Re-bar ground required in Precast?

[In-spector]

I've been working as a third party inspector inspecting installations of compressor stations and metering sites in the natural gas industry. We make our contractors adhere to NEC250.52(A)(3) for all pipe supports, equipments pads, foundations, etc..where 20 ft or more of re-bar is used. Lately the contractor has been bringing in pre-cast concrete supports. We can find no way to adhere to 250.52 without chopping into the precast. We were told the lifting eyes were tied into the re-bar but checked between eyes with a continuity tester and got no continuity. Is pre-cast exempt from 250.52?

 

[augie47]

(Based on your 1st sentence and the type of question I approved your post, but please complete the pertinent data in your profile. Thanks)

 

[infinity]

I've been working as a third party inspector inspecting installations of compressor stations and metering sites in the natural gas industry. We make our contractors adhere to NEC250.52(A)(3) for all pipe supports, equipments pads, foundations, etc..where 20 ft or more of re-bar is used. Lately the contractor has been bringing in pre-cast concrete supports. We can find no way to adhere to 250.52 without chopping into the precast. We were told the lifting eyes were tied into the re-bar but checked between eyes with a continuity tester and got no continuity. Is pre-cast exempt from 250.52?

Where in that section does it say that these items must be part of the CEE?

Welcome to the Forum.

 

[In-spector]

Electrical Inspector

Electrical Inspector

250.50 states "All grounding electrodes as described in 250.52(A) (1) through (A) (7) that are present at each bldg or structure served shall be bonded together to form the grounding electrode system." So my question is how does a precast structure become part of the GES?

 

[GoldDigger]

250.50 states "All grounding electrodes as described in 250.52(A) (1) through (A) (7) that are present at each bldg or structure served shall be bonded together to form the grounding electrode system." So my question is how does a precast structure become part of the GES?

If there is not a connection brought outside the concrete, there is no CEE regardless of how much concrete and rebar there is. Therefore you do not have to connect to it.

 

[jxofaltrds]

250.50 states "All grounding electrodes as described in 250.52(A) (1) through (A) (7) that are present at each bldg or structure served shall be bonded together to form the grounding electrode system." So my question is how does a precast structure become part of the GES?

How do you know that you have an electrode per 250.52(A) (3)?

If there is not a connection brought outside the concrete, there is no CEE regardless of how much concrete and rebar there is. Therefore you do not have to connect to it.

Lack of a connection point outside of the concrete does not make the CEE disappear.

Everything you didn't want to know about rebar:

http://www.crsi.org/Resources/technical/PDF/CRSI-Specialty_Steel_Product_Guide.pdf

 

[GoldDigger]

How do you know that you have an electrode per 250.52(A) (3)?
Lack of a connection point outside of the concrete does not make the CEE disappear.

So if a contractor poured a pad for a detached garage, with no CEE connection point and the EC then put in two ground rods per NEC, you would fail the installation because the CEE was not connected? I have to disagree with you on that one.

However, some local building codes require more than the NEC for GES, including requiring either a CEE or a ground ring regardless of other electrodes available. In a case like that, the absence of a CEE termination point is not an excuse and the EC will have to either break the concrete to make the connection or install a ground ring. He gets to choose the least expensive and disruptive.

 

[jxofaltrds]

So if a contractor poured a pad for a detached garage, with no CEE connection point and the EC then put in two ground rods per NEC, you would fail the installation because the CEE was not connected? I have to disagree with you on that one.

However, some local building codes require more than the NEC for GES, including requiring either a CEE or a ground ring regardless of other electrodes available. In a case like that, the absence of a CEE termination point is not an excuse and the EC will have to either break the concrete to make the connection or install a ground ring. He gets to choose the least expensive and disruptive.

Then why the exception?

250.50
Exception: Concrete-encased electrodes of existing buildings
or structures shall not be required to be part of the
grounding electrode system where the steel reinforcing bars
or rods are not accessible for use without disturbing the
concrete.

 

[GoldDigger]

Then why the exception?

250.50
Exception: Concrete-encased electrodes of existing buildings
or structures shall not be required to be part of the
grounding electrode system where the steel reinforcing bars
or rods are not accessible for use without disturbing the
concrete.

Touche!

