Ufer-ish ground - use or abandon

[matt_i]

So when I built my foundation (pad + stem wall 8" above grade) its built with rebar every 16" on center, both horizontally and vertically.

I left one vertical rebar nub, proud, by mistake, about 1/2" proud of the concrete, for lack of execution on my part.

Since then, looking at it, I said to myself I could make this into a ufer ground. I drilled and tapped the center of the vertical bar #10-24 and it has a corresponding hole sawed into the bottom wall plate for access.

Now its about time to close up the walls and I either need to finish this or abandon it.

I have in my mind I would buy a 100' piece of #6 bare copper (stranded) and land it on the bus bar of the 100A sub panel feeding the shop. Its all attached to the main residence and I ran a #2 THHN back to the main house panel so there's no additional grounding required.

Lightning strike protection would seem to be the thing to be after and I do have CNC machines with sensitive electronics plus digital phase converter, those would be the $$$$$ things I would want to protect. That said, I have never had a piece of equipment (PC, TV, router, or otherwise) damaged by lightining strike after living here 7 years.

Just curious about your thoughts as to whether I'm going to get the benefits I think I am by finishing this off? Is #6 enough to shunt lightning to ground or is it going to be balls of molten copper inside the walls?

 

[MEngineer]

Seems like a useful idea. I have heard of people grounding to their well casing if it is close to or within the structure. I cannot say if it is really needed, but I bet you would have a good ground assuming that you don't have foam under your slab for insulation

 

[matt_i]

Thanks, just to be clear (and I wasnt!) the pad footing and the stem walls are locked by the vertical rebar, horizontal rebar in both of those pours as well. The slab, while it has the same rebar @ 16" oc, is not locked to the walls; it floats inside. However the slab sits on a vapor barrier + 6" washed limestone, so I don't think the "water required for good conductivity" applies to the slab portion. Walls are 42" below grade minimum, 140-ish linear feet of poured wall that would be the useful, working part of the system.

 

[MEngineer]

I suppose a quick check you could do would be to run a hot wire over to that location and use a multimeter to verify that you have 120 ish volts differential from the hot leg to the rebar. If it is insulated and not grounded well, the one I have will throw an error code or something indicating no voltage potential.

 

[lakeroadster]

I did some research on ufer back when I built my barn because the 1st county inspector who looked at the footers made reference to it.

Ufer's were developed for use in very arid climates, where driving a ground rod down into dry soil isn't adequate.

If you use the rebar in your slab and footings and there is a lightening strike, it can damage the slab.

If I were in your location I would use the standard 2 ground rod set-up.

Ufer Ground

Ufer Grounds Blowing up Concrete

 

[Radix2]

How much rebar you really attached to? Just one of the 4 foot vertical pieces? If it is going to take 100' of copper to connect I would forget it. Drive your rods right next to the panel and connect there. Don't see the benefit of a 100' long path just looking for a place to arc to ground in case of a strike.

 

[larry_g]

When building my shop I asked the inspector and was informed that the ufer ground had to be inspected and marked BEFORE pouring concrete. One 20' length of rebar was not enough and it took a few lengths bonded together to make it long enough. I went with the two rods in the ground.

lg
no neat sig line

 

[prostreetamx]

Rebar uffers have to have at least 20ft embedded, encased in concrete near the bottom of your footing to be considered a grounding electrode. I wouldn't bother with what you have. My just built attached garage with 100a sub was required to have a separate uffer ground as well as the subfeed ground and a building ground in my case for the metal stud framing. Grounding codes have changed recently in Nevada due to the very dry soil. They also require 2 uffers separated by 8' on new construction.

 

[wyliesdiesels]

So when I built my foundation (pad + stem wall 8" above grade) its built with rebar every 16" on center, both horizontally and vertically.

I left one vertical rebar nub, proud, by mistake, about 1/2" proud of the concrete, for lack of execution on my part.

