Stray voltage

Stray voltage is a low level of voltage that animals may encounter in their normal activities. If an animal simultaneously contacts two surfaces with a voltage difference, a small electrical current can flow through the animal. A common example is when an animal touches both an electrically connected point (watering cup) and the concrete floor (earth).

Stray voltage is a naturally occurring phenomenon due to the operation of farm electrical systems and utility distribution systems. A small amount of stray voltage will be present with all properly grounded electrical systems. Any metallic structure or surface may become a pathway for electrical current carried on the neutral and grounding systems.

The sources of the current or voltage may be on-farm, off-farm or a combination of the two. In many cases, there is more than one source. Some sources may include:

• Equipment ground faults
• Improper separation of equipment grounds and neutral wires in buildings
• Excessive voltage drop on the electric system neutral wires
• Improperly installed electric fencers and trainers

An avoidance behavior can occur when an animal comes into contact with stray voltage at a level that it can feel. At higher voltage levels, behavior changes can be severe enough to limit milk production or growth in livestock.

The Public Service Commission of Wisconsin has determined that if a voltage difference of 1.0 volt AC or more between animal contact points (measured with a 500-ohm resistor in the circuit), action should be taken to reduce this voltage.

To calculate the current that may flow through an animal, a resistor is placed in the testing circuit where the animal would be and voltage is measured across it.

A standardized measurement of stray voltage is defined as "the voltage measured across a 500-ohm (nominal) resistance connected between two animal contact points."

The 500-ohm resistor is used to simulate the worst case or lowest resistance of the animal circuit.

While stray voltage can never be completely eliminated, you can take steps to reduce the levels.

Use our stray voltage checklist.pdf to identify potential trouble spots and evaluate your electrical system with the Stray Voltage Detection: A Self-Help Guide.pdf, published by the Midwest Rural Energy Council.

In addition, you can request a stray-voltage investigation by your Alliant Energy Agricultural Representative. The rep will determine the causes of the stray-voltage levels on your farm.

If cow-contact voltages are due to the wiring on your farm, your Agricultural Representative will offer consultation to you and your electrician.