I still have problems when there are multiple CEEs, as in the situation the OP describes where precast concrete components are used. If there are 15 separate CEEs for one structure, do you have to bond all of them or only one of them. (I lean toward it being the latter based on rules as applied to other types of electrodes, but I still don't like the result. )
By extension, a rod electrode which is inadvertently driven too deep or covered over by a pour of concrete would have to be excavated so that a connection could be made to it, rather than just driving a replacement.

 

[jxofaltrds]

"......If multiple concrete-encased electrodes are present at a building or
structure, it shall be permissible to bond only one into
the grounding electrode system."

 

[GoldDigger]

"......If multiple concrete-encased electrodes are present at a building or
structure, it shall be permissible to bond only one into
the grounding electrode system."

Which may be the solution to the OP's original problem. He just has to ensure that there is at least one usable CEE at each site and not worry about all the rest.
Now if the rebar's are not deliberately bonded, or if they are mechanically attached in a way that insulates them, then as long as there were no lengths greater than 20' there would not be a CEE?
Some have argued that the 20' requirement applies to the total linear amount of rebar in the concrete rather than one electrically continuous piece or one which is laid out to include 20' of rebar even if it is all inside a one-square foot area.
A topic that lends itself to all sorts of arguments!

 

[jxofaltrds]

Which may be the solution to the OP's original problem. He just has to ensure that there is at least one usable CEE at each site and not worry about all the rest.
Now if the rebar's are not deliberately bonded, or if they are mechanically attached in a way that insulates them, then as long as there were no lengths greater than 20' there would not be a CEE?
Some have argued that the 20' requirement applies to the total linear amount of rebar in the concrete rather than one electrically continuous piece or one which is laid out to include 20' of rebar even if it is all inside a one-square foot area.
A topic that lends itself to all sorts of arguments!

The non enforceable handbook shows 20' in a straight line. 2008 handbook I think.

No different than an 8' rod. Not (4) 2' pieces spaced 6' apart.

 

[GoldDigger]

No different than an 8' rod. Not (4) 2' pieces spaced 6' apart.

Darn, I am going to have to go back and re-do all of those!
Anyway, that means that a 19' long precast concrete piece would not be a CEE either. More help for the OP.

 

[jxofaltrds]

IMHO the approved plans should have addressed this issue.

 

[RichB]

Here's how I would handle it:

1. Use 250.50.
2. This is "pre-cast" and any digging/chipping/drilling into it wouold void any warranty
3. Looking at #'s 1 and 2--Leave it as is and don't call it a CEE and don't worry about it.
4. Ensure all other methods are used and that the intent of the NEC is met.

Just my opinion and how I would look at it as an inspector.

 

[In-spector]

CEE

CEE

Called the pre-cast manufacturer today who said they can build the pre-cast to include a CEE with a ground point of attachment (usually the lift eye or hold down bolt painted green) if they know it ahead of time. Otherwise there is no accommodation for the CEE.

 

[iwire]

I wonder how that would work in my area. Here the inspector must inspect the CEE before the cement gets poured.

 

[iwire]

So if a contractor poured a pad for a detached garage, with no CEE connection point and the EC then put in two ground rods per NEC, you would fail the installation because the CEE was not connected? I have to disagree with you on that one.

Check this out from where I am.

I have not heard of it happening but they do want the CCE used.

 

[GoldDigger]

Check this out from where I am.

I have not heard of it happening but they do want the CCE used.

Beautiful! Was the NEC provision statung that only one CEE needs to be connected added in a later cycle, or did Mass just override ir?
Among other things, this implies that if there are two 20' lengths of rebar in one pour that are not properly bonded both must be separately connected externally instead.
Fortunately precast concrete is more often used above ground than as a foundation.

 

[suemarkp]

250.50 states "All grounding electrodes as described in 250.52(A) (1) through (A) (7) that are present at each bldg or structure served shall be bonded together to form the grounding electrode system." So my question is how does a precast structure become part of the GES?

My fundamental question in this thread is what is the requirement for each of these structures to have a ground electrode system? Is there a feeder going to them or a Service? If there are branch circuits passing through or powering things on those precast slabs, a ground electrode system is not required. I'd argue that 250.50 does not have to be done if no ground electrode system is required. Kind of like building a sprinkler distribution box in your yard with metal pipes. Just because you have a bunch of pipe in the ground that is metal doesn't mean you have ground electrodes and they must be bonded together. If there is no power at that distribution box, or otherwise no reason for an electrical inspector to look at it, then you should not need to bond anything.