I'm a big fan of grounding at the array, and was sorry to lose 690.47D
(which also clearly allowed the structure to be considered an electrode) .
I think if you look at the sq ft. of metal in contact with the concrete,
you can make a credible case for the frame fitting the definition of an
electrode. IMHO, it's all about a low impedance path to ground. Whether
it's 20 ft of 1/2" rebar, or 4 ft of 6" diam pipe, or 4 ft of 2" x 2"
angle iron, its all roughly the same required 2 sq ft of surface area in
contact with the concrete.
Actually if you want to be a real stickler and also enforce 250.53A2, a
tough AHJ might demand 2 electrodes at the array in addition to the
structural grounding all ready present.
Me? I like the exception if the measured ground impedance is less than
25 ohm. Most inspectors will be more than satisfied, if you just show
them a quick reading with a clamp-on ground impedance tester.
What If you're still over 25 ohms? If you're in lightning country, you
really should sink another electrode anyway.
Ray
On 9/30/2011 7:04 PM, Kent Osterberg wrote:
Ray,
I believe that a pole-mounted or grounded-mounted PV array is
considered a structure and requires a ground electrode per 250.32.
Perhaps the exception would cover the possibility a installing very
small system without a ground electrode.
Kent Osterberg
Blue Mountain Solar, Inc.
Ray Walters wrote:
I've also used 250.52A(7) defining plate electrodes. A 6" Sch 40 pipe
4 ft in the ground has more than the required 2 sq ft of surface
metal, and is at least the required 1/4" thickness.
Also, the 2011 NEC dropped 690.47 D which required a grounding
electrode at the array. Are you sure you still need this? I believe
2011 only requires you bond all the metal to the EGC, as always.
Ray Walters
On 9/30/2011 8:24 AM, Kent Osterberg wrote:
The requirements listed in 250.52(3) were changed in 2011. The rebar
used is allowed to be near the bottom of the footing or in vertical
foundation walls that are in direct contact with earth. If there was
in doubt in the past that the rebar in the concrete of a pole mount
was a suitable grounding electrode, the changes in 2011 should
remove it.
Kent Osterberg
Blue Mountain Solar, Inc.
Richard L Ratico wrote:
As Dan points out, 250.52(A)(3) specifies several installation
requirements in
order for a concrete encased electode to qualify as a permitted
Grounding
Electrode. A pole mount foundation would certainly qualify if it
met those
requirements.
Even if the requirements are not met, IMHO, any opportunity to
inexpensively
increase the grounding integrity of a system should not be overlooked,
particularly in lightning country. Of course, a code compliant
Grounding
Electrode System is still required. Bonding a non compliant, but
never the less,
very substantial additional "electrode" to that system would not
hurt anything
and quite possibly help considerably.
Dick Ratico
Solarwind Electric
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