250.52(A)(3) Concrete-Encased Electrode

[rlheflin]

Per NEC 250.52(A)(3)(1): ?Aconcrete-encased electrode shall consist of at least 20ft of one or more bareor zinc galvanized or other electrically conductive coated steel reinforcingbars or rods of nit less than ?? in diameter, installed in one continuous 20ftlength, or if in multiple pieces connected together by the usual steel tiewires, exothermic welding, or other effective means to create a 20ft or greaterlength?My question? Does the electrodehave to be 20ft long, or do we just need 20ft of rod in the foundation? As stated above, code says ?one continuous20ft length?, but I have others saying the ?multiple pieces? part allows you tojust put any length of rod in the foundation, as long as they are tied togetherand equal a total of 20ft (not continuous). Example: a contractor claims a 5ft deep shaftw/ (4) #4 vertical bars & #4 ties meets code. That equals 20ft total, but not continuous. I say it has to be one continuous length of20 ft. What do y?all think?

 

[iwire]

As odd as it sounds it does not have to be continuous.

 

[infinity]

Once they're tied together the NEC considers them to be continuous. All you need is 20' of #4 or larger as one piece or in any combination of lengths tied together to achieve the 20'.

Welcome to the Forum.

 

[raider1]

I agree with Rob and Bob.

But talking with a member of Panel 5 about this issue it is the feeling of Panel 5 that the re-bar should be a total linear length of 20', even though the words in 250.52(A)(3) do not state this.

Chris

 

[GoldDigger]

I agree with Rob and Bob.

But talking with a member of Panel 5 about this issue it is the feeling of Panel 5 that the re-bar should be a total linear length of 20', even though the words in 250.52(A)(3) do not state this.

Chris

One strong reason that the linear 20' is important is the zone of influence problem. Common sense tells us that 10 two-foot pieces tied together in a bundle are not going to be much better than a single two-foot piece. And separating them through a one foot diameter cylinder is not going to help much either.
Going around a corner instead of in a straight line or going vertically instead of horizontally (like in a pier footing) should not be a problem.

In any case, continuing past the definition, the code approves use of a UFER (under the definition) as the sole or primary grounding electrode only when it is part of a foundation or footing. There are two parts to the functioning of a UFER: The conductivity between the rod and the mass of concrete and the conductivity between the mass of concrete and the earth.

 

[infinity]

I agree with Rob and Bob.

But talking with a member of Panel 5 about this issue it is the feeling of Panel 5 that the re-bar should be a total linear length of 20', even though the words in 250.52(A)(3) do not state this.

Chris

I see your point, two 10' sections tied with a 1' overlap would be 19' linear feet but 20' feet of rebar.

 

[ActionDave]

In any case, continuing past the definition, the code approves use of a UFER (under the definition) as the sole or primary grounding electrode only when it is part of a foundation or footing. There are two parts to the functioning of a UFER: The conductivity between the rod and the mass of concrete and the conductivity between the mass of concrete and the earth.

two 10' sections tied with a 1' overlap would be 19' linear feet but 20' feet of rebar.

I like GD's way of resolving this concern.

 

[GoldDigger]

I see your point, two 10' sections tied with a 1' overlap would be 19' linear feet but 20' feet of rebar.

I think that one is already taken care of. Tying two 10' sections together with a 1' overlap will not "... create a 20ft or greater length?

 

[infinity]

I think that one is already taken care of. Tying two 10' sections together with a 1' overlap will not "... create a 20ft or greater length”

The point that Chris was trying to make in post #4 is that the wording is rather ambiguous since it does not use the word linear to describe the overall length. I think that many would agree that the linear length should be a minimum of 20' after the smaller sections are tied together but if you think about it what's the difference between 1-20' rebar or 2-10' rebars with a 1' overlap? You still end up with 20' of rebar in the footing.

 

[iwire]

Consider 20 - 1' sections of rebar tied in a bundle, it would meet code but would not be nearly effective as 20' of rebar in a straight line.

 

[kwired]

Consider 20 - 1' sections of rebar tied in a bundle, it would meet code but would not be nearly effective as 20' of rebar in a straight line.

Or 20' of 4AWG in a tight coil vs a straight line.

 

[mwm1752]

Footers are designed to be below the frost levels of the geographic areas they are installed and IMO I would interprete the UFUR surounding mass be located below frost level. -- a 3' square concrete pad ( something a pier may be attached to) with min 30" 4# rebar tied in a grid of 4 each way below the frost level should meet the requirement of the NEC. I prefer a peice of rebar tied to the continuous rebar of the entire footing as long as there is sufficient contact with multiple steel ties.

 

[infinity]

Consider 20 - 1' sections of rebar tied in a bundle, it would meet code but would not be nearly effective as 20' of rebar in a straight line.

Agreed. IMO the code wording needs a little work.

 

[raider1]

Consider 20 - 1' sections of rebar tied in a bundle, it would meet code but would not be nearly effective as 20' of rebar in a straight line.

Agreed. IMO the code wording needs a little work.

I agree, as written in 250.52(A)(3) 20 1' sections of re-bar tied in a bundle would qualify as a CEE. CMP5 has always intended the 20' of re-bar to be a linear length but the wording needs some clarification. I see a proposal coming for the 2017 NEC.

Chris

 

[ActionDave]

Are there guys out there bundling up scraps of rebar to make their own CCE?
Sounding like a solution in search of a problem.

 

[suemarkp]

For the OP's situation,I think you need to keep reading 250.52(A)(3). It says the metallic portions shall be located horizontally in the portion of foundation/footing in direct contact with the earth. There is more about vertical foundations or structural components, but I think the "located horizontally" applies to all of those. But as iwire said, just put four 5' bars at the bottom of the foundation, tie them together, and you are good per the code. But I don't think you can count the vertical sections.

 

[GoldDigger]

The point that Chris was trying to make in post #4 is that the wording is rather ambiguous since it does not use the word linear to describe the overall length. I think that many would agree that the linear length should be a minimum of 20' after the smaller sections are tied together but if you think about it what's the difference between 1-20' rebar or 2-10' rebars with a 1' overlap? You still end up with 20' of rebar in the footing.

Simple from the theoretical side: The one foot overlap can only be counted once since the two sections are well within each other's zone of influence and therefore do not act independently to reduce the rod to concrete resistance.

 

[infinity]

Simple from the theoretical side: The one foot overlap can only be counted once since the two sections are well within each other's zone of influence and therefore do not act independently to reduce the rod to concrete resistance.

That's all well and good but that's not what the wording of the section says. Chris stated that the goal for CMP5 was to have a linear length not less than 20' but the wording doesn't really support that goal.

 

[kwired]

That's all well and good but that's not what the wording of the section says. Chris stated that the goal for CMP5 was to have a linear length not less than 20' but the wording doesn't really support that goal.

And they have had how many opportunities to change the wording? Not like this was something new in the last edition.:roll:

 

[infinity]

And they have had how many opportunities to change the wording? Not like this was something new in the last edition.:roll:

Sometimes things like this get overlooked for a long time. Don's recent change about the wording on parallel conductors took a few attempts before it was changed.

Now that it's been discussed here on the open forum I'm sure that there will be numerous proposals to add the word linear to this requirement in the 2017 cycle.