Additional Electrodes for Array Grounidng 690.46(D) and 250.52

I need some clarification on section 690.46(D). It says that the stucture of a ground or pole mounted PV array shall be permitted to be considered a grounding electrode if it meets the requirements of 250.52. When reviewing 250.52 (Grounding Electrodes) (A) Electrodes Permitted for Grounding - (2) Metal Frame of Building or Structure - the metal frame of the building or structure that is connected to the earth by any of the following methods: (1) 3.0 m (10 ft) or more of a single structural metal member in direct contact with the earth or encased in concrete that is in direct contact with the earth.

Does this all mean that the pole used for a solar top-of-pole installation is the structure and does the pole have to be 10 feet or longer and buried in concrete or does it mean it has to be buried in the ground 10 feet with concrete to use the pole as the grounding electrode?

I have seen an a couple of Top-of-Pole installations where they have used the pole as the grounding electrode. The poles (6 inch sched 40) were 8 feet in the ground with 1 1/2 yard of concrete, and13 feet in the air. No ground rod used or any tie to rebar in the footing concrete with the grounding conductor that was only connected to the pole via a lug and at the combiner ground lug..




  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Additional Electrodes for Array Grounidng 690.46(D) and 250.52

    i take it to mean in the ground 10ft with or without the concrete regardless of how much is above the ground. by this i take it as 8ft does not qualify and should have a proper 10ft ground rod driven into the ground and the pole structure attached to it. this is to try and establish at least a certain amount of contact area with the ground. i know the large diameter of the pipe does provide extra contact area with the ground compared to the standard 10ft ground rod and there may be a provision somewhere in the nec rules about this, but i can't say for sure. i look at the ground rod as extra insurance and would do it anyway as i do not believe concrete to be low enough resistance compared to the surrounding earth imho even though the nec has allowed it.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Additional Electrodes for Array Grounidng 690.46(D) and 250.52

    In my new office/workshop the ground attachment to the monolithic slab rebar was acceptable to the code guys. I thought for sure they would have wanted the ground run back to the main panel ground location which is attached to both a rod and the water service entrance. Of course when doing service entrance upgrade from 200 amp to 400 amp, the ground wire size was required to increase. I think the new 200 amp sub panel with a 125 amp breaker is now attached to both locations, the main panel and the slab.

    I thought that was a no no.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Additional Electrodes for Array Grounidng 690.46(D) and 250.52

    It is a bit sticky. Driving a manufacturered ground rod at the array is usually the only code compliant way to go.

    I think Niel is right about the 10' issue. If it were just a pipe with no concrete it could be 8'. You could make a UFER ground with 20' of bare # 4 incased in the footing.

    There is;
    NEC 250.52(A)(5) Ground Rod and Pipe Electrode.

    Electrodes of pipe or conduit of iron or steel must be galvanized or otherwise metal-coated for corrosion protection and must not be less than 8 ft in length in contact with the earth. But since the pole is concrete encased (NEC 250.52(A)(3)) it needs to be 10' burried.

    There is also a note for 2011 that says concrete is not in direct contact if it is lined with a vapor barrier or similar flim.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Additional Electrodes for Array Grounidng 690.46(D) and 250.52

    actually, i stand corrected as i stated with or without concrete, but you clarified it to be 10ft with concrete only and 8ft otherwise. sounds more like i remembered. what month is this now?:confused:

    anyway, the nec does not require a ground rod at the pvs as they only require the ground wire connection to travel back with the pv leads into the house where it eventually goes through all the grounds there and to your utility service entrance breaker box and from there it goes to the required ground rod for your utility electric. kinda bass ackwards and dangerous imho.
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