1C.7.1—Stray Voltage(PacifiCorp Engineering Handbook)

1C.7.1—Stray Voltage

1 Scope

This document provides basic information on stray voltage and some of its common causes.
Stray voltage can affect livestock and voltage-sensitive equipment (VSE) such as computers. Although
the measurement and mitigation techniques presented are applicable for problems with
VSE, this document does not thoroughly cover these applications; instead it focuses on livestock.
For computer problems due to stray or neutral to ground voltages, see IEEE 1100 for recommended
grounding practices or mitigation techniques. The other references are also excellent
for those desiring a more thorough treatment of stray voltage and its effects.

2 References and Resource Documents

The references and resource documents listed below apply to the extent specified in the body of
this standard. Wisconsin Power Company, Stray Voltage Detection IEEE 1100–1992, Emerald Book. I

EEE Recommended Practice for Powering and Grounding Sensitive Electronic Equipment

(Source for information on stray voltage and its effects on electronic equipment.)
Wisconsin Power Company, Equipotential Planes for Stray Voltage Reduction
United States Department of Agriculture, Handbook 696, Effects of Electrical Voltage/Current
on Farm Animals, How to Detect and Remedy Problems, commonly called the “Cow Book.”

3 Definition of Stray Voltage

Stray voltage is a small voltage that can exist between two surfaces, which an animal can touch
simultaneously. Stray voltage is a special case of neutral-to-earth voltage (NEV); it differs from
NEV because it is defined at a specific location.

NEV is a normal result of operating any grounded electrical system; this includes the customer’s
electrical system as well as PacifiCorp’s system. NEV is a voltage between the neutral conductor
and the earth when measured to an electrically remote ground reference point. NEV is the result
of current flow through the resistance of the grounded neutral conductors and connections. The
current that flows may be either normal return current or electrical fault current.

Low levels of ac voltage on the grounded conductors of a farm wiring system are a normal and
unavoidable consequence of operating electrical farm equipment. Stray voltage is the general
term used to describe these low-level voltages when they are measured between two objects that
can be contacted simultaneously.

4 Possible Sources of Stray Voltage

Stray voltage on a farm is, typically, the result of several voltage sources acting simultaneously.
Both on-farm and off-farm sources may contribute to the level of stray voltage present. Some of
the common on-farm sources of stray voltage are:
1. Interconnection of equipment grounding conductors and neutral circuit conductors at
places other than required by the National Electrical Code
2. Inadequate connections on the neutral or ground wire system (such as corroded connectors,
or broken grounding wires)
3. Poor grounding conditions (such as high soil resistance, or loose ground connections)
4. Undersized neutral conductors
5. Dirty, dusty, corroded, cobwebbed or damaged electrical boxes and devices
6. Unbalanced 120 volt loads
7. Defective electrical equipment (such as insulation break down in a motor)
8. Normal operation of electrical equipment in distant parts of the barn or in remote areas
(may result in stray voltage within animal confinement areas)
9. Defective underground cable
10. Electrical load with high harmonic currents

 

 

Figure 1 – Typical Farm Electrical System

An improperly grounded neutral at a sub panel is shown in Figure 1 as an example of how stray
voltage can come from an on-farm source. The improperly grounded neutral conductor can be the
source of earth currents via the ground wire and its multiple ground connections. This earth current
will result in voltages seen between grounded objects; this is stray voltage.

5 Effects of Stray Voltage

Symptoms reportedly attributed to significant levels of stray voltage include:
1. Decreased milk output of dairy cows
2. Animals’ reluctance to eat or drink from a feeder
3. Improper operation of sensitive electronic loads

6 Levels of Voltages Encountered

It is important to make a distinction between low-level stray voltage and the more hazardous
voltages that produce a painful shock.

6.1 Personal Shock
When you experience a painful personal shock, you are not feeling stray voltage. Personal
shock usually indicates defective phase or “hot leg” wiring or equipment. Since these
conditions may be hazardous, call an electrician.

6.2 Tingle Shock
If you are feeling a low-voltage “tingling” when in the barn, this could be an indication of
an electrical device with an internal short, particularly if it disappears when the device is
unplugged. If this happens you should call an electrician to fix the device.

6.3 Symptoms Present but No Tingle Shock Can Be Felt
Livestock may feel voltages not sensed by humans because the animal’s body resistance is
less than that of a human. Voltage measurements should be taken wherever livestock exhibit
symptoms attributed to stray voltage. If you are unsure of how to take voltage measurements,
you should consult an electrician or PacifiCorp. Typically, stray voltage measurements
are made with a digital voltmeter with a 500 ohm shunt resistor. The 500 ohm resistor
approximates the body resistance of a full grown cow. Measurements can be made using
the point-to-point method; that is, measuring the voltage between any two points that an
animal may contact with a digital voltmeter and a 500 ohm shunt resistor.

 

 

Figure 2 – Digital Voltmeter with 500 ohm Two Watt Flame-proof Shunt Resistor

 

NOTE:

THE SHUNT RESISTOR MUST BE REMOVED FROM THE METER BEFORE USING THE
METER TO MEASURE ENERGIZED CONDUCTORS. REFER TO USDA HANDBOOK 696
FOR DETAILS on VOLTAGE MEASUREMENT.

7 Interpreting Voltage Data

Research indicates that corrective action is not needed for voltages below 1.0 volt when using a
500 ohm shunt resistor to measure stray voltage. Usually voltages will be measured between
points that the animals can touch simultaneously.

CAUTION

For your own safety, do not attempt to make electrical measurements on electrical wiring or within
electrical boxes or cabinets unless qualified to do so. Do not use the voltmeter with the shunt
resistor to measure voltage on any energized parts.

 

 

Figure 3 – Measuring Stray Voltage Using a Digital Voltmeter with a 500 ohm 2 watt
Flame-proof Shunt Resistor

 

NOTE:
THE VOLTAGES MEASURED ARE AT POINTS THAT CAN BE CONTACTED SIMULTANEOUSLY.

8 Reducing Levels of Stray Voltage

Most of the sources of stray voltage are in the facility. Some of the methods used to reduce the
level of stray voltage may require the use of an electrician and are listed below.
1. Confirm that the wiring meets the current National Electrical Code.
2. Bond all metal objects that animals can touch simultaneously.
3. Balance 120 volt loads, use 240 volt equipment when possible.
4. Replace bolted connections with compression connections.
5. Oversize neutral wires.
6. Use of 240 volt equipment to reduce neutral current.
7. Increase size of and decrease length of the secondary conductors.
8. Install an equipotential plane.

 

9 Issuing Department

The Standards Services department of PacifiCorp Engineering is responsible for issuing this
document. Comments and suggestions are welcome. Additional copies may be obtained from:
Address: 201 South Main, Suite 2000
Salt Lake City, Utah 84140-0020
telephone: (801) 220-2034
fax: (801) 220-2258

10 Approvals and Authorization

The persons listed below approved this document. Their signed management approval records
are on file in Standards Services. Publication and use of this document is authorized by the
director of Standards and Technical Support. The signature of the manager of Standards Services
below indicates that all required approvals and authorization have been received.

 

C. Paul Dalpiaz, director
Standards and Technical Support
Darrell T. Gerrard, director
Transmission and Distribution Engineering
Blaine Stewart, assistant vice president
Customer Operations
Approvals and authorization received:

Merrill L. Brimhall, manager
Standards Services