Grounding electrode placement on landfill

[adunbar]

We are installing an electrical system on a landfill and need to install a grounding electrode. The landfill is capped and has only 12" of soil fill above the cap. We are proposing using a ground plate and adding 30" of fill in the 3' square area above the plate to satisfy the cover requirements per code. We would need to run wire 600 ft to get off the landfill to attach to a ground rod.

Please comment if you think this will be acceptable to an AHJ.

 

[ceb58]

Please comment if you think this will be acceptable to an AHJ.

He is the one to ask this question. Just follow 250.52 (7), 250.53 (A) and 250.56

 

[petersonra]

My question.

How is the power getting there from so far away? If it is buried, it is not deep enough if it is only 12 inches down. If it is on poles, the poles are going to have to be deeper than that.

 

[Cow]

I had the same question as Bob^^.

 

[Dennis Alwon]

If this is a new building I would add a CEE if not then perhaps you would need to drive longer rods.

 

[adunbar]

We are building a PV system on the landfill. The primary wiring will come from the road encased in concrete. We are constructing a pad on the landfill for our inverters, transformers, CT cabinets etc where the primary will land. This pad will have a ground ring and grounding plates.

I am concerned about grounding at the PV arrays. There could be over 400 feet between the panels and inverter and I want to provide local grounding electrodes at several points within the array.

The landfill only has 6" of soil above it's PVC cap and we can not penetrate this cap. The code gives a minimum cover for ground plates of 30" but we don't typically have 30" of soil unless we mound it above the plate.

We do have 12' concrete ballast blocks with rebar sitting on the ground that could perhaps be looked at as a U-fer ground.

Any suggestions for this local grounding?

 

[petersonra]

We are building a PV system on the landfill. The primary wiring will come from the road encased in concrete. We are constructing a pad on the landfill for our inverters, transformers, CT cabinets etc where the primary will land. This pad will have a ground ring and grounding plates.

Why both?
I am concerned about grounding at the PV arrays. There could be over 400 feet between the panels and inverter and I want to provide local grounding electrodes at several points within the array.
Why do you want to ground the PV arrays? Is there some non-obvious benefit to doing so?
The landfill only has 6" of soil above it's PVC cap and we can not penetrate this cap. The code gives a minimum cover for ground plates of 30" but we don't typically have 30" of soil unless we mound it above the plate.
So mound it. It is just dirt.
We do have 12' concrete ballast blocks with rebar sitting on the ground that could perhaps be looked at as a U-fer ground.
They may well be a perfectly good means of grounding but I don't know that they meet the requirements for a GE. OTOH, if you are talking about ballast blocks for the PV arrays I don't know that they require a GES anyway so feel free to connect right up.
Any suggestions for this local grounding?

Mounding dirt on top of something is ugly but it is a landfill. Who cares?

I question how effective any GES is when installed above a PVC cap.

 

[Cow]

Eventually, you just gotta ask the question:

Why not put the array somewhere else where it's not on top of a pvc cap if you're so worried about installing supplemental grounding electrodes?

 

[kwired]

Even if you piled up dirt on top of the PVC cap I question whether you will improve conductivity by any significant amount. If you only have 6 inches of dirt and in an area that does not receive a lot of rain that soil will be pretty dry making your electrode almost as effective as leaving it lay on top of the soil.

 

[tom baker]

A plate electrode has the worst, or highest resistance of any electrode. Run a bare 4 AWG in the concrete for the duct bank and hit two ground rods at the real dirt. the 4 AWG in the concrete will have a very low resistance.

 

[adunbar]

Please let me know if you would still recommend using a #4 bare wire run in concrete with our primary wiring knowing that this run is about 600 feet to get off the landfill to allow installing ground rods. We felt this was not the lowest impedance path. That is why we are calling for a ground ring and ground plates.

Could we instead connect to the rebar in the 50' x 40' concrete equipment pad as our GEC and assume this was the lowest resistance path? The pad is at the center of the array.

The rebar in the ballast blocks throughout the array could then be used as supplemental grounding.

Reusing the landfill for a PV system is a good use of wasted land We just need to figure out how to do it safety.