Grounding detached shop

[misterfixit]

building 30x40 workshop, concrete slab, metal 'frame' and metal siding.

My question is about grounding at the building. I'm trying to understand the correct way to run a ground rod through the slab under the service entrance for grounding. Does it have to be connected to the rebar in the slab? If it is connected to the rebar, do I still need the ground rod into the earth?

 

[misterfixit]

And I forgot to mention this is out in the county there is no inspection, meaning there is no one to inspect it, no requirement, no inspector exists.

 

[u2slow]

Ground rods are usually driven into the ground outside the building. Wire is run through the wall and into the panel.

 

[sberry]

If there is a footer it needs to be connected to resteel in the footer, a couple rods worth I believe but then it doesn't require rods.

 

[misterfixit]

If there is a footer it needs to be connected to resteel in the footer, a couple rods worth I believe but then it doesn't require rods.

What do you mean a footer?

 

[u2slow]

What do you mean a footer?

Its the base of your concrete stem wall in standard construction, and the slab is poured later.

I suspect you have a monolithic slab, so it doesn't apply.

 

[wyliesdiesels]

If you do a UFER electride which is aka concrete encase electrode then you dont need ground rods.

Make sure to bond any metallic plumbing such as water and gas.

 

[misterfixit]

If you do a UFER electride which is aka concrete encase electrode then you dont need ground rods.

Make sure to bond any metallic plumbing such as water and gas.

What is the requirement for the wire size or type between the panel and ufer

 

[dscheidt]

What is the requirement for the wire size or type between the panel and ufer

Depends on the ampacity of the service, and the size of the wire used. There's a table (250.122) in the code book. If the wire size of the supply are increased from the minimum required, the grounding conductor has to be increased as well.

 

[misterfixit]

looks like the ground connector wire is 4 awg.

 

[spudley]

Good thing to plan ahead.

Wish I would've done a UFER ground stub inside below my panel, but I wasn't dead set on panel location so that wasn't a viable option.

Oh well, now I get to punch another hole in the siding.

Absent a UFER, we're required to install two 8' rods minimum 6' apart.

 

[misterfixit]

Good thing to plan ahead.

Wish I would've done a UFER ground stub inside below my panel, but I wasn't dead set on panel location so that wasn't a viable option.

Oh well, now I get to punch another hole in the siding.

Absent a UFER, we're required to install two 8' rods minimum 6' apart.

My slab will have a 12x12 perimeter beam, I'm putting #4 rebar in it. I'll use that as an Ufer.

Where I'm at, out in the county outside of any city limits, there are no permits or inspections. That makes it easy for folks who want to cut corners, but at the same time makes it (at least to me) a bit tougher for those who want to do it right because there is no clear directions on what is required. There is no standard, no inspector to call and ask what they accept. SO, absent clear directions and regulations, I'll be running 4 wire to the shop, and using the #4 rebar (140 feet worth) as an Ufer, sticking a few inches of rebar up through the slab under the area the breaker panel will be, and connecting with a 4awg wire.

Unless someone has a good reason not to do it that way.

 

[vtjon]

My slab will have a 12x12 perimeter beam, I'm putting #4 rebar in it. I'll use that as an Ufer.

Where I'm at, out in the county outside of any city limits, there are no permits or inspections. That makes it easy for folks who want to cut corners, but at the same time makes it (at least to me) a bit tougher for those who want to do it right because there is no clear directions on what is required. There is no standard, no inspector to call and ask what they accept. SO, absent clear directions and regulations, I'll be running 4 wire to the shop, and using the #4 rebar (140 feet worth) as an Ufer, sticking a few inches of rebar up through the slab under the area the breaker panel will be, and connecting with a 4awg wire.

Unless someone has a good reason not to do it that way.

I am building a garage (permitted) and I just had my electric rough-in inspection for 200amp dedicated service. I have an Ufer (I have a basement walls but I believe it's a minimum of 20ft of continuous (tied) rebar which sounds like you have. I had close to 3ft sticking up for my Ufer but I cut it back to about 18 inches. It's my understanding you can't hide your ground clamp, not sure if that's concern for you. I used 4 AWG stranded THHN wire. It is much easier to run than solid copper.

 

[dcg9381]

If you do a UFER electride which is aka concrete encase electrode then you dont need ground rods.

Make sure to bond any metallic plumbing such as water and gas.

This is what the electrician did on the slab to my home. Looks like a copper wire comping up (encased in flex conduit)... In my area, this is a LOT easier than driving a 8' ground rod into rock..

 

[wyliesdiesels]

Depends on the ampacity of the service, and the size of the wire used. There's a table (250.122) in the code book. If the wire size of the supply are increased from the minimum required, the grounding conductor has to be increased as well.

Wrong table. That is for the EGC/ ground wire for fault current.

GEC for electrodes is sized with table 250.66

 

[dscheidt]

Wrong table. That is for the EGC/ ground wire for fault current.

GEC for electrodes is sized with table 250.66

oops. Should have checked. I can never remember table numbers.