26309 Study Guide
If a squirrel cage induction motor draws 2A of current at 240V and is connected for use on 480V, the amperage will be?
1A
If two 10 ohm windings are connected in series for operation on 480V, the total impedance is?
20 ohms
What is the maximum value for short circuit protection for multi motor branch circuits?
250% of the smallest motor
For ordinary motors, the short circuit ground fault protection for non time delay fuses are sized at what percentage of the motor FLC?
300%
The synchronous speed of a 60Hz, three-phase induction motor with two pole is?
3600rpm (formula is 120F/P)
The total resistance of the stator windings in a three-phase motor, if the windings are connected in parallel and the resistance of each winding is 96 ohms, is?
48 ohms
If the stator windings of a dual-voltage motor both have and impedance of 10 ohms and they are connected in parallel, the total impedance is?
5 ohms
The most common number of motor leads found on a three-phase, wye-wound motor is?
9
When sizing equipment grounding conductors for branch circuits of continuous duty motors,?
Combine the rating of each branch circuit OCPD and when applicable the overcurrent protective device
When a motor is oversized, a high degree of overload protection can be provided by sizing the fuses based on?
Full load current of the motor nameplate
The synchronous speed of a motor is the?
Speed at which the magnetic field rotates
The synchronous speed of an induction motor is determined by the number of stator poles and?
The frequency in Hz
The two most common three-phase motor configurations are?
Wye and Delta
If a motor has a current draw of 20A at 240V, what will the ampere be if 480V is applied?
10A
If the total resistance of two motor windings connected in parallel is 24 ohms, with 240V applied to the circuit, how much current will flow?
10A
The maximum recommended size of a dual element time delay fuse for a 50hp, 460V 3 phase motor rated at 65 FLA is?
113.75, next size up is 125(NEC Table 430.52)
A circuit breaker suitable for use as a motor disconnecting means must have a current rating of at least?
115% of the motor full load current
If a 480V three phase motor control center feeds a 50hp motor at 65A, 40hp motor at 52A, and 10hp at 14A, the minimum feeder ampacity is?
147.25A
Of the following motors, the one most likely to have 15 or 18 motor leads is the?
2,400V three-phase motor
With 240V applied to a total parallel impedance of 5 ohms, the current is?
48A
What is an MSCP?
A fuse like device designed for use only in a special type of fusable switch combination motor starter
Good electrical protection for a motor includes both proper overload protection and?
Current limiting short circuit protection
Doubling the voltage on a dual-voltage motor ?
Halves the full-load current
When used for short circuit protection of motor branch circuits what must be adjustable and used in conjunction with combination motor starters?
Instantaneous trip circuit breakers
In addition to short circuit protection, MSCPs also serve as?
Motor disconnecting means
The requirements for torque motors, shaded pole motors, permanent split capacitor motors, and AC adjusted voltage motors can be found in what NEC section?
NEC section 430
Which of the following list the full-load current for three phase motors with a known wire type, horsepower, and voltage?
NEC table 430.250
The type of three-phase motor is determined by the?
Rotor
One of the three factors that will cause a 3 phase motor magnetic field to rotate is that the?
Stator windings around the inside of the motor are arranged in a specific manner to induce rotation
Which of the following is true concerning the starting current of an induction motor if the circuit is energized?
The current rises rapidly
Stator windings can best be described as?
a structure of copper or aluminum coils
The main purpose of motor overload protection is to protect the motor from?
damaging overload currents
To calculate the maximum safe load that a motor may be expected to carry continuously at its rated voltage and frequency, the service factor is multiplied by the ?
horsepower rating
If the total resistance of two motor windings connected in parallel is 20 ohms and 240 volts is applied to the circuit, how much current will flow?
12A
The most effective method of power factor correction is the installation of?
Capacitors
