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Equipotential planes in livestock confinement areas


March 2, 1998

The Board of Electricity will enforce the following with regard to the type of animal: The term "animal" includes all poultry, livestock, fish, or similar creature. "Poultry" refers to birds raised or kept for food or breeding purposes. "Livestock" refers to cattle, hogs, sheep, goats, horses, and similar animals raised or kept for food, breeding, or pleasure purposes.

Applicability: The 1996 National Electrical Code® (NEC) identifies the applicability of this article to poultry, livestock, and fish confinement systems. Subpart (a) of Section 547-8 applies to livestock or poultry confinement areas, whereas Subpart (b) applies to only livestock confinement areas. This subpart applies to confinement areas and is not restricted to areas within buildings, but also applies to confinement areas located outdoors.

1996 NEC Section 547-8 (b). Concrete Embedded Elements. Revision. Wire mesh or other conductive elements are now required to be installed in the concrete floors of livestock confinement areas and must be bonded to the grounding electrode system of the structure or area served to provide an equipotential plane with a voltage gradient at entrances and exits regularly used by livestock. Previously in the 1993 NEC, establishing an equipotential plane was optional, whereas the 1996 NEC makes it mandatory. Providing an "equipotential plane" will prevent a difference of voltage from developing and subsequently causing abnormal animal behavior or productivity. "Voltage gradient," as used in this section, refers to a condition where there is a gradual increase or decrease from one potential plane to another. A voltage gradient allows animals to move from the equipotential plane, required to be established in the confinement area, to adjacent areas without experiencing electrical shock sensations. One method to establish a voltage gradient is to install ground rods on one foot centers at a 45° angle outward from vertical, with the upper end extending from, and bonded to, the equipotential plane. The means of bonding to conductive elements shall be by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means.

Note: "Voltage gradient," as used in this section, can be compared to using a ramp between different levels, much like a ramp is used instead of a stairway.

The bonding of conductive elements in concrete floors and adjacent conductive elements must be accomplished as follows:

1. Concrete floors, walls, and footings that are in direct contact with the earth must contain conductive elements that are effectively bonded together and be either reinforcing steel or mesh, or bare copper conductors not smaller than #8. Unless an electrically engineered design requires or allows otherwise, conductive elements must be installed a maximum of 12 inches on center across concrete floors, walls, and footings. Isolated reinforcing elements located in slatted floor panels will not be required to be bonded where the slat panels are supported by concrete structure that contains bonded elements that are a part of an equipotential plane.

2. All conductive equipment, structures, or surfaces that are accessible to each other and from a concrete floor of a confinement area must be bonded together to create an equipotential plane. The term "confinement area" includes areas that are located outdoors without structure, such as feeding floors and holding areas. Confinement areas that do not contain electrically supplied equipment or systems that are connected to an electrical equipment grounding conductor system are not required to comply with the requirements of Section 547-8, although they may require a voltage gradient from an adjacent equipotential plane.

3. Inspection of bonding methods that become encased in concrete must be made before the concrete is poured. Minnesota Rules 3800.3770 requires wiring concealed without inspection to be exposed to enable the required inspection to be performed. It is the responsibility of the installer of the wiring to notify the inspection authority sufficiently in advance to allow the inspection to be completed before wiring is concealed in any manner.

For more information refer to the latest edition of EP473, published by the American Society of Agricultural Engineers (616) 429-0300

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