Motors Final Review pt 2/4 Flashcards
A motor’s nameplate voltage rating is the ____ voltage that should be connected to the motor for best operating performance.
Optimal
The actual voltage applied to a motor should be within plus or minus ____ of the motor’s nameplate rated voltage.
10%
The ___ rating of a motor is abbreviated “HZ”
frequency
The ____ rating is a multiplier that represents the amount of load that can be placed on a motor, beyond the rated load, without causing damage.
service factor
A ____ is a short circuited winding, consisting of a single turn of copper wire which acts on only a portion of the stator winding.
shaded-pole
If a capacitor start motor is to be reversed often, then a ____ or ____ can be used to reverse the current through the start winding, with respect to the run windings.
Drum switch or
foot switch
When the voltage of a dual-voltage motor is doubled (115 V to 230 V) the current is ____.
reduced by half
The ____ of a motor support(s) the motor shaft.
bearings
In a two-pole, single phase motor, the start winding is placed ____ degrees from the run winding.
90
When rotation is not possible because the stator’s field and the rotor’s field are equal or parallel to one another, the rotor is ____.
locked in place.
The primary difference between single-phase motors and three-phase motors is the ____.
start windings
Starting large horsepower motors can result in significant ____ on a distribution system that can damage other electrical equipment connected to the system.
voltage drop
Motors that are started at reduced voltage must be switched to line voltage in order to reach ____.
full speed
Full-voltage starting has ____ starting current and ____ starting torque.
High /
High
____ starting devices are small, durable, and have no contacts.
Solid-state
The listed full load table current for a 7 1/2 hp squirrel cage motor that operates ate 3-phase, 208V is ____.
24.2 Amps
Table 430.250
What is the minimum ampacity of a single branch circuit that supplies four 1 1/2 hp, 408V, 3-phase induction type squirrel cage continuous duty motors?
12.75 Amps
Table 430.250
3.0 x 1.25 + 3 + 3 + 3 = 12.75 A
The motor branch circuit, short circuit, and ground fault protective device shall be capable of carrying the ____ current of the motor.
starting
Determine the rating of the motor branch circuit short circuit and ground fault device for a 5 hp, 208V, 3-phase, squirrel cage induction motor using delay fuses.
30 Amp
175% x 16.7amps (Table 430.250)
Determine the maximum rating of the motor branch circuit rating short circuit and ground-fault protective device, when starting current is not a problem, for a 5 hp, 115V, single phase, induction motor using time delay fuses.
100 Amp
56A x 175% (Table 430.248 -FLC)
Where the values for branch circui short-circuit and ground-fault protective devices determined by Table 430.52 do not correspond to the standard sizes or ratings of fuses, non-adjustable circuit breakers, thermal protective devices or possible settings of adjustable circuit breakers, a higher size, rating, or possible setting that does not exceed the next ____ standard ampere rating shall be permitted.
higher
The provisions of overload protection are not required where this protection might introduce ____.
additional or increased safety
Generally, in order to calculate the proper size of a separate motor overload protection device for a continuous duty motor, the ____ current of the motor is used.
Nameplate
Separate motor overload protection shall be based on the ____ current rating.
motor nameplate
A _____ is a condition that is not guarded against the use of motor overload protection.
line to ground fault condition
