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Concrete embedded elements, equipotential planes and voltage gradients


May 13, 1996


The 1996 NEC requires an equipotential plane to be created where concrete floors are installed or present in animal confinement areas that have electrical utilization equipment or other equipment/systems connected to an electrical grounding conductor by installing wire mesh or other conductive elements in the concrete and bonding these elements to all adjacent conductive equipment, structures, or surfaces and bonding this potential plane to the grounding electrode system for that building, structure, or area. The bonding conductor must be copper, not smaller than number 8, utilizing connectors of brass, copper, or copper alloy. Screws and bolts that are part of the connectors must be of the same materials. Reinforcing steel and mesh that is secured by tie wires is acceptable as a bonding connection for those elements where an effective bonding connection is achieved.

A "voltage gradient" is also required to be created at each animal entrance or exit to the building, structure, or area to allow an animal to move from the surface of one potential plane to another without experiencing voltage/current sensation levels that result in a unacceptable physiological reaction. USDA research has found that 8 foot copper-clad ground rods installed at a 45° angle outward from vertical and on 12 inch centers across an entrance or exit and bonded to the equipotential plane of the confinement area will provide an effective voltage gradient or ramp from one potential plane to another.

Animal confinement areas requiring equipotential planes and voltage gradients are those areas that contain electrical equipment or equipment directly connected to electrically grounded equipment and where animals are exposed to more than one electrically conductive element, including concrete, water systems, feeding systems, manure handling systems, milking systems, stalls, pens, or crates and any other condition where a potential for stray current between elements exists.

Concrete floors and slabs must have embedded elements installed in all areas in which animals may contact other potential planes or other conductive elements. Reinforcing elements in slatted floors will not be required to be individually bonded where these slat panels are supported by conductive structure that is part of the equipotential plane.

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