Since then, looking at it, I said to myself I could make this into a ufer ground. I drilled and tapped the center of the vertical bar #10-24 and it has a corresponding hole sawed into the bottom wall plate for access.

Now its about time to close up the walls and I either need to finish this or abandon it.

I have in my mind I would buy a 100' piece of #6 bare copper (stranded) and land it on the bus bar of the 100A sub panel feeding the shop. Its all attached to the main residence and I ran a #2 THHN back to the main house panel so there's no additional grounding required.

Lightning strike protection would seem to be the thing to be after and I do have CNC machines with sensitive electronics plus digital phase converter, those would be the $$$$$ things I would want to protect. That said, I have never had a piece of equipment (PC, TV, router, or otherwise) damaged by lightining strike after living here 7 years.

Just curious about your thoughts as to whether I'm going to get the benefits I think I am by finishing this off? Is #6 enough to shunt lightning to ground or is it going to be balls of molten copper inside the walls?

the one piec of pertinent info everyone missed is that its an attached structured. This means no additional grounding electrodes are required.

Just abandoned the thing, check off the item on your list, and move on to new projects.

BTW what is the breaker rating of the subpanel feeder? #2 THHN is robably overkill for the EGC...

I did some research on ufer back when I built my barn because the 1st county inspector who looked at the footers made reference to it.

Ufer's were developed for use in very arid climates, where driving a ground rod down into dry soil isn't adequate.

If you use the rebar in your slab and footings and there is a lightening strike, it can damage the slab.

If I were in your location I would use the standard 2 ground rod set-up.

Ufer Ground

Ufer Grounds Blowing up Concrete

This i hear is pretty rare and Ive only read about it once online. Never seen it happen before.

The UFER is superior to grounding rods and I believe that why the NEC requires no other electrodes when a UFER is used...

Rebar uffers have to have at least 20ft embedded, encased in concrete near the bottom of your footing to be considered a grounding electrode. I wouldn't bother with what you have. My just built attached garage with 100a sub was required to have a separate uffer ground as well as the subfeed ground and a building ground in my case for the metal stud framing. Grounding codes have changed recently in Nevada due to the very dry soil. They also require 2 uffers separated by 8' on new construction.

wow code out there has gotten crazy.

NEC doesnt require any kind of electrodes for attached structures....

 

[Dagny]

I think the best lightning protection is obtained by tying every piece of metal on your premise together with a conductor. lightning damages things when it jumps from one thing to another. Now getting concrete guys to do this will be very hard. Seems all brains fall out when a ready mix truck shows up.

 

[wyliesdiesels]

I think the best lightning protection is obtained by tying every piece of metal on your premise together with a conductor. lightning damages things when it jumps from one thing to another. Now getting concrete guys to do this will be very hard. Seems all brains fall out when a ready mix truck shows up.

Every piece of metal such as conduit, plumbing and building steel IS required to be bonded together and connected to electrical panel.

However without an electrode this wont do much good. There needs to be a path to earth for the lightning.

 

[lakeroadster]

If you use the rebar in your slab and footings and there is a lightening strike, it can damage the slab.

Ufer Grounds Blowing up Concrete

This i hear is pretty rare and Ive only read about it once online. Never seen it happen before.

The UFER is superior to grounding rods and I believe that why the NEC requires no other electrodes when a UFER is used...

Check out the link I provided. When it does happen it is because the rebar wasn't installed correctly... correctly to be used in an Ufer application. It's just like everything else in life, there's a right way... and a wrong way.

And yes it is superior.. in arid locations where the ground has very little moisture. It simply isn't needed in locations such as the OP's.

 

[matt_i]

Thanks for the comments, I think I will abandon it unless there's a spare piece of #6 THHN in my pile that I can strip back to bare and would be long enough to run to the top of the wall plate. Then I can at least shelve it until the next generation wonders what this damn bare wire is in the attic....