[RE-wrenches] ground

Ray Walters ray at solarray.com
Fri Sep 30 22:41:24 PDT 2011


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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