UFC 3 -520-01
June 10, 2002
7-2.3.1 Reduced Voltage Starters. Several different designs are available, including
primary resistor, autotransformer, part winding, wye delta, and solid-state. For more
information, re fer to AFPAM 32-1192.
7-2.3.2 Adjustable Speed Drives. If an ASD is required for other reasons, it can
also address motor starting current design needs. Refer to paragraph 7 -3 for additional
information regarding these devices.
7-2.4
Manual controllers can be used within the limitations imposed by the NEC, if
appropriate for the application. MCCs having disconnect devices, branch circuit
overload protection, and controllers mounted in a single assembly can be used where
several motors are grouped in a particular area, as in mechanical equipment rooms. Do
not exceed a control circuit voltage of 150 volts to ground.
7-2.5
If designed for direct control, use control devices--such as thermostats, float
switches, or pressure switches-- to automatically control the starting and stopping of
motors that are designed for that purpose and have adequate kilowatt/horsepower
rating. Typically, these devices should be rated for the motor's horsepower rating to
ensure that the contacts can handle inrush starting current. If the automatic control
device does not have an adequate rating, use a magnetic starter actuated by the
automatic control device. Review the wiring requirements and control scheme for
complex direct digital control circuit; these systems typically require more attention in
the design phase to ensure the system operates as desired.
7-2.6
If the motor starting circuit provides automatic starting, such as by a level
switch or temperature switch, or if the starting device is not in sight, or more than 15.2
meters (50 feet) from the motor and all parts of the machinery operated, design the
power or control circuit so that it can be positively locked open. All motors designed
such that an unexpected starting of the motor might create an exposure of personnel to
injury must have the motor control circuit designed to block automatic reenergization
after a power supply interruption of sufficient duration for moving equipment to become
stationary. Design the motor control circuit so that an operator has to take some action
to restart the motor or e lse have automatic restarting preceded by warning signals and a
time delay sufficient for personnel action to limit the likelihood of injury. This
requirement does not apply to motors with an emergency function where opening of the
circuit could cause less safe conditions. Identify motors that can automatically start with
a caution tag stating, "Caution. Motor will automatically start."
7-2.7
Where combination manual and automatic control is specified and the
automatic control operates the motor directly, use a double -throw, three -position switch
or other suitable device (marked MANUAL-OFF-AUTOMATIC) for the manual control.
7-2.8
Where combination manual and automatic control is specified and the
automatic control device actuates the pilot control circuit of a magnetic starter, provide
the magnetic starter with a three-position selector switch marked MANUAL-OFF-
AUTOMATIC.
7-4
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