Generator on concrete slab, is cee needed?

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mark32

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Location
Currently in NJ
Inspector wants a standby generator to be set on a concrete pad as opposed to crushed stone we normally use. The gc poured the pad, said he stubbed a piece of rebar out the side so we can clamp to it. Is this connection needed for this install? There's much less than 20' of rebar present in the slab according to him.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Inspector wants a standby generator to be set on a concrete pad as opposed to crushed stone we normally use. The gc poured the pad, said he stubbed a piece of rebar out the side so we can clamp to it. Is this connection needed for this install? There's much less than 20' of rebar present in the slab according to him.
Don't you need to connect to a ground rod? Why not use the CEE.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
With less than 20', it's not a compliant CEE (250.52(3)). OTOH, unless it's a small pad, would expect more than 20' anyway.

I assumed there were a few runs tied together but it brings up another issue-- If it is a slab with no footings then it isn't a CEE either.
 

mark32

Senior Member
Location
Currently in NJ
Thanks for the quick responses. I'm probably looking too far into this, inspector just told the gc to bang some rebar into the ground along with some mesh and pour, didn't mention a thing about bonding to it. It's a small pad, just large enough for a 17kw generator, probably not that thick either, although he did say he used 10 80lb bags of cement.
 
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Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Do you even need a grounding electrode for the generator?


Ground Rod at Outside Generator
Mike, it was interesting reading about touch potential in response to the ground rod at the light pole. According to the USDA Rural Utilities Services (RUS) Bulletin 1751F-810, a standby generator shall be grounded to a driven ground rod regardless if the generator is separately derived or derived. The RUS Bulletin wants a ground rod in place to protect personnel against step potential voltages. Therefore, when doing a Grounding Audit using the RUS Grounding Checklist, we have to verify if the frame of the standby generator is grounded to a driven ground rod.
So, based on your explanation of the ground rod at a light pole, would the same explanation hold true for a ground rod at a standby generator?
Mike Holt’s Response: A ground rod at a generator that is not a separately derived system is not required to be grounded to the earth (but it can be 250.54). If a ground rod is installed it serves no purpose in reducing step or touch voltage to a safe value. Just like the light pole ground.
Looks like ground rods are showing up all over the place. About a year ago, I saw a job where ground rods were installed inside a building to some of the steel columns. I really hate to open up a can of worms, but here I go….. “Driving ground rods “inside a building” and connecting them to the building steel columns that are not the perimeter columns is useless and serves no purpose.” Now if I am wrong, please respond with a page number, section number of some national or international standard to support your position.
Mike Holt’s Comment: If you have any comments or feedback, please let me know, Mike@MikeHolt.com
Copyright ? 2003 Mike Holt Enterprises,Inc.
1-888-NEC-CODE (1-888-632-2633)
 
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svh19044

Senior Member
Location
Philly Suburbs
In a small slab, I would almost fail to see the point of bonding to the rebar if that's what the inspector wanted to see. But if it's what he wants, it's what he gets.

There are only two questions to be asked, the most important...

What does the manufacturer suggest/require for installation?

Is it a separately derived system?

For nonseparately Derived systems, the Siemens/Generac standby's that I have installed DO call for a separate ground rod, while I don't recall the Kohler calling for one.
 
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mark32

Senior Member
Location
Currently in NJ
Hey guys, for those interested the manufacturer (Generac) wants a ground rod. As far as it being a SDS I'm unsure, I didn't open up the transfer switch but I doubt it is. As I see and figured a cee isn't likely needed/effective here, just wanted other's opinions. Thanks again.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
A slab is not a footing or foundation and would not be a CEE no matter how much rebar is in the slab.

Sorry...posting before reading again.
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
The last small Generac I installed was not an SDS, the neutral is "floating", but Generac still required a ground rod, it just attaches to a lug on the outside of the frame, but is not internally connected to the neutral.
 
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