Grounding system for detached building question

[mach158]

I have a shop going up soon and I will be installing the service to it from my house panel. It will be a 100a panel.

The building will have a concrete floor with footings (the slab will have vapor barrier under it). I forgot to ask what size rebar will be used for the footing but if I understand correctly for the footing to be used as a UFER ground I need a minimum thickness of 1/2" correct?

Also, if the UFER ground will work I do not need additional grounding rods either, correct?

Then when tying into the rebar I understand I need 20' of continuous run of rebar or rebar connected via wire tie and I plan to stick the rebar above the concrete below the panel and make my connection there and that is acceptable as long as it does not count towards the 20'?

Final question, will I need to run #6 wire for the ground? I tried searching for all my answers and it seems most of the stuff mentioned early was consistent but the wire size seemed to range with #6 being the most consistent and I can't find where it will tell me the size I need.

 

[larry4406]

In the new houses I build in MD, we run 20' of #6 copper wire tied to the footing rebar. Then the copper continues up through the footing with sufficient length to connect directly to the panel ground. We do not leave the rebar exposed. We also do not pound in separate ground rods. The UFER is all there is.

When we build detached garages, the garage also has a UFER. Then 4-conductor wire from the house main panel to the detached garage sub panel. Detached garaged UFER wire connected to the detached garage panel ground which is separate from the neutral.

 

[Alchymist]

What Larry said.

 

[wyliesdiesels]

I have a shop going up soon and I will be installing the service to it from my house panel. It will be a 100a panel.

The building will have a concrete floor with footings (the slab will have vapor barrier under it). I forgot to ask what size rebar will be used for the footing but if I understand correctly for the footing to be used as a UFER ground I need a minimum thickness of 1/2" correct?

Also, if the UFER ground will work I do not need additional grounding rods either, correct?

Then when tying into the rebar I understand I need 20' of continuous run of rebar or rebar connected via wire tie and I plan to stick the rebar above the concrete below the panel and make my connection there and that is acceptable as long as it does not count towards the 20'?

Final question, will I need to run #6 wire for the ground? I tried searching for all my answers and it seems most of the stuff mentioned early was consistent but the wire size seemed to range with #6 being the most consistent and I can't find where it will tell me the size I need.

that wire is called a GEC grounding electrode conductor NOT a ground wire. The EGC aka ground wire goes from the main service panel to the garage subpanel.

In your subpanel, u need to make sure the neutral bar is isolated from the enclosure and EGC/ground bar. Some panels do not come with ground bars which can be purchased separately...

 

[Charles (in GA)]

Will the vapor barrier completely insulate the slab and footers from the earth? If so, the code says the concrete must be in direct contact with the earth..........

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.

(3) Concrete-Encased Electrode. A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either (1) or (2):
(1) One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (1⁄2 in.) in diameter, installed in
one continuous 6.0 m (20 ft) length, or if in multiple pieces connected together by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 6.0 m (20 ft) or greater length; or

(2) Bare copper conductor not smaller than 4 AWG Metallic components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.

Informational Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in “direct contact”
with the earth.

 

[mach158]

Will the vapor barrier completely insulate the slab and footers from the earth? If so, the code says the concrete must be in direct contact with the earth..........

It is my understanding the vapor barrier will just be under the slab.

wyliesdiesels - thanks for the correct terminology, I was not sure what to call it exactly as the terminology is not one of my strengths.

I am not familiar with tying into the rebar footing like I am connecting to the ground rods so a coupel more questions.

Do I tie to every piece of rebar in the 20' run of copper wire or only certain pieces of wire? As for the wire being used, should I be using bare copper wire or can I use stranded copper wire with a covering and then remove the covering for every piece of rebar I tie too?

 

[kingchevy]

When I built my house, I was told to bend a full piece of the footing rebar up so it would stick out of the slab and could be used as UFER. Recently while building my shop, my electrician friend told me that wasn't right because all 20 feet of the rebar was not in the ground. Instead he had me tie into a full 20 foot piece of rebar in the footing with an acorn and bring it out of the slab in a 1/2" conduit to protect it from physical damage during pour and construction. Made good sense to me.

 

[Aceman]

When I built my house, I was told to bend a full piece of the footing rebar up so it would stick out of the slab and could be used as UFER. Recently while building my shop, my electrician friend told me that wasn't right because all 20 feet of the rebar was not in the ground. Instead he had me tie into a full 20 foot piece of rebar in the footing with an acorn and bring it out of the slab in a 1/2" conduit to protect it from physical damage during pour and construction. Made good sense to me.

The code only requires that you have at LEAST 20' of minimum 1/2" bar in the footing which must be in direct contact with the earth. It is okay to have one piece of rebar or multiple pieces tie wired together to get this 20' minimum. Since all the footings I've seen have much more bar than that in them, it is not an issue to stub a piece of bar out of the concrete that is also tie wired to the other bar.

It is my understanding the vapor barrier will just be under the slab.

wyliesdiesels - thanks for the correct terminology, I was not sure what to call it exactly as the terminology is not one of my strengths.

I am not familiar with tying into the rebar footing like I am connecting to the ground rods so a coupel more questions.

Do I tie to every piece of rebar in the 20' run of copper wire or only certain pieces of wire? As for the wire being used, should I be using bare copper wire or can I use stranded copper wire with a covering and then remove the covering for every piece of rebar I tie too?

It's much simpler than that. Install your footing rebar like usual, make sure there is no vapor barrier under the footing. Now bend a 90 in a piece of bar long enough to stub up through the floor by at a least a few inches, so you can get a clamp on it. Tie wire this bar to the footing bar. Done. In Oregon the building inspector inspects the footings and puts a tag on this stubup which states it's approved as a ufer ground. The electrical inspector will then be looking for this tag when he does his inspection.