20 feet of rebar

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pms13031

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Argument at my office about the meaning of the 20 foot length of one or more 1/2" rebars being a GE. Is the meaning one length of rebar at least 20 feet long, or can I consider four 5 foot lengths as a GE? :-?
 
You can tie shorter pieces together to come up with 20'


250.52(A)(3)

consisting of at least 6.0 m (20 ft) of 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,
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Roger
 
Roger,

According to this article then, any foundation that contains 20' or more rebar (adding all together that are touching each other) MUST be tied to the system ground grid?

Also, what if you have one slab, lets say 100'x100'. And there is over 1000' of rebar. Do you only need to ground this at one point? Or is there somewhere in the NEC where it states the interval in which to ground?

Thanks,
mrrjw
 
Not sure which edition of the NEC is enforced in your area but the last sentence of 250.52(A)(3) addresses exactly what you are asking. Speaking about the 2008 NEC

Pete
 
mrrjw said:
Also, what if you have one slab, lets say 100'x100'. And there is over 1000' of rebar. Do you only need to ground this at one point?
Thanks,
mrrjw
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You only need to bond the rebar at one point -- some use a db clamp that is suitable for use in concrete, while others have the guys who build the footings turn a piece of rebar out into a crawl space.

If you stub out the rebar below grade you will have problems since the rebar in soil is corrosive and won't last long. (I think) :grin:
 
I should have posted the whole section.

(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of 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, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.
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Roger
 
The last sentence in Roger's post (#8) was added in the 2008 NEC. Prior to that some inspectors were requiring every footing that had 20' or more of 1/2" rebar to be bonded together. Glad that they cleared that one up. :roll:
 
mrrjw said:
Roger,

According to this article then, any foundation that contains 20' or more rebar (adding all together that are touching each other) MUST be tied to the system ground grid?

Also, what if you have one slab, lets say 100'x100'. And there is over 1000' of rebar. Do you only need to ground this at one point? Or is there somewhere in the NEC where it states the interval in which to ground?

Thanks,
mrrjw
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I do not believe that the rebar in a "slab" has to be bonded at all, with exception of animal confinement. Only the rebar in a footing.
 
ptonsparky said:
I do not believe that the rebar in a "slab" has to be bonded at all, with exception of animal confinement. Only the rebar in a footing.
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I was thinking the same thing as I read the original post.
The steel under a slab of concrete doesn't qualify as a Grounding Electrode.

Although, it wouldn't hurt anything to bond it, and I probably would.
As you noted, it's required under some circumstances.

steve
 
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