Authors: Christopher D. Wyckoff and Glen H. Hetzel, Biological Systems Engineering Department Virginia Tech
October, 1996
Table of Contents
Introduction
What to Do In Case of An Accident
Electricity, or electric current, is the flow
of electrons from one atom to another in
any material. Materials that allow
electricity to flow easily are called
conductors. Most metals, such as copper
and aluminum, make good conductors of
electricity. Insulators are materials that do
not allow electricity to flow through them.
Good examples of insulators are glass,
plastic, and rubber. Unfortunately, our
bodies can allow current to pass through
them, causing anywhere from a mild
tingling sensation to cardiac arrest and
burning.
There are many ways in which electrical accidents happen.
Hazards result from the
degradation of electrical wire insulation due to rodents,
weathering, or normal wear, improper
wiring, improper wire size or type, and corrosion of
electrical connections, for example. In addition
to these normal hazards, agricultural workers are
particularly subject to the hazards of electricity
because tall equipment, such as grain augers, combines, and
raised dump truck beds can become
entangled in overhead power lines. Accidents have also
occurred with overhead power lines when
moving irrigation pipe. Agricultural buildings are subject
to dusty, moist and corrosive
environments, making them especially troublesome when using
electricity. Electricity was the
seventh largest cause of deaths on farms in 1988, and causes
unknown amounts of property and
livestock loss every year. Fortunately, there are several
devices and methods that can be employed to
protect yourself, your animals, and your property.
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Fuses and circuit breakers have a numbered rating system
which indicates the maximum
amount of current that they will allow through. The fuses
and circuit breakers are matched to the size
of the electrical wires used in the system. Thus, fuses
should always be replaced with a new fuse of
the same rating. A higher rated fuse will not offer any
protection if the system was to draw too much
electricity and could result in an electrical fire or damage
to your equipment. A smaller rated fuse will
cause the circuit to blow the fuse more frequently, leading
to your aggravation and the temptation to
bypass the system. If absolutely necessary, use a smaller
rated fuse for temporary power, but never
a larger one.
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Never destroy or cut off the round grounding
prong on a plug to fit it into a socket or extension cord
that
does not accommodate the prong. If the equipment you are
working with does not have a ground wire, then consider
rewiring the device to accommodate the grounding feature.
Another option is to use double insulated tools. These tools
have an air space around the device to help insulate you
from an electrical shock.
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There are three different types of GFCI's
available. The most common type is the GFCI
breaker. These are used instead of conventional
breakers to protect everything on the circuit.
There are also GFCI outlets that can easily
replace conventional outlets. These will offer
protection for everything plugged into them.
There are also portable types that can be plugged
into any outlet. The device you want to use is
then plugged into theGFCI. All GFCI's are equipped with test
buttons which intentionally cause a ground fault to insure
the device is working properly. It is recommended that all
GFCI's be tested every month.
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Even with all of these protective devices in place, you
can still get shocked if you accidentally touch both the hot
and
neutral wires of a live circuit. This is different from a
ground
fault because during a ground fault only some of the current
in
the circuit will flow through you to ground. If you touch
both
hot and neutral wires then all of the current in the system
will
flow through you and your body will act as a normal
electrical
device. Therefore, there are additional precautions you need
to
take to prevent accidental death
and injury.
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2. Treat every electrical wire as a"hot" wire.
3. Check the condition of all power cords and devices and
repair or replace as necessary.
4. Make sure power is disconnected before working on any
electrical device.
5. If a "hot" circuit must be worked on, call a qualified
electrician.
6. Use double insulated tools, which put an additional
barrier between you and electricity.
7. Make sure that any wiring you do meets the suggestions
from the National Electric Code,
which are contained in most books on electricity.
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Another special problem with electricity on the farm is
the dusty, moist and corrosive
environments of most livestock houses. There are waterproof,
dustproof, and even explosion proof
electrical boxes, outlets, and motors available for use in
the uniquely troublesome environments of
livestock facilities. These materials ensure safe and
reliable use of electricity throughout your farm.
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Introduction
What Can You Do?
There are four kinds of electrical safety devices and
features that you should be aware of.
These are fuses and circuit breakers, GFCI's, grounding, and
polarization.
Fuses and Circuit
Breakers
The most common form of electrical
protection is the fuse or circuit breaker. These are
devices that are designed to protect the electrical
system from too much current. These devices,
when used properly, work well to protect
equipment and prevent electrical fires due to
overloads on the electrical system. They do not,
however, protect an individual from electrical
shock. Fifteen amps, which is typically the
smallest size breaker found in a normal
household, is 250 times greater than is required to cause
cardiac arrest in an individual.
