To determine whether to select motor circuit
protectors or molded-case circuit breakers, see
subparagraph Coordination in Part 1.
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Combination motor controller units shall contain [motor circuit protectors]
[molded-case circuit breakers], auxiliary and pilot devices and [a magnetic
contactor with thermal overload relays] [[or] [and] reduced voltage starter
where indicated on the drawings]. The ratings of [motor circuit
protectors,] air circuit breakers, contactors, motor controllers and other
devices shall be as shown on the drawings. All combination motor
controller units shall have short circuit ratings equal to [_____] or
greater. Where control push-buttons, indicating lamps,
"Hand-Off-Automatic" switches, and similar control devices are associated
with a unit, they shall be mounted on the unit compartment door.
Door-mounted components shall not interfere with access within the
compartments. [Molded case circuit breakers for use in combination
starters shall meet the requirements of paragraph MOLDED CASE CIRCUIT
BREAKERS.] [Motor circuit protectors shall be only part of the combination
starters as required by NFPA 70 and shall conform to all requirements of
paragraph MOLDED CASE CIRCUIT BREAKERS, except that trip units shall have
provision for locking the selected trip setting.]
2.6.3.1
Magnetic Contactors
Magnetic contactors shall be of the NEMA sizes indicated on the drawings.
The rating, performance and service characteristics shall conform to the
requirements of NEMA ICS 2 for contactors with continuous current ratings
for the duty indicated. Contactors for motor control shall be rated for
full-voltage starting (Class A controllers). Contactors shall be suitable
for at least 200,000 complete operations under rated load without more than
routine maintenance. The interruption arc and flame shall be minimized by
suitable arc chutes or other means so that no damage will be done to other
portions of the device. The arc chutes, if provided, shall be easily
removable without removing or dismantling other parts. The contacts shall
be easily removable. All current-carrying contact surfaces shall be
silver-surfaced or of other approved material to prevent the formation of
high resistance oxides. The contactor shall operate without chatter or
perceptible hum while energized. Coils shall be suitable for continuous
operation [120-volt ac] [480-volt ac] [125-volt dc] circuits.
Alternating-current contactors shall be three-pole, except where otherwise
noted, and shall be insulated for 600 volts ac and of the electrically-
operated, magnetically-held type. Direct-current contactors shall be
two-pole, suitable for controlling circuits operating at 125 volts dc,
insulated for 250 volts dc, electrically-operated, magnetically-held type
and adequate for full-voltage motor starting service.
2.6.3.2
[Reduced Voltage Starters
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NOTES: Motor loads using reduced voltage starting
must be able to operate with reduced starting torque.
Autotransformer starters should be used when voltage
drop due to motor starting current is a problem.
Solid state starters may also be used. Designer to
determine best alternative.
Solid state starters provide a smooth acceleration
SECTION 16403A
Page 23
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