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Stray Voltage Exposure |
| Q.
If stray voltage is in the environment, does that mean that cows are always experiencing it? |
| A.
Not necessarily and not all the times. For a cow to actually experience stray voltage a number of circumstances must be present; this is called exposure. Just like the case of exposure to a virus, stray voltage exposure requires source, proximity, and mechanism. If any of these three requirements is missing, there is no stray voltage exposure. We may think of exposure as hanging from a chain of three links. If any link in the chain is broken, there is no exposure.
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For the case of stray voltage, source, proximity, and mechanism are defined as follows:
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- Source — a power system. The power system that is the source of the current in question must be positively identified. This can be difficult, because the power system currents are many and varied, and commingle in the earth with those of other sources. Identifying the power system requires verifying a direct connection between it and the observed current.
- Proximity — stray voltages where the cow lives. Stray voltages must be present where the animals are, and strong enough to affect animals. For dairy cows, the best and most recent knowledge from stray voltage research tells us that herd health and milk production are not affected by less than two or three volts. Allowing for a conservative margin of error, a dairy farmer should be concerned about stray voltages above approximately one volt.
- Mechanism — two-point contact. A cow must make contact with at least two points on the earth simultaneously (one of the points may be a metallic object connected to the earth). A single-point contact does not allow for a loop circuit situation, necessary for current to flow, and is not stray voltage in the precise way we address it here. A single-point contact, therefore, means there is no exposure to stray voltage.
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When all three conditions are met simultaneously, there is stray voltage exposure and the cow will experience current flowing through its body. Whether the cow will even feel the current depends on many other circumstances such as the cow's susceptibility to current and the contact resistances that limit current flow.
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