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Stray voltage: What is it and what can be done about it?

Progressive Dairy Editor Karen Lee Published on 17 January 2020

Dr. Phil Meadows describes stray voltage as a black box.

As a practicing veterinarian at Mitchell Veterinary Services in Mitchell, Ontario, he said, “When there are problems on dairy farms, there are a lot of boxes I can check off and questions to ask about this or that.



When it comes to all the boxes being checked, and I still can’t figure it out, then it is, ‘Well, maybe it is stray voltage.’”

To better troubleshoot stray voltage scenarios, Meadows is a member of the Ontario Uncontrolled Electricity Working Group (UEWG). He presented on the topic and what can be done to decrease the levels of stray voltage at the Progressive Dairy Operators Triennial Symposium last March in Toronto, Ontario.

While most people understand stray voltage to be a low-level electric shock that can produce a sensation or annoyance in farm animals, the Institute of Electrical and Electronics Engineers (IEEE) has defined it as a voltage resulting from the normal delivery or use of electricity which may be present between two conductive surfaces that can be simultaneously contacted by members of the general public or their animals.

“If you are going to deliver electricity, you are going to have stray voltage,” said Muayad Tarabain, team engineer on Hydro One’s farm rapid response team, who presented this information alongside Meadows.

“It’s about controlling and not totally removing it,” he said.


Other key points to the definition are the presence of two conductive surfaces, such as metal, water or the floor, with simultaneous contact. If the points are found to be on opposite ends of the barn that a person or cow cannot be in contact with at the same time, it does not meet the definition of stray voltage, Tarabain explained.

In the early 2000s, the Ontario Energy Board (OEB) hired Dr. Doug Reinemann, professor of biological systems engineering at the University of Wisconsin – Madison, to review scientific research on stray voltage.

Based on that information, the OEB changed the distribution systems code in 2009 to include stray voltage testing procedures and a limit of 2 mA with 500 ohms resistance at cow contact point.

“From then on, that’s what Hydro One and all of the other distribution companies have used as an allowable limit at cow contact,” Meadows said.

Mitigation techniques

There can be a lot of deficiencies in the system that could cause the amount of current flowing through the animal to be higher than desired. These deficiencies can be on the farm or on the utility side.

On the farm, Tarabain said, a good place to start is the neutral wire. Look to see if there is any insulation burning out on the neutral wire or any defective wire connections.


“Barns are a very hostile environment for anything electrical. It is a very corrosive environment, and connections will age much quicker than if they are outside in open air,” he said.

Other deficiencies can be found due to a lack of proper grounding, insulation peeling off phase wires, an imbalance of 120-volt loads, equipment problems or any other poor or faulty wiring.

While not a stray voltage problem by definition, Tarabain mentioned poor wiring of electric fences or trainers can also create a problem that has very similar symptoms to stray voltage.

If no deficiencies are found, and stray voltage is above the threshold, then system improvements may be necessary. Switching to a three-phase service is really effective if the option is there and the farm already has a large demand on the service. Another effective option is to upgrade the neutral wire size.

The new electrical code requires new buildings to have a four-wire system with separate neutral and ground wires. Making this change to an existing building can be effective in reducing stray voltage. If building a new barn, Tarabain said it would be good to consider equipotential bonding.

The mitigation techniques are similar on the utility side of the system. Technicians will investigate defects on the neutral wire and connections, look for poor grounding and any system imbalances. They can also consider improvements like three-phase expansion and upgrading the neutral size.

As a last resort, he said the utility can isolate the two systems so the farm equipment will no longer be directly connected to the utility system.

“If you do any isolation inside your barn, that’s up to the electrician you hire – but if it’s going to happen at the utility transformer, it has to be done by us,” Tarabain said. “There’s a lot of limitations on when we can do that. It is sometimes a solution of last resort, and it comes with a lot of risk.”

Where to start

Dairy producers who want to investigate on their own can use a troubleshooting guide from the Electrical Safety Authority.

When the utility company is involved, the OEB regulation outlines a process with up to three phases.

  • Phase 1 – Determine if there is a stray voltage problem at the property.

  • Phase 2 – Measure the contribution. If that contribution is above a 0.5-volt contribution limit on the utility, then they are responsible for fixing their system.

  • Phase 3 – Repeat testing to confirm it is below the threshold.

For Hydro One customers, Tarabain explained that each phase might require several site visits. They measure the entire barn to find the worst location and then set up recording equipment for two to three days.

“Most of the time, the maximum isn’t going to be when we are there but rather in the evening or morning milking time,” he said.

They analyze the data and share it with the farm. If the measurements are above threshold, they will work on their system and then come back for testing to verify the results.

“The price for all of this to you is zero,” Tarabain said for Hydro One customers. “You are not required to hire an electrician. You don’t have to do that on-farm before you call us. If you believe you have a stray voltage problem on your farm, you call us, we do all this testing, and it’s at no cost to you.”

From September 2016 through December 2018, Hydro One completed 165 farm investigations, with almost 75% of them on dairy farms.

After testing, 89% of the cases were under the OEB threshold. Eighteen cases were above the OEB threshold, and all but one was above the utility contract threshold, where they had to take action to resolve the problem.

The farm locations were spread throughout Ontario. “It’s not like there is one bad area and one good area,” Tarabain said.

Working group actions

As the UEWG continues its mission to advocate for improved mitigation of uncontrolled ground current and voltage as it relates to Ontario farms, Meadows said it is looking to update the literature review to see if current research suggests a change to the OEB threshold.

They also want to work with the Electrical Safety Authority to create a standardized stray voltage testing method for all electricians to follow when on-farm.

Stray voltage will always exist in an electrical system, but finding ways to control it and monitoring the thresholds will limit the effect it has on farms.  end mark

Karen Lee
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