New Hampshire has an excellent Technical Document on the subject that offers several methods as alternatives to meet the code requirement. How do I share the graphics from a PDF document?
TECHNICAL BULLETIN
Application of 250.50, Grounding Electrode System and 250.52 (A) (3) Concrete-Encased Electrode
September 9, 2005
The 2005 National Electrical Code (NFPA 70-2005), adopted by the State of New Hampshire on July 1,
2005, clarifies that all qualifying concrete-encased electrodes are to be used as part of the grounding
electrode system for a building or other structure’s electrical system unless the building or other structure is
existing. The requirement does not mandate that a concrete encased electrode be installed, but that it is
used when one is present as part of the building or other structures engineering design or actual construction.
As described in 250.52 (A) (3) a qualifying electrode:
1. Is encased by at least 2” of concrete and located within and near the bottom of a concrete foundation
or footing that is in direct contact with the earth.
2. Consists of at least 20’of bare or zinc galvanized or other electrically conductive coated steel
reinforcing bars or rods that are not less that ½” in diameter.
a. In our interpretation, multiple rods or bars that total at least 20’ in length are included.
b. The bars or rods shall be permitted to be bonded together by the usual tie wires or other
effective means.
Additionally:
3. No encapsulating non-conductive coatings, such as epoxy, are used for corrosion protection.
4. No vapor barriers or insulating material that effectively isolate the concrete footing or foundation
from the earth have been used.
This requirement is for new construction of buildings or other structures that have been designed to the 2005
National Electrical Code or are “design/build” and permitted after July 1, 2005. The requirement does not
apply to buildings or other structures that were approved to the 2002 or previous National Electrical Codes or
to existing buildings or other structures where just the service or other supply system is being upgraded. It
would, however, apply to an existing building or other structure where the construction of an addition, etc.,
involves a qualifying electrode and the service or other supply system is being upgraded as part of the
construction.
Where the above described electrode exists, the connection of a 4 AWG or larger copper grounding electrode
conductor to the steel electrode must be made using a device that is listed by an approved testing agency with
respect to its suitability for concrete encasement, if installed within the foundation or footing, for direct
burial where applicable and for connection to a steel reinforcing rod or bar.
There are several ways of making a connection to the electrode itself and the method of choice will be a
matter of design and coordination. The following illustrations and explanations are intended to aid in
understanding some common methods of connection and are not intended to be all inclusive.
STATE OF NEW HAMPSHIRE DEPARTMENT OF SAFETY
Richard M. Flynn, Commissioner
Division of Fire Safety
Office of the State Fire Marshal
J. William Degnan, State Fire Marshal
Bureau of Electrical Safety and Licensing
Office: 2 Industrial Park Drive, Building 2, Concord, NH
Mailing Address: 33 Hazen Drive, Concord, N.H. 03305
603-271-3748, FAX 603-271-2257
Technical Bulletin, Concrete Encased Electrodes
Page 2
Figure 1: illustrates a 4 AWG or larger copper grounding electrode conductor that is insulated and has been
connected directly to the electrode within the foundation or footing. The connection fitting must be suitable
for concrete encasement and for attachment to the steel rod or bar. Sufficient conductor length must be left
to exit the wall in a convenient location for future connection by an irreversible connector, the exothermic
welding process or to be run directly to the appropriate equipment. The insulation on the conductor will
protect it from corrosion where it exits the concrete.
Figure 2: illustrates the same application as Figure 1 except a bare 4 AWG or larger copper grounding
electrode conductor has been used. In this case, a Rigid Nonmetallic Conduit (PVC) sleeve filled with
material satisfying the requirements of Section 110.11 has been installed. Filling the sleeve prevents the bare
conductor, the concrete and the air from contacting each other where the conductor exits the wall protecting
it from corrosion. Other methods of providing corrosion protection may also be used. As permitted in
Section 250.62, a grounding electrode conductor can be solid, stranded, insulated, covered or bare.
Technical Bulletin, Concrete Encased Electrodes
Page 3
Figure 3: illustrates an application where a rod or bar has been extended up through the concrete wall and
sill plate. This bar or rod will be left long enough to extend through the double plate and allow the
connection of the grounding electrode conductor. The advantages to this method are that the electrician can
make the connection to the rod or bar at any convenient time and it allows for future inspection of the
connection. Suitable corrosion protection, such as epoxy, has been provided for the rod or bar where it exits
the concrete.
Figure 4: illustrates an application where the rod or bar exits through the footing and the connection of the 4
AWG or larger grounding electrode conductor to the electrode will be below or within the concrete floor. As
in Figures 1 and 2 above, the connection fitting must be suitable for concrete encasement if it is within the
floor or for direct burial if below the floor and for connection to the steel rod or bar.
Technical Bulletin, Concrete Encased Electrodes
Page 4
Figure 5: illustrates an application where the electrode exits through the top of the footing. Similar to the
installation described in Figure 3, the advantages to this method are that the electrician can make the
connection to the rod or bar at any convenient time and it allows for future inspection of the connection.
Suitable corrosion protection, such as epoxy, has been provided for the rod or bar where it exits the concrete.
As noted above, these applications are not all inclusive and are only intended to describe some common
options. Through careful planning, coordination of trades and the influence of ingenuity other methods can
be developed and utilized.
The installation of a grounding electrode conductor, in this case to a concrete encased electrode, is part of an
electrical installation that is within the scope of RSA 319-C. Therefore, proper licensure is required for the
installation of the grounding electrode conductor including the connection to the electrode itself. Local
permitting and inspection requirements must also be considered and adhered to. In short, this may mean that
an inspection of the electrode may be required before the concrete is poured. If the process is not followed
the consequences could be severe, potentially resulting in a requirement to dismantle and rebuild a portion of
the foundation or footing.