ground rod question [RE-wrenches]

[David Palumbo, Independent Power & Light]

Darryl,

Here's a hypothetical for you.

Off grid system with ground mounted top of pole array located 150'(or more)
from the house.
Do you still run a ground wire back to tie in with the other ground rods?

I have always done it like you state, with two ground rods connected to a #6
bare ground wire (in the trench with the conduit for the transmission wires
(high voltage to MX60)) which is connected to the system ground rods.

Now with copper becoming so dear I certainly do not want to waste it is not
necessary. What say you wrenchers?

David


Hello Peter
Below is my understanding of the codes regrading
grounding.  I have certainly been wrong in the past
and have had many discussions with inspectors on
grounding.
As I see it the ground rod on a PV array is for two
purposes, One to divert any lightening induced surges
to earth protecting your equipment and 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)

For part one The shorter the ground lead the better.
and this is not NEC but NFPA 780  78? the lightening
protection code.  The connection should have only
radius  bends, and a larger outside diameter and of
course a good ground connection.  Y0our array will act
as a capacitor with the sky and as lightening
discharges occur within the county the sky earth
changes potential and your array will have differing
amounts of energy to dissipate.  I always drive two
ground rods and separate them by there sphere of
influence 8 to 10 feet.

In case two the grounding is to protect against any
"generated fault currents" currents from the PV system
or back feed through the system from the Utility or
other source that should happen to get on the frame.
This is the one that the inspector is concerned with.
You have a separately derived system and it needs a
grounding electrode system.  You can either bring the
ground wire back to the service location and ground
the array with one rod or ground with two rods at the
array.  I ALWAYS GROUND AT THE ARRAY AND BERING BACK A
GROUNDING WIRE.  When wiring a garage for example the
ground rod is always placed

Hope this helps and is correct.
Darryl

--- Peter Duchon <info at asappower.com> wrote:

>
> What is the max. distance an 8' ground rod can be
> from a ground mounted
> array?   Or where is considered best placement for
> ground rods on
> ground-mounted arrays?   Ok, that's plural, two
> questions.  Pertinent NEC
> 2005 section would be great if anybody has that info
> handy otherwise.
>
> Thanks,
> Peter
> asappower.com
>
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