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Electrical ground in shallow bedrock

1110d's picture

I have a cabin in Northern Wisconsin that I've been building for 7 years.  The project is to the point of electrical rough.  So far I've done all the work legally having pulled the necessary permits and requesting the inspections.  I'm happy to say that I've never failed an inspection and I'd like to continue that pattern for the electrical work.  That said, the inspector has declined to issue an electrical permit because the home is off grid.  Electric stops 1/4 mile down the road and, due to high bedrock, the utility has quoted me $40,000 to bring in the primary.  That's beyond my means which is why it's off grid.  

I know from when I set the footings the bedrock is 2-50" deep.  I think the average depth would be in the 9-12" range.  I know the 50" spot was a fluke because the footing 4' away was only 20" down.  From what I've seen, the bedrock appears to be pockmarked and not a flat "ledge".  I had 2x2 piers with 16" of elevation change in the hole.  Thankfully I didn't need to form for footings and I just poured the pier excavation solid.

When it comes to the panel ground, I know I won't be able to drive two ground rods.  Maybe I'll get lucky with one and find a fissure, but not two.  It's my understanding that the code has provisions for this situation and permits the ground rods to be placed horizontally or for plates to be used.  The problem is the 30" minimum cover.  I think there may be a chance to provide 30" of cover to the plate, but if I'm short?  Are there any provisions for less than 30" of cover?

Again, I know the inspector has declined to issue a permit, but I see that as no reason why I can't have a safe, code compliant installation.

In general, if electrical (post #214971, reply #1 of 5)

In general, if electrical lines cannot be buried to spec depth it is permissible to protect them with some sort of cover -- I'm thinking a layer of concrete, though it's been about 20 years since I read the code book on this point.

I'm not sure if this detail in the code applies to grounding electrodes, though.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

UFER (post #214971, reply #2 of 5)

It may be too late, but the required and acceptable ground means for quite some time has been a UFER. A full 20' length of the bottom rebar in your footings is bent up out of the concrete enough to attach a ground clamp. To repeat it needs to be the bottom bar and a full 20' long. It should have been done before the concrete was poured. Other than two ground rods I know of no acceptable retro fit.  But, given that you are off the grid, you should think about using all 12v DC. You can use it for lighting and electronics, everything but refrigeration. 

There are 24v freezer / (post #214971, reply #3 of 5)

There are 24v freezer / refridgerator systems available, specifically designed for off-grid residential use.

Can you get 30"? (post #214971, reply #4 of 5)

I would try probing around somewhere near your proposed electric looking for a 30" deep spot and laying a plate electrode on the rock. The Ufer was probably your best option but that is in your rear view mirror. If you are not connecting to the grid the ground may not really be that critical but you still need one by code. At some time in the futrure that power may get down to you, depending on who your neighbors are


Retrofit. (post #214971, reply #5 of 5)

It is approved to retrofit 2 wire systems with grounding recepticals if they are put on a GFIC. You could ground fault the entire building. It might not be legal but it would be safe.