Connection to Concrete Encased Electrode

[steveray]

2011 NEC suggests it....unfortunately I cannot cut and paste NFPA.....

Are some suggesting that the poly vapor barrier negates the "ground contact" of the concrete?How many ohms R through 2" of concrete vs. 2" of concrete + 6 mil poly?? c'mon

mj

 

[mjesse]

2011 NEC suggests it....unfortunately I cannot cut and paste NFPA.....

Found it - 2011 National Electric Code 250.52(3) - 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.

I don't buy into it. 2" rigid foam, sure. 6 mil poly, skeptical.

mj

 

[Dennis]

I thought I posted the Information note about the vapor barrier. I guess I didn't hit submit.

Informational Note: Concrete installed with insulation, vaporbarriers, films or similar items separating the concrete

from the earth is not considered to be in “direct contact”

with the earth.

 

[north star]

= = =

It has been discussed on the Mike Holt Forum...

but if they roll up that 20 linear feet of the copper

conductor, to let's say, ...something around the

diameter of 2-3 inches and place it in direct

contact with the earth in a 2-3 inch diameter area

within the footing, ...then by the Letter of the

NEC, that would be compliant ?

What say ye Electrical Officianados ?

20 ft. of copper conductor where ? ....Also,

20 "consecutive ft.", or 40 six inch long pieces

of copper ? :devil

= = =

 

[BSSTG]

Are some suggesting that the poly vapor barrier negates the "ground contact" of the concrete?How many ohms R through 2" of concrete vs. 2" of concrete + 6 mil poly?? c'mon

mj

I'm with you.

BSSTG

 

[raider1]

Why is this bothering me?I know Chris Kennedy is very opinionated about this but what do you see?

View attachment 1669

There are DB rated clamps that look just like this that are listed for re-bar, ground rods and water pipes. I would suggest getting the listing of the clamp.

Not all acorn clamps are listed for re-bar either.

Chris

 

[raider1]

Found it - 2011 National Electric Code 250.52(3) - 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.I don't buy into it. 2" rigid foam, sure. 6 mil poly, skeptical.

mj

Why would you be skeptical that a layer of 6 mil poly would render a footing not in direct contact with the earth?

The purpose of the 6 mil poly is to provide a moisture barrier between the concrete and the earth. It is the moisture within the concrete that helps lower the resistance of the CEE. Also poly would have electrical insulation properties.

The purpose of the grounding electrode is to limit the voltage imposed on the electrical system from lightning induced currents. If there is dielectric separating the concrete from the earth then the voltage in the concrete would have to reach a limit to where it will break down the dielectric material to make a connection to the earth.

Chris

 

[Dennis]

= = =It has been discussed on the Mike Holt Forum...

but if they roll up that 20 linear feet of the copper

conductor, to let's say, ...something around the

diameter of 2-3 inches and place it in direct

contact with the earth in a 2-3 inch diameter area

within the footing, ...then by the Letter of the

NEC, that would be compliant ?

What say ye Electrical Officianados ?

20 ft. of copper conductor where ? ....Also,

20 "consecutive ft.", or 40 six inch long pieces

of copper ? :devil

= = =

IMO, the 20' of copper must be linear not a circular install. Those Mike Holt guys are crazy. The wording says one continuous 20' or sections tied together with steel wire for the rebar. The fact that the rebar mentions length that makes me think linear-- although part 2) does not specifically say length that is what I would surmise. Who in their right mind would install a ball of copper.

 

[jar546]

So aside from the clamp issue. Does anyone else believe that the 2-3" of direct contact with the sandy soil and the 12"+ of contact of the side of the footer with the backfill constitutes direct contact? The entire footer will be below grade.

 

[jar546]

Maybe I'll sneak in at night and connect the CEE directly to the POCO pad mounted transformer.

 

[gfretwell]

This is the entire 2011 250.52(A)(3)

(3) Concrete-Encased Electrode. A concrete-encasedelectrode 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.

 

[raider1]

IMO, the 20' of copper must be linear not a circular install. Those Mike Holt guys are crazy. The wording says one continuous 20' or sections tied together with steel wire for the rebar. The fact that the rebar mentions length that makes me think linear-- although part 2) does not specifically say length that is what I would surmise. Who in their right mind would install a ball of copper.

The 20 liner foot is backed up by personal conversations with members of CMP5. It is the belief of CMP5 that the CEE should consist of 20' of liner length of re-bar or #4 AWG copper.

I know that the code does not specifically say that but that is the feeling of CMP5.

Chris

 

[raider1]

So aside from the clamp issue. Does anyone else believe that the 2-3" of direct contact with the sandy soil and the 12"+ of contact of the side of the footer with the backfill constitutes direct contact? The entire footer will be below grade.

In discussions with CMP5 one of the elements that makes a CEE such a good electrode is the weight of the building pushing down on the footing and making good contact with the earth. The side of the footing will not have the weight of the bui8lding to help make the connection.

With that said, there is nothing in 250.52(A)(3) that says the entire bottom of the footing must be in contact with the earth. I think that it is best if the entire bottom of the footing is in direct contact with the earth.

Chris

 

[steveray]

Maybe CMP6 can clear this one up.....

 

[raider1]

Maybe CMP6 can clear this one up.....

I think you mean CMP5.

Somebody must submit a code change proposal to address the issue.

A CMP will not usually just start changing code sections without a proposal.

Chris

 

[steveray]

That was kind of a joke Chris! I have no idea when they change CMP #'s.....I wait for people that are way smarter than me to make those changes or clarifications....I have enough to learn in the NEC without learning all of the science of it. For now I would have to allow the poly but I will try to make sure it doesn't happen...

 

[Uncle Bob]

Get over the clamp (they could use tie wire if they wanted to) or how the copper is attached to the rebar as long as there is 20' of horizontal copper encased in 2" of concrete. The rebar is not part of the concrete-incased electrode; it just used to maintain the 2" encasement requirement (hold up the copper conductor). If you didn't have horizontal rebar in the footing and used another method of maintaining the 2" requirement, the electrode is still good. E3608.1.2 And, the poly cannot enter (cover the sides) of the footing! Uncle Bob

 

[Dennis]

That was kind of a joke Chris! I have no idea when they change CMP #'s.....I wait for people that are way smarter than me to make those changes or clarifications....I have enough to learn in the NEC without learning all of the science of it. For now I would have to allow the poly but I will try to make sure it doesn't happen...

I always thought that making changes was for someone else but somehow I convinced myself to give it a try. I was surprised at my success rate. Many were accepted in principle and some were actually accepted. It really doesn't hurt and some of my proposals were written to see what the intent really was.

 

[Dennis]

Get over the clamp or how the copper is attached to the rebar as long as there is 20' of horizontal copper encased in 2" of concrete. The rebar is not part of the concrete-incased electrode; it just used to maintain the 2" encasement requirement (hold up the copper conductor). If you didn't have horizontal rebar in the footing and used another method of maintaining the 2" requirement, the electrode is still good. E3608.1.2

Most ec's don't put 20' of copper and attach to the rebar. Only one or the other is required, however I do both- 20' copper in the footer and then I attach it to the rebar.