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Frequently Asked Questions - Stray Voltage
If the following questions do not hit on what you need to know, please
contact us. If you prefer,
you can also schedule a visit from your
agricultural consultant.
Stray Voltage Regulations and Testing Procedures
- How many phone calls does Public Service receive concerning stray voltage?
- The number of calls we get varies by the areas we serve and the time of year.
On average, we receive about 20 calls a month.
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- When a farm customer calls about stray voltage, what steps does
Public Service take?
- During the call, we try to determine whether the customer
simply wants to know the level of stray voltage on the farm, or if
there are actual problems occurring. We try to schedule a visit
to the farm within a few days. We then assess the farm's whole
electric system and cow contact voltages using the proper equipment.
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- What does Public Service consider as the level of concern
for stray voltage?
- Public Service abides by the Public Service Commission of Wisconsin's
(PSCW) level of concern: 2mA of steady state current flowing in a cow contact
area (Docket 05-EI-115). The level of concern is the point at which action
should be taken to reduce cow contact currents.
If a stray voltage investigation reveals that there is more than 1 mA
between cow contact points, we are required to determine the amount of influence
Public Service has on that farm. If we are responsible for more than 1 mA of
stray voltage, we will take action to reduce it below that level. Research shows
that only a very small percentage of cows detect 2 mA of stray voltage.
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- How often does Public Service determine that the level of
stray voltage is above the level of concern?
- Less than 10 percent of the time.
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- If Public Service finds that stray voltage levels are below
1 mA, then what?
- During our investigations, we often find improper electrical
wiring that is not causing stray voltage, but may be a safety hazard
or a code violation. If necessary Public Service can help the
customer get in contact with an electrician to correct these problems.
It's difficult to pinpoint any one cause of reduced milk production
or animal stress- there are so many factors involved in farm management
and production. Our area of expertise is electrical concerns, so we try to
contain our assistance to that area. And if we have exhausted the possible
electrical causes for customer's problems, we recommend seeking the
advice of a feed consultant, veterinarian, milk equipment dealer or other
expert. We want to help solve our customers' problems, whether it's stray
voltage or not.
Another resource for customers is Rural Electrical Power
Services (REPS). REPS will provide technical advise to farmers regarding
stray voltage and power quality issues and also work with farmers to resolve
herd health and production problems.
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- What can farmers do if they are not satisfied with the
Public Service investigation?
- Farmers can contact the REPS team. The REPS team reviews our
findings, conducts its own farm investigation and may ask Public
Service to do further work. They might ask us to make changes or
validate what we have found. In general, they just make sure that
all bases have been covered and do their own analysis of the data.
If the REPS team finds that the utility should make some corrections,
the Public Service Commission of Wisconsin has the authority to order
compliance.
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- Public Service incurs some cost when it needs to fix a
stray voltage problem. Is that ever a factor when Public
Service determines whether or not a problem exists?
- If there is a utility problem, we fix it.
Period.
We have a strong commitment to our customers. We talk to
them about electrical safety, wiring codes and how they can
save money by conserving energy. We improve our electric
distribution system continually and have one of the best
distribution systems in the state.
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Understanding and Preventing Stray Voltage
- What is the difference between a volt and a milliamp?
- Volts and milliamps are measurements of electricity. In
case of stray voltage, the number of volts describes the potential
(or push) for current to flow through the cow, and the number of milliamps
is a measurement of this current. Since a cow has a resistance of about
500 ohms, one volt applied across the cow, from hoof to mouth, will cause
two milliamps of current to flow through the cow; two volts applied
across the cow will cause four milliamps of current to flow through
the cow.
This follows Ohm's Law: Voltage = Current (amps) X Resistance (ohms)
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- Do equipment planes reduce stray voltage?
- If installed properly, an equipotential plane can reduce levels of
stray voltage by keeping all surfaces that livestock touch at approximately
the same electrical potential. This is done by installing a wire mesh in
the floor and bonding it to the stall, water system and grounding system.
Installation of an equipotential plane is highly recommended, especially when
new stall barns, freestall barns and parlors are being planned.
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- Is stray voltage reduced by moving the transformer out of the yard?
- There is no reason to move the transformer away from livestock housing facilities.
In fact, distancing the transformer can actually increase the levels of stray
voltage if the customer's neutral conductor is not properly sized. When the
transformer is moved away from the barn, the neutral wire is lengthened and the
voltage drop on the neutral wire is increased. This voltage can show up in the cow
contact area, so it is important to keep the transformer located close to the housing
facilities.
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- Do rubber mats prevent stray voltage?
- No, not really. In most cases, rubber mats are made from recycled tires.
These mats are porous and some may contain metal fragments. In addition,
accumulated manure and urine can negate any insulating value the mat may add.
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- Does it make sense to install a piece of plastic in the water line to reduce stray voltage?
- No. Installing plastic in the water line can actually cause a dangerous situation. If
a piece of equipment faults or shorts out , the fault current is better able to flow back to
the source when the water line is continuous metal. This flow of fault current will trip a
circuit breaker and turn off the failing equipment. A piece of plastic inserted in the water
line could actually prevent the circuit breaker from tripping and create a dangerous situation
in which a person or animal could be electrocuted.
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- What is a neutral isolator and why is it used?
- A neutral isolator is a device that is installed between the utility (primary)
neutral conductor and the farm (secondary) neutral conductor, separating the two.
Although a neutral isolator will reduce the effect of primary neutral voltage on the
farm, it will not prevent an on-farm electrical problem from affecting the cattle.
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- How much does a neutral isolator cost?
- Public Service customers can have a neutral isolator installed on their farm
for an initial cost of $950, plus $35 tax per month. The monthly charge pays for
maintenance, annual inspection and testing by Public Service. Farm wiring must meet
the National Electric Code before we will install the isolator. If the neutral
isolator is removed before the end of the 12th month, the monthly payments will be
refunded.
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- What is the difference between a neutral isolator and an isolation transformer?
- An isolation transformer accomplishes the same thing as a neutral isolator. This
is done by separating the windings of a transformer. This option usually costs more
than a neutral isolator because of the cost of the equipment installed. Also, the
isolation transformer belongs to the farmer, who is responsible for maintenance in
the event of lightning damage or transformer failure.
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