Neutral-to-earth voltage (N-E), sometimes called “stray voltage,” is a condition that results when an electrical current flows through a neutral conductor. Most (110 volt) electric lines contain three wires- one “hot” or powered, one neutral and the ground wire. Traditionally, the hot wire is black and the neutral white. Normally, electricity flows through the black wire, through the device to be powered and returns to the source through the neutral (white wire).
Stray voltage occurs when electricity “leaks” from the black wire directly to the white or ground wires before passing through the device to be powered. These leaks produce only small amounts of electricity. Direct contact between the white and black wires would “short” the system and blow a fuse or circuit breaker.
Stray voltage can result from arcing at equipment connections, frayed insulation and other mechanical problems. In addition, multiple grounds that are not interconnected can create ground currents capable of shocking livestock. Leaks and non-connected ground systems create electric charges in the earth that aren’t normal when an electric system is operating properly.
When these ground-based currents are present, animals or persons that contact well-grounded equipment-such as metal stanchions or metal fence posts-will receive a shock as the electricity passes through their bodies. These N-E voltages, though rare, exist on all devices and are most common on farm feeding and milking equipment.
Neutral-to-earth voltage is present in nearly all farm electrical systems. It is an inherent part of the system and can never be entirely eliminated.
Dairy cows -- because dairy farms use sophisticated machinery that demands large amounts of electricity -- are most affected. N-E voltage has also been known to affect swine farrowing units as well as poultry and beef operations.
Voltages ranging from one volt and above can cause potential problems. Even those between one-half and one volt may affect some animals.
Dairy cows exposed to neutral-to-earth voltage can exhibit three general types of symptoms:
- Hesitate or refuse to approach certain waterers, feeders, or metallic equipment.
- Hesitate to enter parlor or jump across transition joints.
- Tread, kick, or appear nervous while milking.
- Increased defecation and/or urination in milking parlor.
- Reluctant to consume water or feed.
- Poor milk letdown and incomplete or uneven milkout (leaving abnormal amounts of residual milk in one or more quarters).
- Increased milking time.
- Increased mastitis.
- Lowered milk production.
It is important to remember, however, that these conditions may be caused by sources other than N-E voltage. These include poor milking practices, improperly sized or malfunctioning equipment, improper feed, poor herd health or poor herd management. All possible causes should be examined to determine the appropriate corrective procedure.
Neutral-to-earth voltage can be caused by a number of factors, both in and around the farm. The amounts of minerals and moisture in the soil, subsoil and rock strata, and the varying water table level can affect any grounding system and change N-E voltages. Sudden problems are usually due to electrical loads, conductors and connections.
Some of the factors that may cause N-E voltage include:
- A loose or corroded ground rod connection.
- Badly rusted electrical boxes or conduit (a tube or duct for enclosing electric wires or cable).
- Wires, electrical boxes, or motors in wet or damp areas.
- Accumulation of dust on or around electrical equipment.
- Bent or broken conduit.
- Scraped insulation, exposing wires.
- Insulated wires wrapped around metal pipes.
- Electrical boxes missing covers, or covers that are loose.
- Loose, hanging wires.
- Electrical outlet missing third hole for ground.
- Unbalanced electric load.
- Pinched pulsator wiring.
There are several things you can do to try to reduce neutral-to-earth voltage. Keep in mind, though, that some N-E voltage will always exist in electrical systems.
If the problem originates on the farm:
- Upgrade electrical system.
- Replace faulty equipment that may produce leakage currents.
- Install heavier equipment grounds or adequate power circuits.
If the problem originates off-farm:
- Always consult with your power supplier to work out a safe and effective solution.
- Installation of an isolation transformer on the farm may be advised - you will then assume responsibility for maintaining a proper neutral ground on the farm.
If the problem originates on and/or off-farm:
- Provide an “equipotential plane” in milking parlors as a way of eliminating the possibility of current flowing through a cow’s body.
Remember that a number of stress factors can result in decreased milk production. Therefore it is important to isolate and correct ALL causes. To accomplish this, a team approach is recommended.
- Keep a notebook detailing problems that occur. Include the time of day, equipment in use, duration and a description of the cow’s reaction.
- Have appropriate professionals thoroughly check your herd’s health, milking, feeding and other dairy management programs. Contact your local Cooperative Extension Office for assistance.
- Thoroughly test the milking system and its components to ensure that they are operating correctly.
- Have an electrician completely check the farm’s electrical system for N-E voltage. If excessive neutral-to-earth voltage is detected, repair or modify the electrical system to reduce it to a tolerable level.
- If an off-farm N-E voltage source is the significant cause, contact your power supplier.
For more information on neutral-to-earth voltage, contact your county Cooperative Extension Office. Videotapes related to N-E voltage are also available by writing to:
The National Food and Energy Council
409 Vandiver West, Bldg. 4, Suite 202
Columbia, MO 65202
Or by calling: (314) 875-7155.