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Re: Lightning and neutral grounding



Theoretical perspective:

There are definitely circumstances where the neutral wire is carrying 
current and may have some AC voltage on it.  The neutral wiring is also 
intended to be the *normal* return path for current going to appliances 
on the hot wiring, whichever phase it's on.  Depending on where you tap 
into a neutral, you may see all sorts of trash on it from higher-demand 
appliances closer to the panel on your circuit.

You also create ground loops and possibly apply voltage to the safety 
ground if you tie it to the neutral anywhere but at the main service 
entrance.  The principal function of the safety ground in a residential 
electrical system is to force a breaker to trip if a hot wire comes 
loose and comes in contact with an outlet box or the outside metal 
housing of an appliance.  There's a small but nonetheless real risk 
that it may not do that if the safety ground is tied to anything 
elsewhere in the system.

Needless to say GFCI outlets and breakers are another compelling reason 
to keep the safety ground separate -- they work by comparing hot 
current to neutral current and if you upset that balance you may see 
very frequent nuisance trips of a GFCI breaker.

That being said .. practical perspective:

The NEC is almost universally recognized by most insurance carriers, 
fire departments, and other entities not specifically interested in the 
details of electrical engineering but responsible for safety, as a 
standard of good design practice.  It may not be a perfect standard, 
and there may be unusual circumstances where there might be a better 
and safer way of doing things that happens to go against it, but for 
the sake of compatibility with other people's practices and pure CYA, 
it's better to follow it.  I could tell the story of the work crew 
drilling a well that had to stop, drive a ground rod, and ground the 
drill motor that already had the best ground return in the entire 
county through its 30-40 foot string of drill pipe, but aside from 
being good for a laugh, it just illustrates the point ..

On Tuesday, Mar 11, 2003, at 15:11 US/Central, kb9cry@attbi.com wrote:

>
>
> If the neutral in AC wiring is eventually connected to ground at the 
> service
> entrance, why have a third line that is grounded anyhow.  Why not just
> ground through neutral?
>
> Theoretically this it true but I've asked every electrician I've ever 
> known and
> they all are brain-washed into saying, "But that's not in accordance 
> with
> NEC."  And I now believe it too.  Because the code says so.  Period. 
> And, once
> again, in three phase power applications, you can come up with many 
> examples
> where a load will become inbalanced  or a back feeding situation 
> develops and
> the neutral will end up carrying some current.  So the fourth ground 
> wire is
> required to protect the operator from electrical shock and/or to 
> provide a
> ground path back to the breaker so it can operate correctly.  In a nut 
> shell,
> no, don't do it.
> ----
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>
"Many that live deserve death. And some that die deserve
life. Can you give it to them? Then do not be too eager to deal out
death in judgement. Even the very wise cannot see all ends." -- Gandalf

----
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