? regarding service entrance grounding electrodes

[EightFingers]

How many are required if you're on solid rock? How deep?
I didn't want to hijack the other post about electrical....

[Wao nahele kane]

I'm not certain with regard to your question although there is an alternative if you happen to be setting up a foundation. You can ground to the rebar inside the foundation before its poured and if possible, it's the best grounding method available.

Edit to add following link:
http://ecmweb.com/mag/electric_achieving...le_ground/


E ho'a'o no i pau kuhihewa.

[EightFingers]

We'll have a steel house on post and pier. We do have areas of fairly deep soil, but we plan on biulding our house on what's more or less solid rock. With PVC plumbing, grounding electrodes are the only way to achieve a ground AFAIK.
Losing the ground can have some pretty bad consequences. The inspectors are supposed to check this, but the final responsibility of the house is still up to me

[Royall]

I'm on rock. I was required to have 2, 8' rods at the temporary/determinant pole with in so many feet of each other. Two more at the house where the power enters, and yet two more at the point where the power enters the garage! The 2 at the power pole were easy to do. The company that drilled the holes in the blue rock for the pole also drilled the ground rod holes. Never would have gotten them in other wise. Rods at the house and garage were another story. Start pounding and hope you find a crack in the rock or pay to have more holes drilled. Also be sure you install the required diameter ground rod.

Royall

BTW... If you are building on slabs you can tie into the re-bar for your grounding be sure to have that part inspected before you pure though or hope they accept photos!

[Wao nahele kane]

Though they (inspectors) may accept grounding through ground rods in solid lava... I wouldn't accept it for my house. I'd establish a vast amount of surface contact with Lava in order to establish enough conductance to Earth ground. As Royal and myself have pointed out, the rebar in your foundation, rafting pad (if used) and or even a steel bar and or steel mesh re-enforced driveway pad will establish a vast permanent conductive surface contact with the lava and the concrete will conduct electricity from the rebar to the lava. Concrete does coduct electricity mostly due to it's moisture absorbtion qualities and the mineral content of the mix, so, if you can imagine all that steel surface area tied together and then properly clamped to a copper grounding conductor imbeded in concrete that uses a large surface area contacting the poor conductive lava, then you have a good reliable ground extablished with solid bonds at all the conductive surface areas. Anyhow.. that's how I planned to have our ground established as we have very little soil and none of it is deeper than a foot at best. To get even better results you can have a small amount of soils (just enough to fill the voids) brought in to mix with the substrate you place under your driveway or rafting pad.
Just a thought to avoid having to pay a crew to come in and drill holes that might not be reliable.

E ho'a'o no i pau kuhihewa.

[Seeb]

How about an out there idea for an Actual ground in a rocky area - " In the leach field "

[jerry]

Your choices are:

20' of #4 copper in the bottom of the slab (called a ufer)
#6 copper connected to a 20' piece of re-bar in the bottom of the slab
2 ground rods, spaced more than 6' apart, either driven or buried in a 24" trench.

It used to be common practice at meter poles to have the people drilling the holes for the meter pole drill holes for the ground rods, insert the rods and fill with concrete. Inspectors are no longer accepting this. The code says the ground rods must be "in contact with soil" and concrete is not soil. (The choices in the slab are considered "concrete encased electrodes," not the same as driven ground rods.) So you need to drill the holes, fill with soil, then drive the ground rod. I have a special order 7' long bit I use for this operation, but prefer concrete encased electrodes whenever possible.

Jerry

[Wao nahele kane]

Jerry,
A couple questions.
Does the inspector test the resistance between the two ground rods or do they simply "ass""u""me" it meets current standard?
Is this "in contact with soil" from the NEC or from the former CoH code; because as far as the NEC should be concerned and if used to describe contact with the electrode it has a far more reaching meaning. If its CoH defined it’s probably just as arbitrarily disjointed as the majority of the rest of its codes.
From the Army Corps of Engineering and all other legitimate sources, Soil is a term used to describe the composition of the Earth that is not composed of a majority concentration H2O. Granite, Basalt, Lava, Clay and or Dirt are all just a few of the several forms of “Soil” thus soil is not solely used to describe Dirt though commonly confused as such. Technically speaking and though this may appear very strange: concrete is a product composed of soil and though not widely naturally occurring and rare as it may be in nature, it’s a naturally occurring soil also, just as glass is.
So the meaning of soil is diverse and I cannot believe that the NEC would not pay heed to establishing a given power load capacity that must be met, vs. mandating 2 mandatory ground rods in an arbitrary material, it simply seems a very irresponsibly formed code and not at all in the spirit of the NEC and more liken to some crazy wayward CoH code.
If it is NEC, then there has to be far more content in the subject.


E ho'a'o no i pau kuhihewa.

[Wao nahele kane]

Eightfingers,
There is one other thing that will alter grounding requirements... Are you offgrid or using county provided electricity and if using county electricity are you also using an alternative energy source such as wind or solar? If you're using both you'll need seperate grounds for each source type. Royall... do you have a Solar PV system and county power both? If so, that's why you had to have a couple distanced grounding points to avoid ground looping between the differing systems.

E ho'a'o no i pau kuhihewa.

[EightFingers]

Wao nahele kane, we will have a have a hybrid system (solar/wind/backup genset) and I understand about the need for seperate grounds.
I'm wondering if the electrical inspector will actually "ohm out" the installation. Another thing I wonder about is dry vs wet periods. I think I could possibly lose my ground as the(what little I may have) soil dries out.
I had also thought about drilling a larger hole and using concrete as a filler, but you all beat me to that.
Outbuildings (we will have at least two) will also have to have their own grounding systems. Gonna have a lot of holes drilled!
Royall, you were brave to try just pounding them in!