ground rod question [RE-wrenches]

[Ray Walters]

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Phil Undercuffler wrote:

>Darryl Thayer said <snip> 
>As I see it the ground rod on a PV array is for two purposes, .... Two to
>protect grounded people from any errant voltages/currents that they might
>contact during fault conditons.  (part two is what the electrical inspector
>is looking for).....
>
>Actually, this is one function the ground rod does NOT perform.  The bonded
>conductor (neutral or negative, generally) provides the return current path
>for any fault current, which trips the fuse or breaker thereby clearing the
>fault.  
>
>  
>
No offense,  Phil , but Daryl was right too. The frame grounding is also to direct stray current to ground.
Many shorts to framing will NOT be enough amperage to trip the breaker. A mere 100mA can cause death. I have measured such stray
currents on ungrounded framing in the under 1 amp range. The solution is to ground all exposed metal.  If a dead short (fault connection capable of carrying full current) has occured then yes, the breaker will trip as Phil stated, because neutral is bonded to ground. 

>If you make a short between hot to ground (Please don't attempt this at
>home), the breaker will trip no matter whether the ground rod is connected
>or not. 
>
Sorry that's not quite right. If its not grounded, then that bare copper 
wire is just bare copper wire, its not at ground potential. If the 
grounding system is not tied to a ground rod, the breaker might trip on 
hot to the bare copper wire, but it will not trip if there is a short to 
other grounded metal. I had first hand experience with this. A nail was 
shorting hot to the lathe in the wall. The ground wire was not attached 
to the rod. As soon as I  connected to ground, and reconnected power, 
the breaker tripped. (dead short) This system had been quietly 
energizing the lathe (at ground or earth potential) for 5 years without 
tripping the breaker.

> However, if you remove the bond between the grounded conductor and
>the equipment ground, the breaker won't trip no matter how many ground rods
>you drive, thereby presenting potential voltage hazards to your grounded
>people--and we all know how hard it is to find well grounded people
>sometimes, so you don't want to waste them ;-)
>  
>
All Very True.

More on running Array grounds outside the conduit:

I too, have run the ground ( bare #6) outside the conduit to increase 
earth contact. The problem is, I've heard inspectors want to see the
equipment grounding conductor run with the other conductors. That means 
that it should be IN the conduit. Maybe we would keep the 6 out in the
ditch and run a green 10 in the conduit to satisfy a picky inspector?
(the 10 would be the equipment grounding conductor, and the 6 would be a 
ground rod to rod bonding jumper?)
And don't get your hopes up, I had a system with hundreds of feet of 
bare 6 in the ditch, several rods tied together, etc. but the soil
was rocky and dry. Lightning came in on the wind generator, ran (IMHO) 
through all that bare ground wire and took out everything that was
grounded to it: generator controls, charge controller, SW inverters,etc. 
After that, we tied that mess of copper to a steel cased well a
1/2 mile away (you read right) and we haven't had any more problems in 6 
years.
Get a ground impedance tester, if you want to be serious. Everything 
else (besides a steel well casing) is guess work.

Also, Dan, while a pole mounted array could qualify as a separate 
structure with its own grounding electrode,  I think it could also 
qualify as
part of the integrated system, and not be required to have its own 
ground rod. Read the definition of Premises Wiring (System) article 100. 
It reads:
That interior and exterior wiring, including power, lighting, control, 
and signal circuit wiring together with all their associated hardware, 
fittings......that extends from the service point or source of power, 
such as a battery, *_a solar photovoltaic system_*, ...... to the 
outlets. ........

I believe that means it is all one system with one integrated grounding 
system. I usually sink a rod by the array anyway, but our inspector at 
least has never required it.

Just muddying the already turbid waters of grounding theory,

Ray Walters


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