Concrete encased electrodes

[britt]

If the service on a single family dwelling hits the garage first I ground to the rebar in the slab of the garage per 250.50. My question is what about the rebar in the slab for the house? Does this have to be grounded to the rebar in the garage slab? What if the service hits the house first? Do I have to ground to the rebar in the garage slab? Any comments would be greatly appreciated

 

[jwelectric]

Re: Concrete encased electrodes

In your question you have made reference to the rebar that is part of a slab. To the best of my knowledge you are not required to bond any rebar that is part of a slab that is any part of a house unless this slab is part of the walking surfaces that surround a pool.

If you are referring to using this rebar as part of the grounding electrode system then it must comply with part III of 250.

250.50 Grounding Electrode System.
All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system.

This states that ALL grounding electrodes shall be bonded together to form the grounding electrode system. The rebar that is part of a slab for the purpose of reinforcing the concrete slab is not part of the grounding electrode system as outlined in 250.52 (A) (3)

250.52 (A) (3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within AND near the bottom of a concrete foundation or footing that is in direct contact with the earth,

In order for rebar to be part of the grounding electrode in must be in the foundation or footing. If this pad is a turn down pad then that part of the rebar that is located in the turn down portion of the pad would then be part of the grounding electrode system.

 

[britt]

Re: Concrete encased electrodes

Thanks for the quick reply jw. Sorry, I meant the rebar in the footers and not for reinforcing the slab. So I gather from your response that you believe that the rebar in the footers for the house slab and the garage slab must be bonded together?

 

[jwelectric]

Re: Concrete encased electrodes

britt

I will not tell you not to bond all the rebar together, the more the better for the dissipation of unwanted current.
The code only requires that 20 ft. be used.

250.52 (3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.

Hope that this helps.