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Understanding Stray Voltage

image of four cows in a field
What is Stray Voltage?

Varying amounts of low-level voltage may exist between the earth and electrically grounded farm equipment such as metal stabling, feeders, or milk pipelines. This voltage, known as animal contact voltage, stray voltage or tingle voltage, usually presents no harm. However, if the voltage level is high enough, it may affect livestock behaviour and health.

What causes Stray Voltage?

Stray voltage can be caused by a wide variety of off-farm and on-farm sources:

Off-farm sources
In a properly functioning electrical distribution system, some voltage will always exist between the neutral system (ground conductors) and the earth. The level of this neutral-to-earth voltage (NEV) can change on a daily or seasonal basis, depending on changes in electrical loading, environmental conditions and other factors such as improper grounding and neutral connections. For safety reasons, Hydro One’s neutral system is connected to a farm’s grounding system. While this bond protects people and animals from shocks caused by faulty electrical equipment and lightning strikes, it can also result in a stray voltage equal to a fraction of the NEV appearing on grounded farm equipment, such as feeders, waterers, metal stabling, metal grates and milk pipelines.

On-the-farm sources
Poor or faulty wiring, improper grounding and bonding, unbalanced farm loading, overloaded circuits or panels, defective equipment or voltage from telephone lines or gas pipelines are all possible sources of stray voltage. By ensuring your system meets Electrical Safety Association (ESA) standards, you can eliminate many stray voltage problems.

What are common signs of stray voltage and how does it affect livestock?

Reported symptoms for dairy cows include:

  • Reluctance to enter the milking parlour
  • Reduced water or feed intake
  • Nervous or aggressive behaviour
  • Uneven and incomplete milkout
  • Increased somatic count
  • Lowered milk production.

These symptoms can also be the result of other non-electrical farm factors such as disease, poor nutrition, unsanitary conditions or milking equipment problems. Farmers should consider and investigate all possibilities, including stray voltage, when attempting to resolve these symptoms.

infographic demonstrating how a dairy cow could be affected by stray voltage within a barn 


If you think you have a stray voltage problem

If you believe that you have a problem with stray voltage, please call our Customer Communications Centre at 1-888-664-9376. Our Customer Communications Centre will arrange for our local field business centre to call you within five business days to arrange a site visit. You will need to complete aStray Voltage Investigation Form and provide it to our field business centre.

To help determine if you have stray voltage, we suggest you hire a licensed electrician. We recommend your electrician download ourStray Voltage Test Procedure for Electrical Contractors to help diagnose any issues on your farm.

For more information

For additional information on the effects of stray voltage on livestock, see:

 Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) website
 Electric Power Research Institute - Overview of Stray Voltage
 Stray Voltage Test Procedure for Electrical Contractors

Stray Voltage Investigation Form:  English
Stray Voltage Fact Sheet:

Dispute Resolution Process

Initial contacts for customer complaints should be made by calling Hydro One at 1-888-664-9376 during normal business hours, Monday to Friday from 7:30 a.m. to 8 p.m. E.T. Customer complaints that cannot be resolved by calling this number will be escalated to Hydro One’s Customer Relations Centre (CRC), which will serve as the primary point of contact with Hydro One. A member of the CRC will make contact with the customer, coordinate internal complaint activities, research, investigate, and follow up (when necessary) on the complaint to ensure resolution and closure.

In the event that issues cannot be resolved between Hydro One and the customer, complaints can be escalated to the Ontario Energy Board.

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