[AT] grounds

[charlie hill]

Charlie,  the house I live in is 50+ years old and has had several owners. 
A few years ago I was in the shower.  Everything was fine until I started to 
turn off the water.  When I touched the knobs I got a heck of a jolt.  I 
managed to get them turned off, got dressed and found my multi-meter.  At 
first I had no current in the shower, then all of a sudden I had 60 Volts 
between the knobs and the cast iron bath tub.  Then the current was gone 
again.  Some thinking and searching lead me to a utility closet that houses 
the oil furnace and the hot water heater.  The furnace was running.  I 
checked and had 120 V between the furnace cabinet and the water heater 
cabinet.

When I finally figured it out here is what was wrong.  First off someone had 
replaced part of the galvanized cold water supply piping to the hot water 
heater with PVC.  Then over time 120 V wiring for the furnace fan had rubbed 
on the housing until it rubbed through the cloth insulation on the 50's 
vintage wiring.  When the furnace fan would come on the fan voltage was 
trying to go to ground on the furnace cabinet but the house ground circuit 
was broken so the stray current was flowing through the hot water heater and 
going to ground through me when I tried to turn the water off.  The furnace 
fan had not been running when I turned the water on.

Luckily I was able to figure it out and get it fixed without anyone getting 
hurt.

Charlie
----- Original Message ----- 
From: "CEE VILL" <cvee60 at hotmail.com>
To: <at at lists.antique-tractor.com>
Sent: Saturday, December 15, 2007 10:44 AM
Subject: [AT] grounds






________________________________
From: cvee60 at hotmail.com
To: at at lists.antique-tractor.com
Subject: RE: [AT] grounds
Date: Sat, 15 Dec 2007 07:56:45 -0500


Mattias, you are right. In addition to the power company ground, the 
National electric code requires not only one ground rod, but two which are 
located a minimum of six or ten feet apart. (can't remember). Additionally, 
any sub service (barn, shop , garage, etc.) must also have a ground 
connection to its own copper rod / rods. Galvanized water pipes from in 
ground service used to be commonly used as a second ground point, but are no 
longer approved. Too much plastic plumbing both for water and natural gas 
and therefore unreliable. We may be getting confused here between common 
ground and equipment ground. Although they may all end up connected to the 
same ground point, common ground purely gives a path to make the electricity 
work, while equipment ground is meant to provide a ready path to stray 
current and prevent electrical shock to the machine user.

To the textbook guys on the list: This is from only my understanding of the 
subject. Please forgive any incorrect terminology.

Charlie




> Date: Sat, 15 Dec 2007 09:04:46 +0100
> From: davidbrown950 at gmail.com
> To: at at lists.antique-tractor.com
> Subject: Re: [AT] : Ice Storm
>
> Henry? Am I right in assuming then that in the USA every house/electrical
> has it's own grounding point opposite to how it works here. Because here
> you got to have a switch that disconnects your own electrical system from
> the net when connecting a generator. Since we have ground in the net I 
> then
> have to have my own groundingpoint (All that copper in the cround).
>
> John If the depth are enough depends on the kind of ground you got. There
> are a lot of complex measuring to decide that.
>
> Though I have a lot knowledge about this but not being an electrician(My 
> dad
> is, I've actually worked as one :-o, and I've got a bunch of education to 
> my
> teflon-brain). I will not try to understand or explain the floating 
> neutral
> potential phenomenon (or something like that) that an electrician friend 
> of
> mine tried to explain to me. Anyway this has made electrical macinery like
> fridges overheat and burning down houses here so be careful.
>
> /Mattias
>
>
>

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