Grounding
Another important safety feature is "grounding."
Grounding occurs when a ground wire is
connected from ground potential to the frame of an
electrical device. Grounding is not necessary for a
circuit to work, it is only there for the protection of
individuals from stray current. In a normal
circuit, electricity flows from the "hot" wire (which is
usually black) to the electrical device and back
to ground potential through the neutral wire (which is
usually white or gray). A ground wire (which
is usually bare or green) is provided so there can be an
alternate path for the electricity to flow back to
ground potential if an electrical short occurs. For example,
if the wires inside an electrical device have
become worn or the insulation broken down such that the hot
wire makes contact with the case on the
device, then the current could possibly flow through the
individual using the device back to ground.
If a ground wire is present, however, the current will take
the path of least resistance and flow
through the ground wire back to ground instead of flowing
through the individual causing an
electrical shock.
GFCI's
Another protective device that can be used is called a
Ground Fault Circuit Interrupter,
commonly referred to as a GFI or GFCI. This device is meant
to protect human beings from electrical
shocks due to faulty electrical equipment. A GFCI works by
monitoring the current flow to an
electrical device and comparing it to the amount of current
flowing back. If there is a difference
between these two values, this means that some electricity
is flowing back to ground through a path
other than the wire. This is called a "ground fault" and
when the GFCI detects this, it stops current
flow altogether in the circuit. Consider the previous
example in which the wires inside an electrical
device have become worn or damaged so that the hot wire
makes contact with the casing. If a person
were to use the tool, then electricity could possibly flow
through the individual back to ground.
When a GFCI detects this situation, it stops current flow
before harmful amounts of electricity flow
through the individual. Electricity will flow through an
individual easier if the person is working in
wet or damp conditions, which is why it is recommended that
GFCI's be installed in all bathrooms,
kitchens laundry rooms, garages, and other buildings where
moisture can be a problem. The
protection from grounding and from a GFCI are similar.
However, if your equipment does not have
a ground wire, then a GFCI is your only form of protection
from faulty equipment. GFCI's also
offer protection if the grounding mechanisms are faulty.
Polarization
Polarization refers to the plugs and outlets that have
two different sized prongs or slots. The
idea behind polarization is to ensure that the hot wire
travels through the switch on the device before
it encounters the load or resistance. This helps ensure
there are no "live" wires that are exposed
unless the switch is turned on and current is traveling
through the entire circuit. Consider, for
example, a lamp; without polarization, the hot wire could be
traveling through the socket and then to
the switch. If someone was to then touch the socket, they
could be shocked. Polarization ensures that
the hot wire travels through the switch first, protecting
you from accidental contact with an energized
socket.
What Else Can You Do?
1. Install and use the electrical safety devices that are
available.
Sizing Electrical
Wires
The size of wire chosen, usually expressed in the
American Wire Gauge number, for
electrical circuits is determined by the electrical load.
The larger the wire size number, the smaller the
wire and therefore, the smaller the electrical load that can
be operated through that circuit. The
distance the electricity has to travel also makes a
difference. You can not simply take a 12 gauge 100
ft. extension cord and expect to run a 1 hp motor
efficiently. Improper wiring can result in decreased
efficiency and heat build up in the wire, which in turn can
result in a fire. Proper wiring is
accomplished by looking at charts, which will yield you the proper
gauge wire for a given load and a given distance for a 120
Volt AC circuit. Charts can be found in most books on electricity.
What About the Special Risks to
Farmers?
Entanglement with overhead power lines is a special
problem on farms. There are several things you can do to
protect
yourself from entanglement with overhead power lines. The
best
option is to bury all electrical wires underground. This
will
eliminate the possibility of entanglement, but caution will
be
needed when digging. Always check with your electric company
or call "Miss Utility" before digging to determine if there
are any
underground utility lines in the area. Another thing you can
do is
to ensure that all augers, dump truck beds, etc., are
lowered
before moving them. This simple procedure will prevent most
accidental entanglements. Another thing you need to be
careful of
is bumping into the guide wires on electrical poles. This
will
cause sagging in the overhead lines and will make
entanglement
more likely. Always stay alert and never take unnecessary
risks.
What to do in Case of an Accident
So far we have focused on ways to prevent electrical
accidents and misuse. If an accident still
occurs, then certain steps should be taken.