Bonding to Rebar

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The NEC doesn't even say that you need to connect to the rebar. It does say that if your rebar qualifies as a concrete encased electrode (CEE) then you have to use a CEE. It can be the qualifying rebar or 20' of #4 bare copper in the footing.
 

Isaiah

Senior Member
Location
Baton Rouge
The NEC doesn't even say that you need to connect to the rebar. It does say that if your rebar qualifies as a concrete encased electrode (CEE) then you have to use a CEE. It can be the qualifying rebar or 20' of #4 bare copper in the footing.
NEC 250.50 requires bonding to rebar where available at Service entrance
 

tom baker

First Chief Moderator
Staff member
About 2012? , the code required use of s CEE as part of a grounding elecrode system for services and feeders. Before that code a CEE could be used but was not required. So bonding to rebar may not be required depending on installation date.
Someone may know the correct code cycle for CEE.
 

Isaiah

Senior Member
Location
Baton Rouge
Where available was changed to where present, when the CEE was required. Where available was not enforceable for requiring use of the rebar
NEC 250.50 requires all electrode types in 250.52 (A) (1) through (8) at each “building” or “structure served”, to be bonded together to form the grounding electrode system. Perhaps not enforceable but as a matter of good engineering judgement and practice, efforts should be made to connect qualifying concrete encased electrodes to any of the other types of electrodes in 250.52 especially on foundations that contain Motors, MCCs, Transformers, Switchracks etc. This is particularly true in hazardous areas where there large ground faults may occur and the concrete pad or foundation has electrical equipment on it. Also helps equalize potential and eliminate step-touch scenarios.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
NEC 250.50 requires all electrode types in 250.52 (A) (1) through (8) at each “building” or “structure served”, to be bonded together to form the grounding electrode system.
That is correct so if your building had 20' or more of 1/2" of larger rebar in the footing you are required to install a CEE but that does not mean that the CEE has to be the rebar. According to 250.52(C)(3) a CEE can be the aforementioned rebar OR 20' of #4 or larger copper conductor. If you choose to use the copper conductor you are not required to use the rebar. The last sentence of 250.52(A)(3) tells us that if more than one electrode is present you are only required to use one. So if the copper CEE conductors are what is preferred because they make someone feel all warm and fuzzy you can skip the rebar altogether.

250.52(A)(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.
 

Isaiah

Senior Member
Location
Baton Rouge
That is correct so if your building had 20' or more of 1/2" of larger rebar in the footing you are required to install a CEE but that does not mean that the CEE has to be the rebar. According to 250.52(C)(3) a CEE can be the aforementioned rebar OR 20' of #4 or larger copper conductor. If you choose to use the copper conductor you are not required to use the rebar. The last sentence of 250.52(A)(3) tells us that if more than one electrode is present you are only required to use one. So if the copper CEE conductors are what is preferred because they make someone feel all warm and fuzzy you can skip the rebar altogether.
Agreed
 

junkhound

Senior Member
Location
Renton, WA
Last house I built ;had a note on rebar drawing to spot weld rebar together.
Structural examiner redlines that, said no welding allowed, as the rebar required overlap and tie wires were sufficient for CEE and structural AHJ guys worried about incompetent welding reducing cross section of rebar.
 

kwired

Electron manager
Location
NE Nebraska
that is not what it says. bonding is only required if the rebar qualifies as a GE.
That and also only one connection to a qualifying CEE (when present) is all that is required. Meaning if you have more than one qualifying CEE on the premises NEC only requires you to use one of them. If you have rebar in one section but choose to use 20 ft of #4 copper in another section as a CEE then that is still acceptable and you don't have to bond to the rebar at all if you don't want to.
 

kwired

Electron manager
Location
NE Nebraska
Last house I built ;had a note on rebar drawing to spot weld rebar together.
Structural examiner redlines that, said no welding allowed, as the rebar required overlap and tie wires were sufficient for CEE and structural AHJ guys worried about incompetent welding reducing cross section of rebar.
spot weld shouldn't reduce cross section by any significant means, neither should exothermic welding methods.

Unless you have a situation of needing to have as low of resistance as possible for higher technical reasons, rebar generally comes in 20 foot lengths, just make sure you are tied onto a full piece and you will have a pretty decent electrode even if you question tie wires. It will be a better electrode than two ground rods in almost all instances.
 
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