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Understanding Stray Voltage

​What's new?image of four cows in a field
Hydro One has recently formed a new Farm Rapid Response Team to help identify, assess, and mitigate stray voltage problems.​​​​​​​​

What is stray v​​oltage?
From the normal delivery and use of electricity, a small voltage may exist between two conductive surfaces that can be simultaneously contacted by an animal. Examples of the conductive surfaces include concrete floors, metal stabling, milk pipelines, water bowls, etc. 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's an acceptable level of stray voltage?
A great deal of research has been conducted over the past 40 years on the effect of stray voltage on farm animals. The Ontario Energy Board (OEB) has completed a comprehensive review of this research in order to determine the rules and regulations that govern stray voltage. The OEB indicates that stray voltage, measured in animal contact voltage, must not exceed 1.0 volt and if exceeded the electricity distributor must proceed with further testing to determine if its system is contributing to more than 0.5 volts to the overall animal contact voltage level.

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 Authority(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 cell count
  • Lowered milk production.
These symptoms and effects 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.

What is Hydro One doing to help prevent stray voltage?
We perform a number of measure to help prevent stray voltage.​ Some measures include ensuring the neutral and grounding systems are in good working order, balancing loads and upgrading the neutral conductor of the supply system.


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: 
  • Call our Farm Rapid Response Team at 1-888-405-3778, Monday to Friday from 8:30 a.m. to 4 p.m. 
  • Complete the Stray Voltage Investigation Form.
  • Email, fax or mail the completed form to us.
A​ttn: Farm Rapid Response Team
Hydro One Networks Inc.
483 Bay Street, 6th Floor, South Tower
Toronto, ON M5G 2P5
Fax: 416-345-5957​

Please note: Before we can begin an investigation, we must receive your completed form. We'll call you within five business days, after we receive your investigation form to arrange a site visit.

Hydro One's Farm Stray Voltage Investigation Process
Farm Stray Voltage Investigation Process

Do I need to hire an electrical contractor?
You may also hire an electrical contractor that can help identify on-farm sources of stray voltage. We recommend your electrician download our Stray Voltage Test Procedure for Electrical Contractors. This will help your electrician diagnose any issues on your farm and it will also provide useful information if further investigation is required.

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:  En​glish | Frenc​h
Stray Voltage Fact Sheet:  EnglishFren​ch 

Dispute Resolution Process
If you have a complaint, please call us at 1-888-405-3778, Monday to Friday from 8:30 a.m. to 4 p.m. If we can't resolve your complaint, it will be escalated to our Customer Relations Centre for resolution. In the event that issues can't be resolved to your satisfaction, your complaint can be escalated to the Ontario Energy Board.
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