Electrical shocks and burns are common hazards
to personal who are employed in the heating and air-condition industry. It is
impossible to install or troubleshoot air-conditioning equipment without
working close to electrical devices that are being supplied with electrical
energy. It is the responsibility of the technician to develop a procedure for
working around live electric circuits without coming in contact with conductors
and electrical components that are being supplied with electric power.
Electric shock occurs when a person becomes
part of an electrical circuit. When electricity passes through the human body,
the results can range from death to a slight, uncomfortable stinging sensation,
depending upon the amount of electricity that passes through the body, the path
that the electricity takes, and the amount of time that the electricity flows.
Technicians should never allow themselves to become the conductor between two
wires or a hot and a ground in an electric circuit.
The amount of electrical energy needed to cause
serious injury is very small. The electrical energy supplied to an electrical
circuit is called electromotive force (emf), and it is measured in volts. In
the heating and air-conditioning industry, the technician often is in close
proximity to 24 volts, which is used for the control circuits of most
residential systems; 120 volts, which is used to operate most fan motors in gas
furnaces; 240 volts, which is used to operate compressor in residential
condensing units; and much higher voltages, which are used to operate
compressor in commercial and industrial cooling systems. The heating and air-conditioning
technician is often around voltages that can cause serious injury or even
death.
Your body can become a part of an electrical
circuit in many ways. First, your body can become part of an electrical circuit
if you come in contact with both a conductor that is being supplied with power
and the neutral conductor or ground at the same time, as shown in Figure 1. The
ground in an electrical system is a conductor primary used to protect against
faults in the electrical system and does not normally carry current.
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| Fig 1 |
The neutral is a current-carrying conductor in
normal operation and is connected to the ground. Another way that you can
become part of an electrical circuit is to come in contact with both a
conductor supplied with power and with the ground, as shown in Figure 2. A conductor
is a wire or other device that is used as a path for electrical energy to flow.
You may become a part of the electrical circuit if you touch two conductors
supplied with electrical energy, as shown in Figure 3.
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| Fig. 2 |
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| Fig. 3 |
The severity of injury from electric shock is
directly related to the path that current flow takes in the body. The current
flow is the amount of electrons flowing in a circuit and is measured in
amperes. For example, if the thumb and index finger of the same hand in contact
with a conductor that is supplied with electrical energy and a neutral as shown
in Figure 4., then the path would only be from the thumb to the index finger. If
you touch a conductor being supplied with electrical energy with the other
hand, then the electrical path would be from one hand up the arm and across the
heart to the other arm and to the hand, as shown in Figure 5. If the path is
through an arm and a leg, then it would also across or come near to the heart. When
the path of electrical flow across the heart, the risk of serious injury
increases. Most fatal electrical accidents happen when the electrical flow
passes near or through the heart. When the electrical path crosses near or
through the heart for only a short period of time, it can cause ventricular
fibrillation of the heart, in which the heart only flutters instead of beats
and the blood flow to the body stops. Unless the heart beat is returned to normal
quickly with immediate medical attention, the person will usually die.
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| Fig. 4 |
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| Fig. 5 |
The other injury caused by electrical shock is
burns to the body. This usually occurs when the technician is shocked with high
voltage. Electrical burns can come from an electrical arc, such as the arc from
a high-voltage transformer, he arcing of high voltage, and a short circuit to
ground, where electrons are allowed to flow unrestricted. For example, if you
are working in an electrical panel with a screw driver and allow the blade of
the screwdriver to touch aground while in contact with a conductor that is
being supplied with electrical energy, the potential difference is tremendous,
and sparking will usually occurs, as shown in Figure 6. If the resistance is
very small, then the current flow in the circuit will be very large.
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| Fig. 6. |
A current flow through the body of 0.015 ampere
or less can prove fatal. By comparison, the current draw of a 60-watt light
bulb is only 0.50 ampere.
The following values can be associated with the feel of electrical shock;(1) 0.001 ampere (1 milliampere), a person can feel the sensation; (2) 0.020 ampere (20 milliamperes), a person might not be able to let go; (3) 0.100 ampere (20 milliamperes) can cause ventricular fibrillation; and (4) 0.0200 ampere and above (˃200 milliamperes) can cause severe burns and respiratory paralysis.
Another danger of electrical shock is a person's
reaction when shocked. For example, if you are working on a ladder and get
shocked, you could fall off the ladder. If you are using an electrically
powered hand tool and a short occurs, then you might drop the tool, causing
personal injury to yourself or others. Technicians should keep in mind that
their reaction when getting shocked could endanger others, so they must be
cautious and attentive when working near live electrical circuits.
Technicians should be aware of the danger of
electrical shock when using ladders that conduct electricity, such as aluminum
ladders. If at all possible, the Technician should use nonconductive ladders on
all jobs. The two primary types of nonconductive ladders used today are wood
and fiberglass. Non conductive ladders work as well as the aluminum ladders
except that they lack the same ease of handling because of their added weight. Whenever
you are using a ladder, you should make sure that you do not position the
ladder under electrical conductors that you might accidentally come in contact
with when climbing the ladder.
Mind that their reactions when getting shocked
could endanger others, so they must be cautious and attentive when working near
live electrical circuits.
Technicians should be aware of the danger of
electrical shock when using ladders that conduct electricity, such as aluminum
ladders. If at all possible, the Technician should use nonconductive ladders on
all jobs. The two primary types of nonconductive ladders used today are wood and
fiberglass. Nonconductive ladders work as well as the aluminium ladders, except
that they lack the same ease of handling because of their added weight. Whenever
you are using a ladder, you should make sure that you do not position the
ladder under electrical conductors that you might accidentally come in contact
with when climbing the ladder.