[AT] grounds/shower

[Dave Merchant]

We had it happen a couple years ago.

Standard US feed from the pole, 2 hot legs + neutral, 110 v from either hot 
leg to neutral,
and 220 v across the 2 hots. In this case, the neutral was bare galvanized 
stranded,
and also the mechanical support for the 2 hot wires. Tree fell on the line, 
the 2 hot wires
stretched, and the neutral broke. Not many devices were turned on at the time,
but they saw the 220 v in series due to the floating neutral, they acted as 
a group
of voltage dividers, some saw way over 110 v and burned out (no fire, 
fortunately).

I drove a ground stake quite a few years ago, after I realized that the 
water supply pipes
had been switched from iron to PVC. About time to check it I suspect.
Apparently current NEC wants 2 ground stakes separated by 6+ feet.

Also, regarding something Mattias said, I've been told many parts of the 
world require
switching off neutral at the same time as switching hot. Many US electrical 
people think
it makes no sense, leaves you with the floating neutral issue, but it's 
legislated.

Dave Merchant


At 06:52 PM 12/17/2007, Howard Weeks wrote:
>Any of you ever run into a situation where the neutral lead between
>the transformer and the house was open?
>
>Causes some very interesting problems.
>
>Howard in GA
>
>On 16 Dec 2007 at 21:57, CEE VILL wrote:
>
> >
> > You were pretty lucky to get that jab when you did, Charlie, in order 
> to know about the problem. It is probably lucky you were not sitting in a 
> tub full of water when you touched the faucet. The sequence of events 
> almost sounds like the insurance commercial on TV a few years back with 
> something falling down the stairs, etc.  It sure was thoughtful of you to 
> allow a path for the current trapped in the supply side to the drain 
> side.  (grin). That surely demonstrates where the thinking for that small 
> part of the NEC comes from.
> >
> > Connections to ground rods should be periodically checked as 
> well.  Over time they can loosen and corrode.  I have seen the clamp just 
> sitting on the rod without being fastened at all. The entire system must 
> have been working only from the power company ground, or the fact it was 
> a steel building.
> >
> > We had a situation at work once where not enough supply was available 
> to an entire shop area.  Machine motors were overheating and breakers 
> were tripping.  Maintenance decided the wiring was not heavy enough.  The 
> solution was going to be to transform the current from 220 to 440, then 
> transform it back to 220 at that area.  I suggested someone was not 
> seeing the whole picture, because the wiring was satisfactory for 10 
> years or more with just as many machines.  Another company was brought in 
> to check it out.  Guess what?  Poor connection at the ground 
> stakes.  Hats off to Farmer on this one.  Check the grounds, check the 
> grounds, check the grounds.  That plant area is still up and running now 
> with the same wiring.
> >
> > Thanks for your story.  It makes us stop and think about the situations 
> that can occur.
> >
> > Charlie
> >
> >
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Dave Merchant
kosh at nesys.com
nesys_com at ameritech.net

http://www.nesys.com
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