Basic Measurement Procedures

Voltage is very easy to measure and voltage is probably the most reliable first indicator of a stray voltage or current problem. There are two ways to measure voltage:

  1. Point-to-point and
  2. Point-to-reference ground.

In the point-to-point method, measurements are simply made between two points which may be contacted, simultaneously, by an animal.

In the point-to-reference ground method, one of the two measurement probes is connected to a reference ground. This is more useful in identifying specific sources, and it's repeatable.

Either measurement technique requires a good electrical contact between the instrument probes and the points of contact. Generally, a metallic surface should be scratched with the probe. When the floor is one of the points of contact, a 16- to 36-square-inch metal plate should be used to make contact with the floor. To ensure good electrical contact, the floor and metal plate should be wet.

The second requirement is that the investigator be able to reliably estimate the current-producing capability of the voltage source. Remember, cows respond to the current generated by a voltage and not to that voltage directly. A general measurement / exposure circuit includes source, pathway, contact, and body impedances. Quantifying or reproducing the actual values of each impedance is not feasible under field conditions. Therefore, determining the current producing capability must be done through other means.

When a device with high impedance such as a voltmeter is placed in a circuit, the voltage reading alone won't indicate the current producing capabilities of the source. In point-to-point measurements, get a second voltage measurement with a resistance (impedance) simulating that of an animal placed across the leads (probes) of the voltmeter (perhaps 500 ohms). Only then will you be able to estimate the actual cow contact voltage.

Just keep in mind, body impedances of cows vary and metal-to-metal contact resistances of the measurement circuit will likely be very different from the actual contact resistances of an animal, hooves to floor, or body to stanchion. These differences mean the measured voltage may be somewhat different from the voltage the animal actually experiences.

This is actually an overly simplistic description of the point-to-point measurement
technique. To ensure proper measurements, an investigator must thoroughly understand
stray voltage issues.