What is 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.

What causes stray voltage?

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

How can stray voltage affect an animal?

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.

How is stray voltage measured?

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.

How can I prevent stray voltage?

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.

Evaluate your electrical system with the Stray Voltage Detection: A Self-Help Guide [PDF], published by the Midwest Rural Energy Council.

Contact the Business Resource Center at 1-866-ALLIANT (866-255-4268) to request a stray voltage consultation. 

What does a stray voltage consultation include?

• Spot voltage checks at animal contact locations to pinpoint where an animal may be exposed to voltage and to determine locations for extended time recording.
• Voltage measurements over a minimum of at least two milkings or approximately 24 hours on the utility electrical system, the farm electrical system and at animal contact locations. Animal contact voltages measured with and without a 500-ohm resistor to ensure accuracy.
• We evaluate both the on-farm and off-farm systems. We can show the measurements from both systems to you.
• Monitoring continues until it is determined that the entire electrical system has been evaluated and the concerns of the customer addressed.
• You will receive a summary letter and an explanation of all the data collected.

What happens after the consultation?

If the animal contact voltage measured is higher than the preventative level of action, additional tests may be performed to determine the source of the voltage. If our utility system is contributing 0.5 volts or more to the animal contact voltage level, we will modify our equipment to lower this voltage below 0.5 volts.

If the animal contact voltages are due to the wiring on your farm, our consultant will assist you in identifying the sources and work with your electrician to remedy the trouble spots.

Our representative can also perform follow-up testing to determine the effectiveness of any modifications. He or she will also consult on new construction projects or the installation of equipotential planes.

Can you install a neutral isolator on my farm?

Yes, within the guidelines of the two different procedures:

• The first procedure determines that the stray voltage level at the animal contact point is above the level of action and is caused by an off-farm electrical source. This is a temporary installation which will be removed when the voltage has been lowered below the level of action.
• The second procedure allows you to request a neutral isolator be installed without regard to the animal contact voltage. There are costs for this type of installation.