Grounding rod suggestions......

[Ihateclevernames]

Gents, so I am in a bit of a time crunch here as my concrete guy moved my timeline up a week.

I currently have the building done and the subpanel box hung, with an LB on the exterior that will be used to feed my 3 gauge wire from the house.

Anywho, I will carry the ground from the house into the box, however I need to figure out the grounding rod issue for the box itself.

It is my understanding that I will need 2 ground rods for the panel box, however I need to figure out how far apart they have to be. In order to keep everything neat, I would like to keep them on the interior of the building.

I doubt that I will be able to put them under the slab as I won't have time for the inspector to come out and take a look at them prior to the pour on Wednesday.

So I am thinking that I either have to put the ground rods on the exterior or leave some sort of access on the interior. If I were to put them on the interior, I could place a piece of PVC pipe on the floor in order to be used as a form with access to the ground in order to insert the ground rods and then concrete the interior of the PVC forms later on after the inspector has had a chance to take a look.

If I go with the other, and have to put the on the exterior, I only worry about having to punch more holes in the walls whilst keeping things neat and orderly. Being that the exterior is only gravel, I also worry about wires getting snagged on things and potentially running over the rods with lawn equipment.

Thanks in advance!

 

[ishiboo]

1) I would put them outside, I've never heard of them buried under a slab. They can be buried outside - just leave the top connections exposed until the inspector leaves. (It's legal to have them covered, they'll just want to see the connections)

2) Speaking of concrete, are you sure a UFER is not required?

 

[Ihateclevernames]

1) I would put them outside, I've never heard of them buried under a slab. They can be buried outside - just leave the top connections exposed until the inspector leaves. (It's legal to have them covered, they'll just want to see the connections)

2) Speaking of concrete, are you sure a UFER is not required?

So would I just run them back out of another LB from the box into the ground with schedule 40 and then drive them into the ground appropriately?

 

[CNGsaves]

Gents, so I am in a bit of a time crunch here as my concrete guy moved my timeline up a week.

I currently have the building done and the subpanel box hung, with an LB on the exterior that will be used to feed my 3 gauge wire from the house.

Anywho, I will carry the ground from the house into the box, however I need to figure out the grounding rod issue for the box itself.

It is my understanding that I will need 2 ground rods for the panel box, however I need to figure out how far apart they have to be. In order to keep everything neat, I would like to keep them (ie 2 ground rods) on the interior of the building.

I doubt that I will be able to put them under the slab as I won't have time for the inspector to come out and take a look at them prior to the pour on Wednesday.

So I am thinking that I either have to put the ground rods on the exterior or leave some sort of access on the interior. If I were to put them on the interior, I could place a piece of PVC pipe on the floor in order to be used as a form with access to the ground in order to insert the ground rods and then concrete the interior of the PVC forms later on after the inspector has had a chance to take a look.

If I go with the other, and have to put the on the exterior, I only worry about having to punch more holes in the walls whilst keeping things neat and orderly. Being that the exterior is only gravel, I also worry about wires getting snagged on things and potentially running over the rods with lawn equipment.

Thanks in advance!

You're NOT understanding grounding of subpanel.

It's EITHER . . .
. . . . . a) UFER ground built into the footings/slab with rebar connected
. . OR . .
. . . . . b) 2 grounds rods OUTSIDE driven into dirt at least 6 ft apart
(connected with continuous copper wire . . . IIRC 6 gauge)

GJ Sparkies will chime in soon and give you all the details.

 

[wyliesdiesels]

OP- do u have footings or is it just a slab?

If u do have footings, did u put in a UFER ground?

What u can do is run a solid #6 cu wire back out the building through the LB and connect it to 2 rods spaced 6' apart.

U said u have #3 wire from the house. Did u run 3 or 4 wires from the house? Hopefully 4 wires as an EGC is now required(since 2008 code cycle) for detached buildings.

 

[Ihateclevernames]

OP- do u have footings or is it just a slab?

If u do have footings, did u put in a UFER ground?

What u can do is run a solid #6 cu wire back out the building through the LB and connect it to 2 rods spaced 6' apart.

U said u have #3 wire from the house. Did u run 3 or 4 wires from the house? Hopefully 4 wires as an EGC is now required(since 2008 code cycle) for detached buildings.

Still haven't ran those. That is happening this weekend.

