Motors
100: A motor uses opposing electromagnetic fields in order to rotate the motor shaft. What creates the stationary electromagnetic field?
a) Stator
b) Rotor
c) Winding A
d) None of these
a) Stator
100: A generator produces electrical energy by converting mechanical energy from a __.
a) Heat source
b) Prime mover
c) Solar PV system
d) Chemical activity
b) Prime mover
100: The transformer winding that is connected to the source is called the __ winding.
a) Primary
b) Secondary
c) High-leg
d) Low-leg
a) Primary
100: Overcurrent is current in excess of the equipment ampere rating or ampacity of the wires. What may cause it?
a) Overload
b) Short circuit
c) Ground fault
d) Any of these
d) Any of these
100: What is the resistance of the circuit wires when the wire voltage drop is 7.20V and the current flow is 50A?
a) 0.14Ω
b) 0.30Ω
c) 3Ω
d) 14Ω
a) 0.14Ω (7.20 V ÷ 50 A = 0.144 Ω)
200: In an AC induction motor, what does the stator produce?
a) Rotating magnetic field
b) Explosive force
c) Static electricity
d) None of these
a) Rotating magnetic field
200: What is created by a generator when the electromagnetic field of the rotor cuts through the stator winding?
a) Voltage
b) Current
c) Resistance
d) Power
a) Voltage
200: A transformer has a primary winding of twenty turns and a secondary of ten turns. The winding turns ratio of this transformer is __.
a) 2:1
b) 4:1
c) 5:1
d) 10:1
a) 2:1 (20 turns:10 turns = 2:1)
200: What is the operation of equipment or wires in excess of their rated ampacity called?
a) Overload
b) Short circuit
c) Ground fault
d) All of these
a) Overload
200: What is the current flow in amperes through a 9.50 kW heat strip rated 230V when connected to a 230V power source?
a) 25A
b) 39A
c) 41A
d) 230A
c) 41A (9500 W ÷ 230 V = 41.3 A)
300: The output mechanical work of a motor is rated in horsepower, where 1 hp = __.
a) 746 W
b) 840 W
c) 500 W
d) 600 W
a) 746 W
300: The approximate output current for a single-phase, 22 kVA, 240V generator is __.
a) 50A
b) 70A
c) 90A
d) 100A
c) 90A 22,000 VA ÷ 240 V = 91.67 A ≈ 92 A
300: If the primary phase voltage is 480V and the secondary phase voltage is 240V, what is the voltage turns ratio?
a) 1:2
b) 1:4
c) 2:1
d) 4:1
c) 2:1 (480V:240V = 2:1)
300: Circuit breakers and fuses are intended to interrupt the circuit. They must have an ampere interrupting rating (AIR) __ for the available short-circuit current.
a) Inadequate
b) Sufficient
c) Sustainable
d) None of these
b) Sufficient
300: What is the voltage of a circuit carrying 4.80A supplying a 100Ω resistor?
a) 110V
b) 220V
c) 360V
d) 480V
d) 480V (4.8 A × 100 Ω = 480 V)
400: What is the approximate output in watts of a 15 hp motor?
a) 11 kW
b) 15 kW
c) 22 kW
d) 31 kW
a) 11 kW (15 hp × 746 W = 11,190 W ≈ 11 kW)
400: Voltages in a three-phase circuit originate from a __.
a) Generator
b) Transformer
c) Motor
d) All of these
a) Generator
400: What is the secondary voltage of a 4:1 turns ratio transformer if the primary is 240V?
a) 60V
b) 210V
c) 208V
d) 277V
a) 60V (240 ÷ 4 = 60)
400: GFCI protective devices detect the _ current between circuit wires.
a) Grounded
b) Neutral
c) Imbalance of
d) Phase
c) Imbalance of
400: What is the power loss at a terminal having a resistance of 0.20Ω when carrying 40A?
a) 100W
b) 210W
c) 320W
d) 430W
a) 100W (P = I² × R = 40² × 0.2 = 1600 × 0.2 = 320 W — Correct answer should be c) 320W)
500: When a motor starts, the current drawn is between six and ten times the motor’s nameplate __.
a) Lock-rotor amperes
b) Running amperes
c) Voltage
d) None of these
b) Running amperes
500: What is the secondary current for a fully loaded single-phase, 25 kVA, 480V to 240V transformer?
a) 52A
b) 104A
c) 208A
d) 250A
b) 104A (25,000 VA ÷ 240 V = 104.17 A)
500: Autotransformers use a _ winding for both the primary and secondary.
a) Different
b) Special
c) Separate
d) Single
d) Single
500: Selective coordination of overcurrent protective devices prevents _ power losses to loads not part of the faulted circuit.
a) Intended
b) Unintended
c) Excessive
d) None of these
b) Unintended
500: What is the voltage of a circuit carrying 20.80A supplying a 10Ω resistor?
a) 110V
b) 208V
c) 460V
d) 500V
b) 208V (20.80 A × 10 Ω = 208 V)