___________________________________________________________________________
Selim E. Guncer  guncer@girtab.usc.edu

Bir vapur gecer, bogaza dogru... 

john@stiatl.UUCP (John DeArmond) (07/24/89)

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!!! 

michael@xanadu.COM (Michael McClary) (08/12/89)

In article <4474@merlin.usc.edu> guncer@nunki.usc.edu (Selim Guncer) writes:
>how about using the "ground" as ground (:-)).  back home (in Turkey),
>as new ee majors, we were operating our electric heaters by connecting
>one end to the live terminal, and the other end buried in the front
>garden. since the return path was not provided, we weren't charged for
>the electricity! ofcourse, whoever did happen to jump over the fence
>and step in the garden may have been electrocuted.

If they provided service and meters of the same sort as you find in
the U.S., you paid for the energy you used in the heater, plus the
energy lost heating the ground.

The typical watthour meter has two current windings (one for each of
the hot sides of a 220 center-tapped feed), and one voltage winding
(connected between the two hot lines).

When you draw power between the two hot lines, the current is counted
twice (once for each winding).  When you draw power from one side and
return it through neutral, it only gets counted once.  If the neutral's
voltage is exactly halfway between the two hot feeds, you got exactly
half the power, so it comes out right.

If the neutral is a little off, say because of voltage drop from a
crummy connection, you get to pay for the power lost in the voltage
drop as well.  (If it's off to one side because you're placing a
light load on one side and your neighbor is placing a heavy load
on the other, he gets to pay a smidgeon of your bill.)

In a 110 feed (rather than a center-tapped 220 feed), you may find
the meter wired so both the neutral and the hot side go through
current windings.  In this case, you save half your bill by
bypassing the neutral current winding.  (If it's wired with just
one current winding, though, you're back to the same case as the
220 feed.)

-	-	-	-	-	-	-	-	-

msmith@topaz.rutgers.edu (Mark Robert Smith) (08/13/89)

By the Way, can anyone reccommend a good source for a book explaining
the nuts and bolts of power transmission (esp. in the US)?  I'd like
to read up on this stuff, just for curiosity.

I'm looking for info on the whole system, from generation to the wall
outlet.  

Thanks.

Mark
-- 
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