Magnetism & Induction
3 Phase Motors
Miscellaneous
Sizing Motor
Sizing Motor
100
Electromagnetism is used to convert electrical energy into?
Rotating mechanical force.
100
____ is the stationary part of an AC motor that converts electrical energy to the energy of a magnetic field?
Stator
100
A ____ is a device that stores an electrical charge?
Capacitor
100
What article in the NEC refers to Motors, Motor Circuits, and Controllers?
Article 430
100
When unsure to use the Table FLC or Nameplate FLA refer to what NEC section?
430.6(A)(1) & (2)
200
Mutual Induction
200
How do you change the direction of rotation of 3 phase motor?
Interchanging any two of the 3-phase power lines to the motor.
200
A ____ is an electric switch that operates using the centrifugal force created from a rotating shaft which opens the switch and breaks the electrical connection?
Centrifugal Switch
200
Calculate the minimum ampacity for the motor branch circuit conductors at 460v.
Table 430.250 =
7.6 amps x 125% = 9.5 amps
200
What sections of NEC refers to motor disconnecting means?
430.101 through 430.113
300
What happens when an AC sine wave crosses the zero point?
Positive to negative, Magnetism reverses
300
Actual voltage applied to a motor should be within ___% of the motors nameplate rated voltage?
10%
300
What is this drawing representing?
Low Voltage Wiring
300
What size inverse-time-circuit breaker is used for branch-circuit short-circuit and ground fault protection? 230v
Table 430.250 = 15.2 amps
Table 430.52 = 250%
= 38 amps = 40amp breaker
300
What is the maximum rating of the motor branch-circuit short-circuit and ground-fault protection using time delay fuses?
Table 430.248 = 28 amps
Table 430.52 = 175%
= 49 amps = 50 amp fuse
400
What are the requirement of induction?
A conductor, magnetic field, and relative motion.
400
What are the two major components of a magnetic motor starter?
Contactor and Overload Relay
400
This equation represents _____?
Output Power / Input Power =
Motor Efficiency
400
What is the minimum current rating of the motor disconnecting means?
Table 430.248 = 28 amps
430.110(A) = 115%
28 x 115% = 32.2 amps
400
Determine the maximum overload protection using overload relays? 208v
430.32(A)(1) Separate Overload Device
40°C rise, 1.15 SF = 125%
Nameplate FLA = 21 amps
21 x 125% = 26.25A
500
What does the Left Hand Conductor Rule describe?
The direction of a magnetic field around a conductor relative to the direction of the current in the conductor.
500
Apparent power is measured in ____?
Volt amperes or Kilovolt amperes
500
Name to parts of a magnetic motor starter.
Top Half of starter = ___?
Parts of top half = ___ ___ ___?
Bottom Half of starter = ___?
Parts of Bottom Half = ___ ___?
Contactor
Coil, Rated Contacts, Holding Contacts.
Overload Relay
Heaters, NCOL
500
A 230-volt, 3-phase, 25-horsepower squirrel-cage motor and a 230-volt, 30-horsepower synchronous motor are installed on the same motor branch circuit. What is the minimum ampacity of the conductors for this single branch circuit?
Table 430.250, 3-phase
25 hp squirrel-cage = 68 A FLC
30 hp synchronous = 63 A FLC
430.24, branch circuit ampacity = (largest FLC × 125%) + other(s)
= (68 × 1.25) + 63
= 85 + 63
= 148 A
500
What is the maximum standard rating for a time-delay (dual-element) fuse permitted to be used for motor branch-circuit short-circuit and ground-fault protection for a 10-horsepower, 208-volt, single-phase capacitor motor when starting current is a problem?
Table 430.248, single-phase motor
10-hp, 208 V = 55 A
Table 430.52(C)(1), Exception No. 2(b)
Time-delay dual-element fuse = 225%
Rating = 55 × 2.25 = 123.75 A
Next lower standard size OCPD
240.6(A) standard size = 110 A