1 1 ECET 211 Electric Machines & Controls Lecture 8 Motor Control Circuits Text Book: Electric Motors and Control Systems , by Frank D. Petruzella, published by McGraw Hill, 2015. Paul I-Hai Lin, Professor Electrical and Computer Engineering Technology P.E. States of Indiana & California Dept. of Computer, Electrical and Information Technology Purdue University Fort Wayne Campus Prof. Paul Lin Lecture 8 Motor Control Circuits Part 1. NEC Motor Installation Requirements • Sixing Motor Branch Circuit Conductor • Branch Circuit Motor Protection • Selecting a Motor Controller • Disconnecting Means for Motor ad Controller • Providing a Control Circuit Part 2. Motor Starting • Full-Voltage Starting of AC Induction Motors • Reduced-Voltage Starting of Induction Motors • DC Motor Starting Prof. Paul Lin 2 Part 3. Motor Reversing and Jogging • Reversing of AC Induction Motors • Reversing of DC Motors • Jogging Part 4. Motor Stopping • Plugging and Anti-plugging • Dynamic Breaking • DC Injection Breaking • Electromechanical Friction Brakes Part 5. Motor Speed • Multispeed Motors • Wound-Rotor Motors
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ECET 211 Electric Machines & Controls
Lecture 8 Motor Control Circuits
Text Book: Electric Motors and Control Systems, by Frank D.
Petruzella, published by McGraw Hill, 2015.
Paul I-Hai Lin, Professor
Electrical and Computer Engineering Technology
P.E. States of Indiana & California
Dept. of Computer, Electrical and Information Technology
Purdue University Fort Wayne Campus
Prof. Paul Lin
Lecture 8 Motor Control Circuits
Part 1. NEC Motor Installation
Requirements
• Sixing Motor Branch Circuit
Conductor
• Branch Circuit Motor
Protection
• Selecting a Motor Controller
• Disconnecting Means for
Motor ad Controller
• Providing a Control Circuit
Part 2. Motor Starting
• Full-Voltage Starting of AC
Induction Motors
• Reduced-Voltage Starting
of Induction Motors
• DC Motor Starting Prof. Paul Lin 2
Part 3. Motor Reversing and
Jogging
• Reversing of AC Induction
Motors
• Reversing of DC Motors
• Jogging
Part 4. Motor Stopping
• Plugging and Anti-plugging
• Dynamic Breaking
• DC Injection Breaking
• Electromechanical Friction
Brakes
Part 5. Motor Speed
• Multispeed Motors
• Wound-Rotor Motors
2
Lecture 8 Motor Control Circuits
Part 1. NEC Motor Installation
Requirements
• NEC Article 430 covers
application and installation of
motor circuits including
conductors, short-circuit, and
ground fault protection, starters,
disconnects, and overload
protection.
• Motor Brach Circuits – include
the final overcurrent device
(disconnect switch and fuses or
circuit breaker), the motor
starter and associated control
circuits, circuit conductors, and
the motor.
Prof. Paul Lin 3
Figure 8-1 Basic elements of a motor
branch circuit that the NEC addresses
Motor Control Circuits – NEC Motor Installation
Requirements
Sizing Motor Branch Circuit
Conductor
NEC Article 430, Part II
Article 430.6
• Installation requirements for motor
branch circuit conductor
• A single motor used in a
continuous-duty application must
have an ampacity of not less than
125 percent of the motor’s Full-
Load Current (FLC)
Article 430.247 through 430.250
• Conductor ampacity must be
determined by NEC Tables
430.247 through 430.250 and is
based on the motor nameplate
horsepower rating and voltageProf. Paul Lin 4
Full-Load Current (FLC) –
indicates the use of NEC table
rating
Full-Load Amperes (FLA) –
indicates the actual nameplate
rating
Article 430.247 through
430.250
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Lecture 8 Motor Control CircuitsPart 1. NEC Motor Installation Requirements:
Sizing Motor Branch Circuit Conductor
Example 8-1
Problem: using your edition of the NEC, determine
the minimum branch circuit conductor ampacity
required for each of the following motors:
(a) 2 hp, 230V single-phase motor
(b) 30 hp, 230V, three-phase motor with a
nameplate FLA rating of 70A
Solution:
(a) NEC Table 430-248 shows the FLC as 12 A.
Conductor ampacity required is 12 x 125% = 15A
(b) NEC Table 430.250 shows the FLC as 80A.
Conductor ampacity required is 80 x 125% = 100A
Prof. Paul Lin 5
http://www.automationdirect.com/
adc/Shopping/Catalog/Motors
Lecture 8 Motor Control CircuitsPart 1. NEC Motor Installation Requirements: Sizing Motor Branch
Circuit Conductor
Feeder Conductors supplying two or more motors must have:
An ampacity not less than 125 percent of the FLC rating of the
highest-rated motor, plus,
The sum of the FLC ratings of the other motor supplies.
Ampacity of the conductor => NEC Table 310.15(B)(16) => American