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Overcurrent Protection NEC Article 240 and Beyond (Hardcover)
Loot Price: R2,933
Discovery Miles 29 330
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Overcurrent Protection NEC Article 240 and Beyond (Hardcover)
Expected to ship within 9 - 15 working days
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An overcurrent is caused by a short-circuit, ground-fault, or an
overload. A short-circuit may be hundreds or even thousands of
times above the normal operating current. This type of fault may be
an arcing fault between ungrounded conductors or between an
ungrounded conductor and a grounded (usually, a neutral) conductor,
a line-to-line arcing fault may produce a current of 74% of a
3-phase bolted fault. A line-to-neutral arcing fault will be
somewhat less. A line-to-line bolted fault, the equivalent, of the
conductors bolted together, may be up to 100% of the available
short-circuit current. A line-to-neutral bolted fault may be in
excess of 100% of the 3-phase bolted fault at the source, but
considerably less downstream. A ground-fault, that is, the
equivalent of a connection between an ungrounded conductor and the
equipment grounding system, will produce a current that may be 38%
or higher of the 3-phase bolted fault current. These types of
faults are typically arcing faults which normally are intermittent
in nature. That is, they strike and restrike over time and may
produce a short-circuit fault due to insulation damage. Once again,
a line-to-equipment ground fault near the source may produce a
fault current of over 100% of the 3-phase bolted fault, but
considerably less downstream. An overload typically ranges from one
to six times the normal current, and are normally caused by motor
starting currents or transformer magnetizing currents. These
conditions are of such short duration that the circuit components
are not damaged. This book has a detailed analysis of these types
of faults, along with explanations and examples of the various
types of overcurrent protective devices to assure proper
protection. This volume has extensive information on the
application of overcurrent protection for conductors and equipment.
The reader will be able to calculate fault currents as well as
establishing the short-circuit withstand rating of conductor
insulation and to determine the appropriate type of overcurrent
devices based on circuit conditions. In addition, determining
ground-fault currents for the purpose of selecting the proper size
of equipment grounding conductors to establish an effective
ground-fault current path is discussed in detail. Readership -
Anyone involved with the design of overcurrent protection for
electrical distribution systems from the system source to the
electrical utilization equipment. The emphasis is placed on the
design of the overcurrent protection for specific installations to
assure proper protection for the circuit components regardless of
the type of fault encountered.
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