Hi, I would like to use the rebar encased in the slab that is going to have a manufactured home installed on it as the GES. The slab is 8" thick and the rebar is 1/2" and is over 20'long. It is going to have contact with the earth on the sides. Can this be used per NEC? Thanks any input please.
grounding electrode system (ufer)
- Thread starter elecmen
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- Placerville, CA, USA
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- Retired PV System Designer
The code language is pretty clear that a permitted/required CEE must include a footing and not just a slab. You are correct that an insulating layer (plastic, tar, or foam, etc.) under a concrete mass disqualifies it as a CEE while insulation on one or both vertical sides does not.
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kwired
Electron manager
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- NE Nebraska
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What you describe doesn't sound like a footing. Nothing would prohibit bonding rebar in the slab, but it also isn't a qualifying electrode and you must use some other qualifying electrode.
wwhitney
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Does it have a thickened edge? If so, that portion plays the role of the footing.
Cheers, Wayne
Dale001289
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- Georgia
petersonra
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- Northern illinois
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- engineer
read carefully this part of what you cited.
the slab itself is neither a foundation or a footing.
Dale001289
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- Georgia
Semantics perhaps? I believe it meets the intent of the Code.
petersonra
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not semantics. it is what the code actually says. they carefully left out allowing the slab to be used as a ufer. I have no idea why, but they were very careful to make it clear a slab did not count.
Dale001289
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- Georgia
The code doesn't cover every conceivable scenario - at some point one must evaluate the intent.
petersonra
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- Northern illinois
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- engineer
in this case it specifically excludes what you are advocating doing.
the first part of the paragraph refers to foundation or footing.
the second part to something being vertical.
the slab is not vertical, not a foundation, and not a footing. therefore it just plain cannot qualify as a CEE.
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- Retired PV System Designer
One potential significant difference is that the slab is in contact with suface soil only, which may be dry and have significantly higher resistivity than the deeper soil around a footing/foundation.
The concept of the UFER ground is that it can be usable even in dry and rocky soil, but the Code tries to provide for the best possible result in every situation.
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I agree with Bob. The code says "footing" for a reason. And while it is true that the code writers can't see every possible situation a concrete slab is not some mysterious thing only found in small parts of the world.
Dzboyce
Senior Member
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- Royal City, WA
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- Washington 03 Electrician & plumber
I deal with this in building pump houses.
slab on grade; no ufer, 2 grounding electrodes.
if it has footings, a ufer is required in Washington. Had a customer build a brick pump house to match the main building. Put two ground rods in. Electrical inspector said nope. Have to connect to rebar in footings. Concrete contractor didn’t leave me any exposed rebar to bond to. Had to dig down 18” around entire building and install a continuous loop of bare copper, can’t remember what size. Good thing it was only a 10’x12’ Pump house.
concrete runners for a mobile or modular home are not footings.
slab on grade; no ufer, 2 grounding electrodes.
if it has footings, a ufer is required in Washington. Had a customer build a brick pump house to match the main building. Put two ground rods in. Electrical inspector said nope. Have to connect to rebar in footings. Concrete contractor didn’t leave me any exposed rebar to bond to. Had to dig down 18” around entire building and install a continuous loop of bare copper, can’t remember what size. Good thing it was only a 10’x12’ Pump house.
concrete runners for a mobile or modular home are not footings.
packersparky
Senior Member
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- Wisconsin
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- Inspector
IMO a slab can be a foundation. They are sometimes treated as such around here.
- Occupation
- Licensed Electrician
You must be referring to a mono pour, where the edge of the concrete is turned down and is burrried in the dirt at least 24".
A regular four or six inch slab is no more a foundation than a city side walk.
Agree - without the turndown, it’s a floating slab.
Dzboyce
Senior Member
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- Royal City, WA
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- Washington 03 Electrician & plumber
A concrete slab with a thickened edge is not considered a footing by my AHJ
petersonra
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- Northern illinois
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- engineer
It might depend on how thick it is. If you required to I have a 24 inch footer and it goes down 24 in it's a legitimate footer. But not all floating slabs have a footer. Some just have like a beam of concrete under the slab.
kwired
Electron manager
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- NE Nebraska
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- EC
If there is no qualifying steel in the footing, then NEC doesn't require you to put one there. Is still optional to put one there though.
Inspectors requiring you to install a ground ring instead aren't exactly right in doing so. If there is qualifying steel in the footing NEC says you must use it as a grounding electrode.
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