Auxilliary electrodes for array grounding

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WhiteB

New member
Location
Syracuse, NY
It is common for us to install arrays on top of old landfills. The specifications for every one of these projects we have worked on prohibits us from digging or penetrating the soil. Article 690.47(D) states that we 'shall install a grounding electrode at all ground mounted arrays'. The arrays themselves are mounted to ballast blocks, and all wiring is done with cable tray. How do we comply with this section of the code when we are not allowed to penetrate the ground?
 

Smart $

Esteemed Member
Location
Ohio
Welcome to the forum, WhiteB. :thumbsup:

Where the NEC is adopted by law (which I believe it is in NY), it will supersede any job spec' which lowers property and life safety. You should verify in writing with AHJ and RFI the pertinent parties both to serve as notice and to obtain the particulars of implementation.

If ground penetration is also prohibited by law, the AHJ will have to figure it out... :happyyes:
 

SolarPro

Senior Member
Location
Austin, TX
Good question.

You might look ahead at the proposed NEC 2017 language and see if the AHJ will let you apply the "most recent" code requirements. As you are likely aware, the requirements in 690.47(D) basically come and go on a 3 year interval. I believe the 2017 Code will basically say that auxiliary electrodes are allowed, which is very different than saying they are required.

Otherwise, you'd have to do something like a built up ground ring, similar to what you are doing at your equipment pad. Since auxiliary grounding electrodes are not required to be built to the same standard as a [real] grounding electrode, you might be able to argue that the normal cover requirements for a ground ring need not apply in the array field. Kind of weird, but no weirder than mandating a grounding electrode that is not a grounding electrode, which is basically what 690.47(D) does in NEC 2014.
 

Carultch

Senior Member
Location
Massachusetts
It is common for us to install arrays on top of old landfills. The specifications for every one of these projects we have worked on prohibits us from digging or penetrating the soil. Article 690.47(D) states that we 'shall install a grounding electrode at all ground mounted arrays'. The arrays themselves are mounted to ballast blocks, and all wiring is done with cable tray. How do we comply with this section of the code when we are not allowed to penetrate the ground?


690.47(D) is a contentious part of the NEC that Mike Holt claims can be counterproductive to safety. Not in the application of most ground-mount systems, but in most building systems.

See this discussion, and see if you can make a case to not be required to use 690.47(D)anger.
https://www.youtube.com/watch?v=YuDqXFvRv94

Alternatively, is there any section of land on the project that you are allowed to penetrate? I'm picturing a slab that is not part of the capped landfill, where you'd likely place your transformer, master switch, and other large equipment.
 

SolarPro

Senior Member
Location
Austin, TX
That was my first thought as well. Ideally, the ground ring at the equipment slab can suffice to meet 690.47(D). Your slab and the base it is built up on can meet the ground ring cover requirements. If that equipment is located within the array field, which is typical of the landfill projects I've looked at, then you may not need any auxiliary electrodes at all.
 

david

Senior Member
Location
Pennsylvania
It is common for us to install arrays on top of old landfills. The specifications for every one of these projects we have worked on prohibits us from digging or penetrating the soil. Article 690.47(D) states that we 'shall install a grounding electrode at all ground mounted arrays'. The arrays themselves are mounted to ballast blocks, and all wiring is done with cable tray. How do we comply with this section of the code when we are not allowed to penetrate the ground?

What is the solar power supplying?

why not just use exception # 2 is there some reason it would not be practical to land the grounding electrode conductor to the grounding electrode (s) at the site.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What is the solar power supplying?
In this case as in all grid tied solar, the load supplied by the PV system is the grid. The local loads, if there are any, are part of the grid from the perspective of the inverter. In this case, which sounds like a utility scale project, there most likely are no local loads.
 

69gp

Senior Member
Location
MA
It is common for us to install arrays on top of old landfills. The specifications for every one of these projects we have worked on prohibits us from digging or penetrating the soil. Article 690.47(D) states that we 'shall install a grounding electrode at all ground mounted arrays'. The arrays themselves are mounted to ballast blocks, and all wiring is done with cable tray. How do we comply with this section of the code when we are not allowed to penetrate the ground?
.

Please see the link below. This is typical of how the aux.ground is done on solar arrays in MA for landfills. Depending on deep the landfill cap is will dictate how deep to bury the ground plate.


http://www.tlpinc.com/products/grounding/ground-plates.html
 

69gp

Senior Member
Location
MA
If you can't raise the bridge, lower the river :).

Why not lay down a ground plate or rods and dump a few cubic yards of dirt over it? You haven't penetrated the existing soil but now have a buried electrode.


ground plates are the way to go.
 

david

Senior Member
Location
Pennsylvania
In this case as in all grid tied solar, the load supplied by the PV system is the grid. The local loads, if there are any, are part of the grid from the perspective of the inverter. In this case, which sounds like a utility scale project, there most likely are no local loads.

ok, some of our land fills have scale houses with some local loads
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
ok, some of our land fills have scale houses with some local loads
It makes no difference to the inverter if there are loads on the customer's side of the meter. It's all just the grid.
 

david

Senior Member
Location
Pennsylvania
What is the solar power supplying?

In this case as in all grid tied solar, the load supplied by the PV system is the grid. The local loads, if there are any, are part of the grid from the perspective of the inverter. In this case, which sounds like a utility scale project, there most likely are no local loads.

here i talked to the solar guys about that yes that may be true, but the utility is taxing the consumer, rather the utility is taxed generating fees and the utility is charging the consumer there portion of fees for what they generated onto the grid. They say for that reason they are trying to design their solar to not exceed consumer consumption
 

69gp

Senior Member
Location
MA
Just that under the NEC those scale houses need to have a fully compliant GES. So how do they do it?


An example would be as follows.

Say that town ABC has a 30 acre capped landfill site. Of that 30 acres only 22 acres may have been used to place the debris. That leaves 8 acres that there would be no membrane underneath it. You could drive rods here set poles and it would have no effect on the cap at all. Most landfill need to be closed for several years before you can put a system on them. This is do to settling of the site. We do work at several landfills and they do have surveyors come in and use a GPS to check the settling.
 

david

Senior Member
Location
Pennsylvania
It makes no difference to the inverter if there are loads on the customer's side of the meter. It's all just the grid.

Just that under the NEC those scale houses need to have a fully compliant GES. So how do they do it?

A that was my point if the scale house has even min. loads you would think it would be close enough to the solar to benefit from the solar power . It is a structure that would be required a grounding electrode system

we all understated that an existing grounding electrode system may not be available, there may not be a scale house or some other existing structure
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
here i talked to the solar guys about that yes that may be true, but the utility is taxing the consumer, rather the utility is taxed generating fees and the utility is charging the consumer there portion of fees for what they generated onto the grid. They say for that reason they are trying to design their solar to not exceed consumer consumption
Apples and oranges. Different AHJ's have different policies regarding PV production vs. consumption on residential systems and others regarding commercial systems, but a ground mounted PV system on a landfill is most likely to be a utility scale system. In those systems consumption isn't a significant part of the picture. They exist for the sole purpose of selling energy to the utility.
 
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