Bonding of piles to the electrical grounding system

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klm0824

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We have pre-stressed concrete piles being installed on a project I am working on. These are loaded with rebar. Do you consider these grounding electrodes as defined in 250.52, and do they have to be bonded to the grounding electrode system? If they need to be bonded, what method do you use to get at the rebar in the pile if there are no uplift connectors?

If they are not considered "grounding electrodes" for the ELECTRICAL system, then what are they considered? They will probably act as the best grounding electrode for miles.
 
They are grounding electrodes and grounding electrodes must all be bonded together, but your situation is a little different since the only way to reach the electrode is to bust through concrete, so I wouldn't take any action on the piles. Don't bond to them; you are only required to bond to the rebar on new foundations before the concrete is poured.

Although the piles would have been great grounding electrodes, you will have to use something else. I don't know what other items the project is installing, but if nothing else, you can use ground rods.
 
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redtail_MH said:
They are grounding electrodes and grounding electrodes must all be bonded together, but your situation is a little different since the only way to reach the electrode is to bust through concrete, so I wouldn't take any action on the piles. Don't bond to them; you are only required to bond to the rebar on new foundations before the concrete is poured.

Although the piles would have been great grounding electrodes, you will have to use something else. I don't know what other items the project is installing, but if nothing else, you can use ground rods.
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I believe the latest code does not give you an option on this. If a GE is there, you have to use it.

I would argue the piles are not a GE as specified in the code.

(3) Concrete-Encased Electrode. An electrode encased
by at least 50 mm (2 in.) of concrete, located within and
near the bottom of a concrete foundation or footing
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A pile is neither a foundation nor a footing.
 
The piles will be an integral part of the foundation once the pile cap is poured. So, tecnically, they are the foundation.

I agree that if a GE electrode is present, it has to be bonded. I also think that it doesn't matter if it is a "made electrode" that is intended to be part of the electrical ground system or not. If it is there, bond it.

What I have been struggling with pertains mostly to when lightning strikes. I think that bonding these piles makes a safer installation because they help make the voltage gradient smaller.
 
You can also argue if the piles go in before the slab and footing they are existing and not required to be used as a CEE.
 
klm0824 said:
What I have been struggling with pertains mostly to when lightning strikes. I think that bonding these piles makes a safer installation because they help make the voltage gradient smaller.
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Why do you think that?

Even if you had zero Ohms to ground it does not increase what minimal level of protection from lightning a GE gives you.
 
klm0824 said:
The piles will be an integral part of the foundation once the pile cap is poured. So, tecnically, they are the foundation.
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I still think the foundation sits on top of the piles, and the piles are not the foundation. One could argue they are the footing though.

Sounds like something the architect/engineer/AHJ ought to decide before much more work is done.
 
petersonra said:
Why do you think that?

Even if you had zero Ohms to ground it does not increase what minimal level of protection from lightning a GE gives you.
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These piles are 80 feet long, installed in good soil. LOTS of piles. If steel is bonded to piles (and the electrical ground grid), there are lots of paths to earth if lightning strikes.
 
klm0824 said:
These piles are 80 feet long, installed in good soil. LOTS of piles. If steel is bonded to piles (and the electrical ground grid), there are lots of paths to earth if lightning strikes.
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Not unless you have more than one GEC.

Think what the impedance of a #6 or #4 conductor is at the high frequencies a lightning bolt exhibits.
 
It doesn't matter what they are...if I am the structural engineer, you will replace the pile if you cut into it to connect a grounding electrode conductor.
Don
 
Okay, let me complicate the issue. What if the piles are bare steel pipe with a 20 ft section of casing at the top section ( for environmental reasons)?

Same scenario, pile cap is poured around the pile at the top. Lots of long piles. The rebar in the foundations (pile caps) is bonded to the grid with #2/0 AWG.

Do you need to bond the pipe pile and the casing to the foundation rebar or the grid? Even if NEC doesn't require that they be bonded, isn't it prudent to bond them to the rebar as a minimum?
 
I agree with Don's statement completely.

Now if you don't have to bust out concrete, go ahead and bond the piles to the gronding electrode system.
 
If you install a CEE in the footing why would the piles need to be bonded at all? Does the NEC require that all concrete encased rebar be bonded together? I say no. If the CEE is available in the footing and that is used no further bonding of the piles is required.
 
I think an important point in the original post is that the piles are prestressed. I doubt anyone would want to weld onto the steel, which is often pulled banjo string tight.

Code doesn't require every piece of foundation steel to be used as an electrode, just that one be used.

Jim T
 
jtester said:
ICode doesn't require every piece of foundation steel to be used as an electrode, just that one be used.
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Actually, 250.50 requires "All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system". Stricktly by the words of the code, any section of foundation steel at least 20' long would need to be included in the grounding electrode system. There is a proposal for the 208 NEC that, if adopted, will only require one concrete encased electrode to be used.
 
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