Rebar to ground GRID requirements

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Dennis Alwon

Dennis Alwon

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I got this question from a new member in a pm

Jeffro Wagner said:
We are a large industrial generating site performing site upgrades. We have a large 800'+ by 1600'+ site ground GRID/MAT. A contractor we have hired is installing a very thick (3'+) rebar reenforced concrete roadway (for a 200T transporter) through the ground grid and they are saying that there is no code requirement to attach the rebar to the gound grid/mat. With the entirety of the ground gird/mat surrounding the roadway, we argue that cadwelding of the rebar to the plant ground grid/mat is required, but they won't budge.

Thoughts,
Jeffro
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As I said in my pm I posted this here but I want clarification whether this rebar is part of the building footings. It does not sounds like it so I don't see the requirement however it would not hurt to do so.
 
Rebar to ground GRID requirements

The contrete pad is NOT part of a building foundation (roadway or haul path for heavy load), but is entirely within the boundary of an existing plant ground grid. I see this as a Ground Potential Rise issue for anyone crossing this roadway and a fault occurs (lightning induced or 7.2KV cable failure as there are lots of them underground in the area).
 
Again I see no code requirement for it however some of the other more qualified individuals we have here may address the issue you worry about
 
Jeffro Wagner said:
The contrete pad is NOT part of a building foundation (roadway or haul path for heavy load), but is entirely within the boundary of an existing plant ground grid. I see this as a Ground Potential Rise issue for anyone crossing this roadway and a fault occurs (lightning induced or 7.2KV cable failure as there are lots of them underground in the area).
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I am not really sure why you are asking. the grid is not required by the NEC. From your description, I suppose it may be covered in your local utility codes. If you want it bonded, issue a change request and get it bonded. Otherwise don't bond it. Generally speaking you can't do too much bonding, so the real driving force is what you are willing to pay for.
 
Jeffro Wagner said:
The contrete pad is NOT part of a building foundation (roadway or haul path for heavy load), but is entirely within the boundary of an existing plant ground grid. I see this as a Ground Potential Rise issue for anyone crossing this roadway and a fault occurs (lightning induced or 7.2KV cable failure as there are lots of them underground in the area).
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Grounding grids are not NEC mandated... so I agree with Dennis that it is not a Code issue. You will likely have to resort to other avenues.

Is the existing ground grid/mat being interrupted from a discontinuity perspective? If so, get the project engineers involved. May be an oversight on their part.

Is there anything in their contract that would compel the contractor to bond the grid to the rebar?
 
Is this ground mat part of an substation grounding mat? Extensive grounding mats are used in high voltage substations and similar installations to limit the step and touch potential if there is a fault.
 
don_resqcapt19 said:
Is this ground mat part of an substation grounding mat? Extensive grounding mats are used in high voltage substations and similar installations to limit the step and touch potential if there is a fault.
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But is it required by NEC? It seems that the Op was concerned about the fault current
 
Jeffro Wagner said:
The contrete pad is NOT part of a building foundation (roadway or haul path for heavy load), but is entirely within the boundary of an existing plant ground grid. I see this as a Ground Potential Rise issue for anyone crossing this roadway and a fault occurs (lightning induced or 7.2KV cable failure as there are lots of them underground in the area).
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Look for this author Robert J Alonzo PE he has a couple of books on this subject and it apearse in chapter 12 page 466 your subject matter is listed
 
What are the requirements that it would not meet,lets assume all rebar was thermo welded together(or would a tie wire work) and we had some bonding leads in place lets say every 100 feet or so,,,,,,,,,,,,,,what else do we need other than tying into the grid?

dick
 
Dick I was just commenting on the grid not being a Ufer or a CEE. 250.52(3) . I am not arguing whether it is beneficial or not but it must be encased in concrete (2") and install in the foundation or footing that is in direct contact with the earth
 
Dennis Alwon said:
Dick I was just commenting on the grid not being a Ufer or a CEE. 250.52(3) . I am not arguing whether it is beneficial or not but it must be encased in concrete (2") and install in the foundation or footing that is in direct contact with the earth
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I believe Dick was referring to the roadway being the UFER/CEE
 
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If the roadway work cut the existing grid conductors and is not bonded to the grid it could create localized Step and Touch Potential hazards during a fault. The road contractor should either reconnect the cut ground wires or cadweld to the rebar, effectively using the rebar grid as a replacement for the removed ground conductors.
Or his engineer could do a ground grid analysis to prove that the area is safe during a fault.

If the road is poured on top of the existing ground conductors and they are intact, there should not be a problem.
 
Dennis Alwon said:
I understand - I was saying the grid under the roadway-- and I am saying that technically that would not qualify as a ufer. Do you think it would?
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I'm of the impression the grid was cut rather than embedded in or under the roadway. And I would only consider the roadway a ufer if bonded.
 
Dennis Alwon said:
I understand - I was saying the grid under the roadway-- and I am saying that technically that would not qualify as a ufer. Do you think it would?
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Why would it not,provided it is in a minimum of 2 inches of concrete. The only technical part of the description that does not match is the foundation, but it would serve the same physical purpose.
 
I did not pick up from the OP that the grid was cut. I understood that this is a new project and they want to utilize the grid in the roadway and tie it to the grounding system. This is not a requirement as the rebar in the roadway is not a ufer. That was my interpretation of what is going on.
 
Dennis Alwon said:
I got this question from a new member in a pm
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Sounds like a CEE.

(3) Concrete-Encased Electrode. A concrete-encased
electrode shall consist of at least 6.0 m (20 ft) of either
(1) or (2):
(1) 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, installed in
one continuous 6.0 m (20 ft) length, or if in multiple
pieces connected together by the usual steel tie wires,
exothermic welding, welding, or other effective means
to create a 6.0 m (20 ft) or greater length; or
(2) Bare copper conductor not smaller than 4 AWG
Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation or footing
that is in direct contact with the earth or within
vertical foundations or structural components or members
that are in direct contact with the earth. 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.

If not does 250.50 apply? It is present "at" yes/no?

250.50 Grounding Electrode System. All grounding electrodes
as described in 250.52(A)(1) through (A)(7) that are
present at each building or structure served shall be bonded
together to form the grounding electrode system. Where
none of these grounding electrodes exist, one or more of
the grounding electrodes specified in 250.52(A)(4) through
(A)(8) shall be installed and used.
 
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