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Illustrated Changes to the NEC, 2002 Edition - Part 2

Article 547

Agricultural Buildings

547.10 Equipotential Planes and Bonding of Equipotential Planes

The rules for equipotential planes were reorganized and completely rewritten to clarify where an equipotential plane is required and where it’s not required. The revised rule is as follows:

(A) Areas Requiring Equipotential Planes. Equipotential planes must be installed in all concrete floor confinement areas of livestock buildings that contain metallic equipment that is accessible to animals and likely to become energized.

Outdoor concrete confinement areas, such as feedlots, must have equipotential planes installed around metallic equipment that is accessible to animals and likely to become energized. The equipotential plane must encompass the area around the equipment where the animal stands while accessing the equipment.

Author’s Comment: An equipotential plane is an area where wire mesh or other conductive elements are embedded in or placed under concrete, bonded to all metal structures and fixed nonelectrical equipment that may become energized, and connected to the electrical grounding system [547.2].

(B) Areas Not Requiring Equipotential Planes. Equipotential planes are not required in dirt confinement areas containing metallic equipment that is accessible to animals and likely to become energized. All circuits providing electric power to equipment that is accessible to animals in dirt confinement areas must have GFCI protection.

(C) Bonding. Equipotential planes must be bonded to the building or structure electrical grounding system. The bonding conductor shall be copper, insulated, covered or bare, and not smaller than 8 AWG. The 8 AWG bonding conductor must terminate to wire mesh or conductive elements of the equipotential plane by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means.

FPN No. 1: Methods to establish equipotential planes are described in Equipotential Planes in Animal Containment Areas, American Society of Agricultural Engineers (ASAE) EP473-1997.

Author’s Comment: Stray Voltage Check Sheet and Dairyman's Stray Voltage Checklist are available from University of Wisconsin Cooperative Extension
Service, Madison, WI 608-262-3346.

FPN No. 2: Low grounding electrode system resistances may reduce potential differences in livestock facilities.
Intent: The intent of the revisions is to clarify that an equipotential plane is not required for indoor or outdoor dirt confinement areas, if GFCI protection is provided for electrical equipment accessible to animals in the confinement areas.

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