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Stray Electricity is Still Around

Dairy Pipeline: October 1997

by Jerry Jones
Extension Dairy Scientist, Milk Quality and Milking Management
Virginia Tech

Even prior to my return to Dairy Science in July, I received several calls about stray voltage on dairy farms. I have used a threshold of 0.5-0.8 volts or 2-3 milliamps at which cows' behavior becomes sensitive to voltage. Cows are reluctant to enter the milking parlor and when they do, they are uneasy (they dance around even when music isn't being played). Feed consumption may be reduced. Milk yield is usually depressed; perhaps because cows don't milk out or take longer to milk. Somatic cell counts and clinical mastitis probably increase. You can usually find many of these symptoms in affected herds but these symptoms can be caused by things other than stray voltage. The source may originate on the farm from problems with wiring, motor faults, etc., such as electric fences, faulty fluorescent lights, telephone grounds, watering systems, silo unloaders, unbalanced neutral loads, bulk tanks, and many others. Off-farm sources include utility company grounds and neutrals, farm located at the end of transmission lines, and faulty grounds from adjoining properties. To check for stray voltage, you need a voltmeter with an AC voltage scale. Also, it should read voltages to the nearest 0.1 volt at loads between 0 and 5 volts, such as a digital volt meter. For details on how to check for voltage, request a copy of Dairy Guideline 404-250, Stray Electricity on Dairy Farms from your county Extension office, my office or consult your milking equipment dealer, veterinarian, or milk plant field rep for assistance. If you find voltage, check with one of these people as to how you correct it. If building new or revising old facilities, take precautions to try and prevent stray voltage problems, such as including an equipotential plane (this means ground everything in some organized fashion) and/or an isolation transformer or some sort of blocking device.

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