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Circuit Protection Devices
A.
Bhatia
Overview
Too much current flowing
through an electric circuit can damage the circuit and create a safety hazard.
How much current is "too much current"? That depends on the circuit and its
components. For some circuits, 1 ampere would be too much current, while for
other circuits 1 ampere would be perfectly acceptable.
Circuit protection devices
protect electrical equipment by rapidly disconnecting power to components in the
event of abnormal overload conditions resulting from excessive voltages, ground
faults, and accidental shorting of a circuit.
Two types of circuit
protection devices are common; fuses and circuit breakers both operate by
opening and interrupting current to the circuit. A fuse or circuit breaker is
designed to create an open circuit if too much current flows through it. You can
think of it as a switch that automatically turns itself off if the current
through it exceeds a certain level. When a fuse is "blown" by having too much
current pass through it, the fuse is ruined and must be replaced. On the other
hand, when a circuit breaker is "tripped" by excessive current, the circuit
breaker can be reset and used again, instead of being discarded. The choice of
which to use depends on the specific application, circuit type, its electrical
specifications, space available, environmental constraints, and customer
preference. In the
US, the National Electric Code (NEC) exists to guide electricians in the proper
installation of electrical equipment and defines the specific requirements for
circuit protection. In Canada the Canadian Electric Code (CEC) exists to provide
similar guidance. Other areas of the world have equivalent country or local
codes.
A proper
circuit protection strategy reduces long-term maintenance needs and other costs,
and minimizes system downtime.
This 3-hr course provides
an overview of circuit protection devices and is based entirely on Naval
Education and Training Materials (NAVEDTRA
14175),
Electricity and Electronic Training Series;
Module-3 and covers
Chapter 2 titled “Circuit Protection Devices”.
The student must take a multiple-choice quiz consisting of
fifteen (15) questions at the end of
this course to obtain PDH credits.
Specific Knowledge or Skill Attained
This course teaches the following specific knowledge and
skills:
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The reasons why
circuit protection is needed
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Definitions of a
"direct short", "excessive current condition" and "excessive heat condition"
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How circuit
protection devices are connected in a circuit
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Circuit protection
devices - types and characteristics
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The three time delay
ratings of circuit breakers
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Selective tripping
and why it is used
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The factors used in
selecting circuit breakers
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The methods of
checking and the items to check when replacing/maintaining fuses and circuit
breakers
Course
Click on the following PDF attachment and review the document prior to taking
a quiz for credit.
Circuit Protection Devices (497 KB)
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To obtain PDH credits for this course, you will need to take a quiz for
credit. Click on the link below.
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