Review Master Electrician (Part 2) Questions and Answers 100% Correct!

The ordinary direct current series motor does not operate satisfactorily with alternating current. One of the main reasons for this is a. excessive heating due to eddy currents in the solid parts of the field structure b. that the armature current and field current are out of phase with each other c. that the field flux lags 120 in time phase with respect to the line voltage d. excessive heating due to the low voltage drop in the series field - ANSWER-a. excessive heating due to eddy currents in the solid parts of the field structure A DC elevator motor, on a gearless traction machine, has a series field for compounding during the acceleration period. This field is cut out when the motor has reached full speed, for the purpose of a. preventing excessive heat b. reducing the line current c. providing constant speed over a wide range of load conditions d. saving the cost of losses in the series field - ANSWER-c. providing constant speed over a wide range of load conditions The protective device for a motor branch circuit a. should have a rating equal to or greater than the starting current of the motor b. should have a rating equal to the full load current of the motor c. should not be of the instantaneous type d. should have a rating equal to the current capacity of the circuit conductors - ANSWER-c. should not be of the instantaneous type When both fuses and thermal cutouts are used in a motor circuit, the a. ratings of the fuses should be the same as those of the thermal cuts b. fuses are used to protect against continuous, but not large overloads c. thermal cutouts are used to protect against continuous overloading d. thermal cutouts are used to protect against short-circuits in the motor and branch circuit - ANSWER-c. thermal cutouts are used to protect against continuous overloading To temporarily change the direction of rotation of a single-phase, shaded-pole, induction motor you would a. do nothing since it cannot be done b. reverse the connections to the starting winding c. shift the brushes to the opposite neutral d. reverse the line leads - ANSWER-a. do nothing since it cannot be done For maximum safety the magnetic contactors used for reversing the direction of rotation of a motor should be a. electrically interlocked b. electrically and mechanically interlocked c. mechanically interlocked d. operated from independent sources - ANSWER-b. electrically and mechanically interlocked Silver electrical contactors are tarnished most readily by a. oxygen b. hydrogen c. nitrogen d. sulphur - ANSWER-c. nitrogen The lubricant used for sleeve bearings on motors is usually