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motors II

lesson 3 Motor Protection

QuestionAnswer
A(n) ? in a motor is caused by a load that exceeds the full-load rating of the motor. overload
true/false Fuses and circuit breakers (CBs) are used for ground-fault and short-circuit protection; overload relays are typically used for overload protection. true
true/false The NEC® requires overcurrent protection of motor installations. true
A(n) ? condition causes the current to rise hundreds of times higher than normal at a very fast rate. short-circuit
true/false A ground fault is an unintentional connection between an ungrounded conductor and any grounded raceway, box, enclosure, or fitting. true
An OCPD must be used to provide protection from short circuits and ? . ground faults
The function of an OCPD is to protect branch circuit conductors, control equipment, and motors from damage caused by a(n) ? . overcurrent
A type S fuse is a ? type fuse. plug
true/false Fuses themselves do not need to be maintained. The fuse holders, terminations, and disconnects should be inspected regularly. true
Cartridge fuses are available with amperage ratings from 0 amperes to ? . 6000A
true/false To avoid nuisance tripping due to equipment startup characteristics, time-delay fuses do not allow overcurrents to exist. false Time-delay fuses allow overload currents to exist for short periods to avoid nuisance tripping due to equipment start-up characteristics.
? fuses are also known as dual-element fuses. Time-delay
true/false CBs offer the benefit of not damaging themselves but are not resettable after an overload has cleared. false they are resettable
A(n) ? circuit breaker uses a bimetal strip connected in series with the load to open a circuit. thermal-magnetic
true/false In thermal-magnetic CBs, the thermal element provides faster protection for ground faults and short circuits while the magnetic element is used for overload protection. false the thermal element is used for overload protection while the magnetic element provides faster protection for ground faults and short circuits.
true/false Both magnetic and thermal-magnetic circuit breakers use a spring-loaded electrical contact that opens the circuit. true
A(n) ? circuit breaker operates immediately and has no delay between the sensing element and the tripping action of the device. instantaneous-trip
The ? rating of an OCPD is the maximum amount of current that can be safely applied while still maintaining the physical integrity. interrupting
true/false The melting point of a eutectic alloy never changes and is not affected by repeated melting and resetting. true
true/false A heater coil converts the excess current into heat. When enough heat has been generated, it melts the eutectic alloy. The eutectic alloy is used with a mechanical mechanism to activate a tripping device when an overload occurs. true
true/false Under any load condition, the motor draws only the amount of current required to keep the shaft rotating at the rated revolutions per minute. true
A ? overload relay uses a resistive heating element to open a set of contacts. thermal
A(n) ? indicates the maximum length of time it takes for the overload relay to trip at 600% overload. overload class rating
Created by: Yusosweet1
 

 



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