Rebar bonding

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Carultch

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I have pour-in-place above grade concrete footings, directly on the ground. This is for the mounting of a solar array. There is no intention for them to serve an electrical purpose, and no electrical conduit or wiring is installed in any of them.

Each footing has two layers of field-tied rebar grids, that are discontinuous from one another.

#1: is electrical grounding of the rebar required?
#2: is it required to connect wire to all discontinuous pieces/assemblies of rebar? Or simply one piece of rebar within each footing, assuming that concrete establishes the electrical continuity after it is poured?
 
Are you trying to use the rebar as a grounding electrode? If so you only need to use one if the rebar is 1/2" or larger and 20' or longer.
 
infinity said:
Are you trying to use the rebar as a grounding electrode? If so you only need to use one if the rebar is 1/2" or larger and 20' or longer.
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Not trying to use it as a grounding electrode, just trying to use it as weight. No piece of rebar exceeds 10 ft. Rebar is larger than 1/2" nominal.
 
Since it's less than 20' it doesn't qualify as an electrode and you're not trying to use it as an electrode so IMO you do not need to do anything.
 
infinity said:
Since it's less than 20' it doesn't qualify as an electrode and you're not trying to use it as an electrode so IMO you do not need to do anything.
Click to expand...

Here's my example..

We are about to install new transformer foundations in an industrial facility. Typical installation calls for a buried ground loop and ground rods around the transformer foundation for transformer equipment ground connections to earth. The transformer footer consists of more than 20' of 1/2" reinforced bar and meets the criteria for a Concrete-Encased Electrode in Section 250.52(A)(3) [although no EGC are tied to the rebar].

Since the ground loop is my grounding electrode, and not the rebar - Am I not required to bond the rebar to the ground loop to create a grounding electrode system as described in 250.50, even though it meets the criteria for a Concrete-Encased-Electrode? The code seems to say if I have a if my rebar is installed per 250.52(A)(3) then it needs to be bonded to the other grounding electrodes.
 
ASimEE said:
Here's my example..

We are about to install new transformer foundations in an industrial facility. Typical installation calls for a buried ground loop and ground rods around the transformer foundation for transformer equipment ground connections to earth. The transformer footer consists of more than 20' of 1/2" reinforced bar and meets the criteria for a Concrete-Encased Electrode in Section 250.52(A)(3) [although no EGC are tied to the rebar].

Since the ground loop is my grounding electrode, and not the rebar - Am I not required to bond the rebar to the ground loop to create a grounding electrode system as described in 250.50, even though it meets the criteria for a Concrete-Encased-Electrode? The code seems to say if I have a if my rebar is installed per 250.52(A)(3) then it needs to be bonded to the other grounding electrodes.
Click to expand...

IMO, you must use all available electrodes so yes the rebar must be connected to the ges(grounding electrode system)
 
Dennis Alwon said:
IMO, you must use all available electrodes so yes the rebar must be connected to the ges(grounding electrode system)
Click to expand...

That's what I figured - In reality not much additional work as long as the concrete hasn't been poured. Now off to stop the cement truck!
Thanks for the input.
 
infinity said:
Since it's less than 20' it doesn't qualify as an electrode and you're not trying to use it as an electrode so IMO you do not need to do anything.
Click to expand...

How is the 20 ft measured?

Grand total length of rebar in any given footing?
Total length of rebar segments, welded together with electrical continuity? Example, 4 qty 5 foot pieces, welded to form a mesh shaped like a "#".
Length of any individual factory rebar piece?
Length of any linear dimension of the overall concrete?
 
infinity said:
20' total, can be 4-5' pieces tied together with standard rebar tie wires.
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Yes, but I think measurement is supposed to be linear with respect to the footing. What is of importance is the earth electrode sphere of influence. Code doesn't get this specific. It is yet another of implied intentions.

Say you have a 10'+ long 12" wide footer with two parallel rebar with at least one cross tie. Is that 20' of rebar? Compare to the reasoning behind grounds rods must be at least 6' apart.

If you have a square column pad with more than 20' of rebar total and compare the sphere of influence volume to that of a straight (long, narrow) footing with one uncut 20' rebar, there will be a very contrasting volume.
 
Given the current wording it's 20' of rebar and that's it, two 10' pieces in an X shape with one tie in the middle would be complaint. There is a proposal for the 2017 to include the word linear in the discussion (for example two 11' pieces of rebar with a 1' overlap resulting in 20 linear feet) but that's poised to be rejected.
 
