Beyond simple aesthetics, Grandpa’s dairy barn had something else going for it.
The wooden framing, stalls and mangers didn’t conduct electricity, so the cows inside were never disturbed by stray voltage.
Today, modern dairy barns built on reinforced concrete pads, steel stanchions and covered with metallic sheathing have created an environment where cows can get a tingle now and then.
That’s because manure and moisture can corrode electrical systems, leading to leaks. Problems can arise with as few as two volts, which may lower milk production and make cows restless and fearful at milking time.
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Elevated somatic cell counts that can’t be attributed to other factors are one indication of stray voltage, said Ray Boris of Manitoba Hydro.
Also, stress from tingle voltage can delay milk letdown time, leading to retained residual milk in the udder, which represents lost production.
It can also lead to more cases of mastitis caused by higher milker vacuum as the machine puts more pressure on the teat to draw milk out.
If cows come in contact with stray voltage running through the water lines every time they drink, soon their little problem becomes a big headache for the farmer.
“Cows have a much lower resistance to current than humans. The resistance of a cow typically ranges from 300 to 900 ohms, while the resistance of a person ranges from 3,000 to 9,000 ohms,” said Boris.
Cows are heavier and their four hoofs provide good contact with the ground, he added.
“Compare their situation to a man with dry socks, rubber boots and calloused hands. Under these conditions, the man may not even detect a current flow, while the cow may experience noticeable discomfort.”
Sources of stray voltage can be common electrical shorts in equipment, defective underground cables and missing or inadequate grounding systems. In once case it was traced back to a spider web that, when wet, closed a connection to a metal stanchion.
It can also originate from neutral-to-earth voltage, which is a normal and unavoidable consequence of operating electrical equipment on the farm.
“For example, a cow standing on the floor of a barn has its hoofs in good contact with true ground through the concrete.
“When a cow drinks from water bowls, which are grounded through the plumbing system, the animal makes a connection between the neutral conductor and true ground,” said Boris.
“If ground potentials are different, current will flow through the cow.”
Boris said stray voltage is best avoided by constructing the milking parlor on an “equipotential plane,” using a small metal grid welded on top of the rebar in the concrete floor that is connected to all metal stanchions and troughs that cows come into contact with.
For barn owners who suspect that stray voltage might be a problem, he advised having an electrician take voltage measurements. Manitoba Hydro has published a guide to assist electricians in measuring stray voltage in dairy barns, he added.
If a problem is discovered, retrofitting an existing barn with an equipotential plane can be accomplished by cutting grooves in the floor with a concrete saw and installing No. 6 bare copper wire in a grid pattern, which is then filled with fast-curing grout.
At minimum, the wires should be bonded at each end of the barn and to all metal structures with which cows come in contact.
Other more expensive solutions involve replacing the concrete floor with one incorporating the equipotential plane, or capping the floor with a new 10 centimetre layer of concrete to cover the steel mesh.
