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Understanding Stray Voltage 

What is Stray Voltage?

 Varying amounts of low-level voltage often exist between the earth and electrically-grounded farm equipment such as metal stabling, feeders, or milk pipelines. Usually, these voltage levels present no harm to animals. However, if an animal touches a grounded metal object where these low
voltages are found, a small electric current may pass through the animal. The voltage that causes this small current is known as “animal contact voltage,” “stray voltage” or “tingle voltage.”

Reported symptoms for dairy cows include:

  • Reluctance to enter 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 nonelectrical 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.

What causes stray voltage?

Stray voltage can be produced 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. 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 farm wiring, improper grounding, unbalanced farm system loading, defective equipment or voltages from telephone lines or gas pipelines are all possible sources of stray voltage.

If you think you have a stray voltage problem

First you will have to hire a licensed electrician to test for stray voltage. If this testing by the electrician confirms that there is a stray voltage problem, call our Customer Communications Centre at 1-888-664-9376 (Monday to Friday, 7:30 a.m. to 8 p.m.) with the name and telephone number of the electrician who performed the test. 

Your local field business centre will call you within five business days to arrange an appointment.  


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 Fact Sheet:
 English |  French 


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.