Electricity, one of the most versatile and widely used power sources, is used extensively on almost every farm. Farmers are so familiar with electricity that they may take electrical safety for granted. When this happens, accidents often follow. The National Safety Council reports more than 800 electrical fatalities annually. On average, more than 40 of these deaths are directly related to farming operations.
How much electricity is fatal? People can feel electrical currents at levels as low as approximately 1 milliamp (mA), which produces a slight tingling sensation. Increasing current levels above the 5 mA "let go" threshold can cause loss of muscular control, irregular heart rhythm and, finally, cardiac arrest. Five mA is only a small fraction of the current needed to power a 60-watt bulb, which draws about 1/2 amp, or 500 mA.
Electrical shock occurs when a person touches an electrically charged object at the same time they are touching another surface capable of conducting electricity, such as the ground. A current then passes between the points of contact. The shock effects depend on the amperage, duration of contact and resistance of the pathway through the body. For example, damp skin is less resistant to current flow and permits greater shock effects. For this reason, you should work in a dry environment while handling electrical equipment.
The seriousness of a shock depends on the path the current takes through the body. For example, a small current passing through the heart is much more critical than a current passing between two fingers of the same hand. Testing for live current with one hand instead of two reduces the risk of a dangerous shock by making current less likely to flow through the heart.
Recognize that power lines often follow property lines. As workers reach the end of the field and turn the equipment, there is a good chance power lines will be nearby. Power lines also are often near grain and equipment storage facilities. Be sure that paths from equipment storage areas to fields and from the fields to grain storage areas are safe routes. If you have any doubts that your equipment will clear a line, assume that it will not and take measures to avoid possible contact.
Crop storage equipment such as balers and stackers can be extended in height to exceed electric code clearances for power lines. When storing hay or baled straw, take precautions to be sure the stacking equipment will not come into contact with power lines.
Portable grain augers are a leading cause of farm electrocutions. Lower augers when moving them from one bin to another. The operating height of an auger usually is greater than the height of power lines. If workers hand-push one into a line, they will be instantly electrocuted.
Stray voltage on farms may stem from several sources. The voltage may occur predictably throughout the day, or it may occur randomly. These factors make controlling stray voltage a major problem.
On-farm stray voltages have been traced to the following sources:
Electrical motors and equipment can "short out" or ground fault to their outside casings. The severity can vary from a fault with no visible effect to a complete short circuit. When short circuits occur, all conductive materials, such as stainless steel milk lines and pipe fencing, become energized. Wood also can conduct electricity when it is wet. To correct the problem, faulty equipment should be repaired or replaced immediately by someone with proper training. The three-wire electrical supply line helps reduce the problem when the fault first occurs.
Voltage gradients through the earth or across a floor occur when an underground wire faults to earth. This often happens when the insulation of underground wires not rated for direct burial becomes damaged. Typically, the wires have not been buried at the proper depth. Underground wires buried many years ago are suspect, particularly if voltage gradients are detected in the earth. To correct the problem, the lines must be replaced with ones rated for direct burial.
Electric fence wires running through buildings can cause problems when building electrical wire is used. The maximum insulation rating of building electrical wire is 600 volts, which is not adequate insulation for the high voltage pulse output of a fence charger. When this type of stray voltage is suspected, look for breakdowns in the insulation that could be causing a fault to metal equipment inside a barn. To prevent this problem, use insulated wire rated beyond the maximum voltage output of the fence charger.
MU publications with further information on electrical safety include G01020, Lightning Protection for Missouri Farms and Homes, and G01406, Preventing Shocks to Cows in Milking Parlors.
Publication #: G1934
This document is apart of a series from the University of Extension, University of Missouri-Columbia. If you have special needs as addressed by the Americans with Disabilities Act and need this publication in an alternative format, write ADA Officer, Extension and Agricultural Information, 1-98 Agriculture Building, Columbia, MO 65211, or call (314) 882-8237. Reasonable efforts will be made to accommodate your special needs. Publication date: October 1993.
Partial funding for this publication was provided by the University of Missouri-Columbia/National Institute for Occupational Safety and Health Cooperative Agricultural Promotions Agreement U05/CCU706084-01.
David Baker and Rusty Lee, Dept. of Agricultural Engineering, University Extension, University of Missouri-Columbia, Columbia, MO 65211.
Disclaimer and Reproduction Information: Information in NASD does not represent NIOSH policy. Information included in NASD appears by permission of the author and/or copyright holder. More