rebar bonding

[sparki]

we are doing two additions to existing school. These additions are not connected together. Should we bring #4 wire from one addition to another one to ground rebars?
Can we run wire from subpanel in addition grounding bar to rebar itself? will this be enough?
And if you are grounding rebar, where you go with grounding wire to.
Thanks

 

[raider1]

Re: rebar bonding

Why are you grounding rebar?

Chris

 

[bphgravity]

Re: rebar bonding

Each separate structure requires a grounding system as described in section 250.32(A). A concrete-encased electrode would be suitable for this task if it meets section 250.52(A)(3). Review these sections to ensure your installations are correct.

[ October 07, 2005, 03:42 PM: Message edited by: bphgravity ]

 

[infinity]

Re: rebar bonding

Sounds as if your adding to two opposite sides of a building. You would need to connect any available 20' section of rebar in either of the new footings. The two separate footings need not be bonded together.

 

[rcarroll]

Re: rebar bonding

I,m going to twist this if you don't mind. What if the footing had no rebar? I know you don't have to install 20' of bare copper. Would you then have to bond the lower rebar in the foundation wall that is poured on the footer to satisfy 250.50? Would it do any good? I ask as I have a debate in my office & your opinions are most welcome.Thanks, Ron

 

[George Stolz]

Re: rebar bonding

Originally posted by rcarroll:
Would you then have to bond the lower rebar in the foundation wall that is poured on the footer to satisfy 250.50? Would it do any good? I ask as I have a debate in my office & your opinions are most welcome.Thanks, Ron

I'd say the lower portion of the foundation wall is near the bottom of the foundation. It would qualify as a Ufer as described in 250.52(C).

Say hi to the other Ron for me, let him know I cut the outlet in and will refine my tape-measure-reading for next time.

 

[rcarroll]

Re: rebar bonding

Thanks George, that's what I'm thinking also. Now let me ask this, if the concrete is actually the electrode, as I think I've read on another thread, what difference does it make where you attach your bond wire? The footer is obvious cuz it's fully in contact with the earth, but a basement foundation wall is not. Only half of it is. Does this make sense or should I just go back to lurker land? Ron

 

[George Stolz]

Re: rebar bonding

...if the concrete is actually the electrode...

I'm back on the fence on this. I'm back to thinking the concrete is the husk of the electrode.

what difference does it make where you attach your bond wire?

No difference, per 250.52(C):

...Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.

Let's turn it around: Can you attach to the bottom of a ground rod? Yes, it's just more difficult. It's easier to attach to after it's driven.

For a ufer, it's easier to attach to the electrode above the concrete. So long as the electrode (in the sense of the "...electrode encased by at least 50 mm (2 in.) of concrete...") we attach to is bonded to the bottom of the foundation wall, via the usual steel tie wires, then we have effectively connected to the bottom of the foundation wall, or perhaps even the footer, if it's attached.

The footer is obvious cuz it's fully in contact with the earth, but a basement foundation wall is not. Only half of it is.

I'd wager there is more square footage of concrete exposed to soil in the foundation wall, than the footer. As Pierre has mentioned, the footer's appeal is that the weight of the structure is centralized there, providing better contact with the soil.

Does this make sense or should I just go back to lurker land?

Lurker land is a bummer. It's better to join in.