If you have a square column pad with more than 20' of rebar total and compare the sphere of influence volume to that of a straight (long, narrow) footing with one uncut 20' rebar, there will be a very contrasting volume.[/QUOTE]

Do you have figures on the effectiveness difference between the two?
Min covering is 2" would give a min dimension of 4" x 4" x 244" concrete block for a single length UFUR [(244" x 4" x 4)+(4" x 4" x x2)] = 3936 sq in of surface concrete area in contact with earth.
Min covering is 2" would give a min dimension of 44" x 44" x 4" concrete block using 6 - 40" pieces tied together [(44" x 44" x 2)]+(44" x 4" x4)] = 4576 sq in of surface concrete area in contact with earth.
 
Do you have figures on the effectiveness difference between the two?
Min covering is 2" would give a min dimension of 4" x 4" x 244" concrete block for a single length UFUR [(244" x 4" x 4)+(4" x 4" x x2)] = 3936 sq in of surface concrete area in contact with earth.
Min covering is 2" would give a min dimension of 44" x 44" x 4" concrete block using 6 - 40" pieces tied together [(44" x 44" x 2)]+(44" x 4" x4)] = 4576 sq in of surface concrete area in contact with earth.[/QUOTE]
See this page to start: http://www.esgroundingsolutions.com/grounding-electrode-sphere-of-influence/

Next step is to compare two parallel electrodes. Closer together, their sphere of influence overlaps and effectiveness decreases (you can't double the single volume where the spheres overlap). Carry this principle over to a square rebar cage of a column pad versus one 20' long rebar in a straight footer.

Keep in mind, I'm not saying Code requirement is this specific for it to be enforceable.
 
infinity said:
Given the current wording it's 20' of rebar and that's it, two 10' pieces in an X shape with one tie in the middle would be complaint. There is a proposal for the 2017 to include the word linear in the discussion (for example two 11' pieces of rebar with a 1' overlap resulting in 20 linear feet) but that's poised to be rejected.
Click to expand...
Compliant, I agree... but what is the "length" of concrete exposed to soil tha embeds that 20' of rebar?
 
mwm1752 said:
If you have a square column pad with more than 20' of rebar total and compare the sphere of influence volume to that of a straight (long, narrow) footing with one uncut 20' rebar, there will be a very contrasting volume.

Do you have figures on the effectiveness difference between the two?
Min covering is 2" would give a min dimension of 4" x 4" x 244" concrete block for a single length UFUR [(244" x 4" x 4)+(4" x 4" x x2)] = 3936 sq in of surface concrete area in contact with earth.
Min covering is 2" would give a min dimension of 44" x 44" x 4" concrete block using 6 - 40" pieces tied together [(44" x 44" x 2)]+(44" x 4" x4)] = 4576 sq in of surface concrete area in contact with earth.
Click to expand...

Interesting examples. I can see that you've tried to make as much contrast as possible, by comparing a linear curb to a flat square slab. Yet it is only about 16% difference in area. I was expecting a greater contrast to exaggerate the difference, probably as high as 50%.


Basic geometry tells us that a square should get more area for the materials that construct it.

One case where it wouldn't make sense to expect contact area to increase, is when the depth of the concrete body increases. For instance, building a deep block from the same amount of rebar, instead of a slab.

12 - 20" pieces of rebar. Total 20 ft
Layer 1: 3x3, at 10" O.C.
Layer 2: 3x3, at 10" O.C.
Layer vertical spacing: 10"
Cover: 2"

14" tall x 24" wide x 24" long

24"*24" = 576 in^2 in contact with the ground, if above grade.
24*14*4 + 24*24*2 = 2496 in^2 in contact with ground, if below grade.
 
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Smart $ said:
See this page to start: http://www.esgroundingsolutions.com/grounding-electrode-sphere-of-influence/

Next step is to compare two parallel electrodes. Closer together, their sphere of influence overlaps and effectiveness decreases (you can't double the single volume where the spheres overlap). Carry this principle over to a square rebar cage of a column pad versus one 20' long rebar in a straight footer.

Keep in mind, I'm not saying Code requirement is this specific for it to be enforceable.
Click to expand...

Thank you for the link. Quite interesting.

The follow up question is, how does one calculate the effective sphere of influence, when the spheres of influence overlap for a bonded pair of adjacent electrodes?

Simple example: two ground rods with 8 ft embedment, separated 8 ft.
 
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