Steel Building/Concrete Slab

jmellc

Senior Member
I just read some of the posts about concrete encased electrodes. I have a similar question.

A customer is ordering a steel building, sort of a Quonset hut type. Will have a concrete slab. I have not been involved in wiring this type of building before. Would I need a 20 foot ground rod to bond to the rebar/grid wire? Would I be good to lay 20 feet of #4 bare cu & bond to rebar/grid wire with split bolts or would I have to cadweld? I plan to also drive 2 ground rods as usual and ground the meter base from there.

Will I need bonding jumpers at corners to bond metal base plates? Any jumpers for the metal siding and roof?
 

Smart $

Esteemed Member
I just read some of the posts about concrete encased electrodes. I have a similar question.

A customer is ordering a steel building, sort of a Quonset hut type. Will have a concrete slab. I have not been involved in wiring this type of building before. Would I need a 20 foot ground rod to bond to the rebar/grid wire? Would I be good to lay 20 feet of #4 bare cu & bond to rebar/grid wire with split bolts or would I have to cadweld? I plan to also drive 2 ground rods as usual and ground the meter base from there.

Will I need bonding jumpers at corners to bond metal base plates? Any jumpers for the metal siding and roof?
You said concrete slab but mention nothing about any foundation (aka footer). When there are footers, that's the usual place for CEE, because the concrete is typically in direct contact with undisturbed earth. In many cases a slab is not because of aggregate subgrade, vapor barrier, etc.

Next, if there is 20ft of rebar (either single piece or wire-tied sections) in the earth-contacing concrete, there is no need to add any copper other than to make the connection (not required to be larger than #4). Grid wire is non-compliant. Rebar has to be 1/2" (#4) or larger.

Listed clamps are okay, or "equally substantial approved means" [250.70].

If you have a compliant CEE, there is no need for the ground rods.

Bonding the metal siding/roof is debatable, and with any structural metal framework requiring bonding, why debate and just bond it... :)
 
Last edited:

kwired

Electron manager
I just read some of the posts about concrete encased electrodes. I have a similar question.

A customer is ordering a steel building, sort of a Quonset hut type. Will have a concrete slab. I have not been involved in wiring this type of building before. Would I need a 20 foot ground rod to bond to the rebar/grid wire? Would I be good to lay 20 feet of #4 bare cu & bond to rebar/grid wire with split bolts or would I have to cadweld? I plan to also drive 2 ground rods as usual and ground the meter base from there.

Will I need bonding jumpers at corners to bond metal base plates? Any jumpers for the metal siding and roof?
Along with what Smart$ said, cadweld is one way to connect, but not the only way. Typical split bolts however are likely not listed for this application.

If you do not have a qualifying CEE present you are not required to make one be present, but certainly can choose the option to make one. In other words, if the building design does not have the required 1/2 inch rebar in the footers and at least 20 feet of it, NEC considers a CEE to not be present and does not make us install one.
 

jmellc

Senior Member
You said concrete slab but mention nothing about any foundation (aka footer). When there are footers, that's the usual place for CEE, because the concrete is typically in direct contact with undisturbed earth. In many cases a slab is not because of aggregate subgrade, vapor barrier, etc.

Next, if there is 20ft of rebar (either single piece or wire-tied sections) in the earth-contacing concrete, there is no need to add any copper other than to make the connection (not required to be larger than #4). Grid wire is non-compliant. Rebar has to be 1/2" (#4) or larger.

Listed clamps are okay, or "equally substantial approved means" [250.70].

If you have a compliant CEE, there is no need for the ground rods.

Bonding the metal siding/roof is debatable, and with any structural metal framework requiring bonding, why debate and just bond it... :)
Thanks, the rebar info makes sense. About the siding and roof, I am asking because I have not been involved in this kind of building before and am trying to go with both code and standard procedure, if there is a standard procedure. I want to do whatever makes a good job with the safest most effective grounding/bonding methods.
 

Smart $

Esteemed Member
... About the siding and roof, I am asking because I have not been involved in this kind of building before and am trying to go with both code and standard procedure, if there is a standard procedure. I want to do whatever makes a good job with the safest most effective grounding/bonding methods.
I've not been involved with this type either. Shouldn't take much to bond the shell. If it has any type of metal framework, that's required to be bonded anyway. Just a question of whether or not the shell metal is bonded by attachment to the framework. I can only guess that it is.
 

ceb58

Senior Member
I just read some of the posts about concrete encased electrodes. I have a similar question.

A customer is ordering a steel building, sort of a Quonset hut type. Will have a concrete slab. I have not been involved in wiring this type of building before. Would I need a 20 foot ground rod to bond to the rebar/grid wire? Would I be good to lay 20 feet of #4 bare cu & bond to rebar/grid wire with split bolts or would I have to cadweld? I plan to also drive 2 ground rods as usual and ground the meter base from there.

Will I need bonding jumpers at corners to bond metal base plates? Any jumpers for the metal siding and roof?
If it is the Quonset hut type the panels will come in about 2 1/2 ft wide sections. The one we put up for my son was 30' long and 15' to the peak. there were 5 panels per section that all bolt together. You get all 5 panels loosely bolted and stand it up matching it to a section you have up. ( I have helped do 2 of these type buildings. The first and the last.) But as far as wiring what I did was remove bolts from the side and attach uni-strut to the inside wall with longer bolts the same diameter reusing the rubber washer on the out side. You could do the same on the out side for the meter and inside for the panel. As far as grounding I would just drive the ground rods and not worry with the footer. You can drill and bolt a lug on one of the panels and bond it back to the panel.
 
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