Understanding Stray Voltage
Stray voltage, also known as neutral-to-earth voltage or touch potential, refers to the presence of electrical voltage between two conductive surfaces that a person or animal may come into contact with. While not inherently dangerous, stray voltage can cause nuisances or discomfort in some cases. By understanding what causes stray voltage, where it occurs, how to detect it, and strategies for mitigation, farmers, electricians, and other professionals can address this issue effectively.
What Causes Stray Voltage?
Stray voltage typically arises from electrical systems and equipment on farms and in other rural settings. It occurs when there is a voltage difference between two surfaces that should be at the same electrical potential. This often results from improper grounding, faults in wiring, or other deficiencies in electrical systems.
The most common cause of stray voltage is neutral-to-earth voltage originating from grounded electrical systems. In a properly functioning system, the neutral wire should remain at or near zero volts. However, resistances or current flows to earth can cause the neutral to deviate from zero volts, leading to a potential difference between surfaces the animal contacts.
Several factors can contribute to these neutral-to-earth voltages, including poor connections, undersized neutral conductors, high resistance grounds, imbalanced loads, and faults in appliances. Systems with long runs of underground wiring and multiple buildings are particularly exposed to such issues.
In addition to grounded-neutral sources, stray voltages can also arise between two metal surfaces that become energized. This can occur due to:
Capacitive Coupling
Nearby energized conductors can induce a voltage in the trough through electromagnetic fields, even without a direct connection.
Ground Potential Rise
Faults in the electrical system may cause the ground to have a higher voltage relative to the neutral, creating a measurable difference.
Leakage Currents
Nearby electrical installations can generate leakage currents that flow through the ground, leading to voltage differentials.
Electromagnetic Fields
The presence of electrical equipment nearby can produce electromagnetic fields that induce stray voltage in conductive surfaces.
By understanding these causes, farmers and electricians can take proactive measures to identify and mitigate stray voltage issues effectively.
Where Does Stray Voltage Occur?
Stray voltage is usually only an issue in agricultural and rural settings. Farms often have extensive wiring spanning long distances between multiple buildings. The scale and complexity of these systems increases susceptibility to stray voltage.
Some common locations where elevated voltages may be detected include:
Water bowls and feeders
Milking equipment
Metal floors and stanchions
Fences, gates, and water lines
Barns, sheds, and other outbuildings
The presence of wet manure or soil helps conduct stray voltages to surfaces animals contact. Any area where livestock spend significant time and have simultaneous contact with two conductive surfaces could potentially have elevated voltages.
How is Stray Voltage Detected?
Detecting and measuring stray voltage requires specialized instrumentation and procedures. Voltages are often very low, in the range of millivolts or a few volts. Subtle issues with wiring or grounds can lead to nuisance voltage levels.
To properly characterize a stray voltage problem, testing is needed during normal operations when voltages are present. A technician uses a voltmeter with high input impedance to avoid drawing down voltages during measurements. Testing points include possible animal contact points like water bowls, floors, and milking equipment.
The technician records variations in voltages over time at each location as equipment switches on and off. Noise filters are often needed to isolate the low-level steady stray voltages from normal fluctuations and spikes. Careful testing protocol is required to distinguish between normal electrical noise and problematic voltages.
Portable data loggers provide long-term voltage monitoring at multiple points. The detailed voltage records help pinpoint origins and patterns of stray voltages occurring on the system.