The plan was to run 4 wires.

You guys are right, I did not understand the way to ground the subpanel box on the interior of the building. I will just go with running the grounding wire outside the building and then grounding appropriately.

I am assuming that I can run a single wire from the box, connecting both grounding rods?

 

[malibu101]

You're NOT understanding grounding of subpanel.

It's EITHER . . .
. . . . . a) UFER ground built into the footings/slab with rebar connected
. . OR . .
. . . . . b) 2 grounds rods OUTSIDE driven into dirt at least 6 ft apart
(connected with continuous copper wire . . . IIRC 6 gauge)

GJ Sparkies will chime in soon and give you all the details.

I am NOT trying to pick this quote apart. I am simply wondering this.....
Assume I have a building with concrete footings and floor with a proper UFER ground attached to the rebar.
Assume I am the grounding king and I also want to run 2 ground rods outside in addition to the UFER because I like overgrounding.

Can't I? Must I choose one over another and cannot use both?
Again, just wondering why not? What can it hurt? Just like in a house main that the metallic water main must be grounded AND have ground rods that's 2 grounds like I'm asking about.

 

[DC73]

I am NOT trying to pick this quote apart. I am simply wondering this.....
Assume I have a building with concrete footings and floor with a proper UFER ground attached to the rebar.
Assume I am the grounding king and I also want to run 2 ground rods outside in addition to the UFER because I like overgrounding.

Can't I? Must I choose one over another and cannot use both?
Again, just wondering why not? What can it hurt? Just like in a house main that the metallic water main must be grounded AND have ground rods that's 2 grounds like I'm asking about.

Local inspector required me to have 1 UFER ground and 1 external ground rod. No reason you can't have two.

DC

 

[Speedy Petey]

You're NOT understanding grounding of subpanel.

It's EITHER . . .
. . . . . a) UFER ground built into the footings/slab with rebar connected
. . OR . .
. . . . . b) 2 grounds rods OUTSIDE driven into dirt at least 6 ft apart
(connected with continuous copper wire . . . IIRC 6 gauge)

GJ Sparkies will chime in soon and give you all the details.

This is not at all true.

First off, if there is rebar in the footings, under recent codes you MUST use this for a CEE (Ufer) since it is present. In that case NO other electrodes are required.
Also, it is definitely NOT one or the other, nor are ground rods required. There are several other methods of grounding electrode, although rods are typcially easiest and most common.

 

[Speedy Petey]

Local inspector required me to have 1 UFER ground and 1 external ground rod. No reason you can't have two.

DC

Then unless there is a written amendment in your area your inspector does not know the code.

If a CEE (Ufer) is used NO other supplemental electrodes are required. None. The Ufer alone is sufficient.

 

[Speedy Petey]

I am NOT trying to pick this quote apart. I am simply wondering this.....
Assume I have a building with concrete footings and floor with a proper UFER ground attached to the rebar.
Assume I am the grounding king and I also want to run 2 ground rods outside in addition to the UFER because I like overgrounding.

Can't I? Must I choose one over another and cannot use both?
Again, just wondering why not? What can it hurt? Just like in a house main that the metallic water main must be grounded AND have ground rods that's 2 grounds like I'm asking about.

The quote you posted is wrong (see my previous reply). It is definitely NOT one or the other.

Once code minimum is met you can have as much extra as you want.
Although other than for something like a radio antenna or tower you are wasting money, but it's your money to waste.
Grounding electrodes do very little in most cases.

 

[CNGsaves]

^ ^ ^ See . . . I knew GJ Sparkies would chime in with details . . . .

But sure sounds like detached garage ends up being UFER . . or . . 2 ground rods.

If OP had concrete guy and electrician all on the same page, he would have had UFER all planned out (ahead of time) and not need to worry about . . MORE . . . grounding with rods !!

 

[Speedy Petey]

But sure sounds like detached garage ends up being UFER . . or . . 2 ground rods.

What do you base this on?

Code clearly states if rebar exists and meets certain conditions it MUST be used. Code also clearly does not require any other electrodes if a Ufer is used.
Would you like the NEC text?

 

[Speedy Petey]

250.50 Grounding Electrode System

All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.


(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 (½ 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.

Rod, pipe and plate electrodes all require supplemental electrodes. CEE's do not. This is in "250.53 Grounding Electrode System Installation".