Question 1

What are the National Electrical Code (NEC) requirements for using rebar as a grounding electrode?

Accepted Answer

The NEC, specifically Article 250.50, mandates that all available grounding electrodes, including concrete-encased electrodes (CEEs), form the grounding electrode system.  For a CEE to be recognized, it must consist of at least 20 feet of one or more electrically conductive steel reinforcing bars, ½ inch or greater in diameter, encased by at least 2 inches of concrete in direct contact with the earth.  These bars must be mechanically connected by steel tie wires or other approved means.

Question 2

Is it necessary to bond all rebar within a concrete slab to the grounding electrode system?

Accepted Answer

No, it is not necessary to bond all rebar within a concrete slab.  The NEC distinguishes between a concrete-encased electrode (CEE) and general rebar grids.  Only rebar specifically designated and constructed as a CEE, or rebar that is likely to become energized, is required to be bonded to the grounding electrode system.

Question 3

What corrosion protection measures are required for rebar used as a grounding electrode?

Accepted Answer

When a rebar-type concrete-encased electrode emerges from the concrete and is in contact with the earth, it must be provided with corrosion protection.  This requirement, found in NEC 250.68(C), ensures the long-term integrity and effectiveness of the grounding electrode.  The connection of the grounding electrode conductor to the rebar stub must also be securely made and protected.

Rebar Grounding & Bonding: NEC Requirements Explained