Chat with AIExam 23: Troubleshooting, Motor Installation and Developing Control Circuits
When using an ohmmeter, make certain that the ____.
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VerifiedD
How do you determine locked rotor current?
(45) VerifiedThere are two basic methods for determining the locked rotor current (starting current) of a squirrel-cage induction motor, depending on the information available.
If the motor nameplate lists code letters that range from A to V, they indicate the type of rotor bars used when the rotor was made. Different types of bars are used to make motors with different operating characteristics. The type of rotor bars largely determines the maximum starting current of the motor. NEC Table 430.7(B) lists the different code letters and gives the locked-rotor kilovolt-amperes per horsepower. The starting current can be determined by multiplying the kilovolt-ampere rating by the horsepower rating and then dividing by the applied voltage.
The second method of determining locked rotor current is to use Tables 430.251(A) and (B) if the motor nameplate lists NEMA design codes. Table 430.251(A) lists the locked rotor currents for single-phase motors and Table 430.251(B) lists the locked rotor currents for poly-phase motors.
Speed control for a wound rotor motor is obtained by placing ____________________ in the secondary or rotor circuit.
(39) Verifiedresistance
Which of the following can turn a pump motor off if the temperature of the heat exchanger should become excessive?
(40) Troubleshooting is a matter of progressing logically through a circuit.
(42) The three main instruments used by an electrician to troubleshoot a circuit are the voltmeter, ohmmeter, and ____________________.
(42) If an air induction blower fails for some reason other than the overload contact opening, the high-pressure pump motor will continue to inject oil into the combustion chamber. To prevent this situation, a(n) ____________________ switch can be added to the circuit.
(40) If pump 1 is to operate alternately with pump 2, some method must be devised to remember which pump operated last. This function is performed by a(n) ____.
(36) A control transformer cannot be used to change incoming voltage from 240 volts to 120 volts.
(35) What are some requirements for a wound rotor induction motor speed control circuit?
(45) Starter sizes are rated by motor type, ____, and connected voltage.
(31) The full-load efficiency indicates the overall efficiency of the motor.
(35) The motor overload size is to be determined by the nameplate rating of the motor.
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