normally specified for outdoor cranes. Type 12
enclosures are specified for exceptionally dirty
environments.
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Power rectifiers shall be provided where required to convert ac to dc.
Active semiconductor devices shall be silicon type. Rectifiers for motor
control system shall be three-phase full wave rectifiers. Rectifiers for
brakes shall be single-phase full-wave or three-phase full-wave rectifiers.
A single rectifier may be used in lieu of several smaller rectifiers;
brakes shall be supplied from a different rectifier than the other
equipment. Protective enclosures shall conform to the requirements of NEMA
ICS 6 Type [_____]. Rectifying elements shall be hermetically-sealed and
mounted on heat sinks cooled by natural convection or by mechanical means.
Minimum protection for rectifiers shall consist of transient surge
suppressors, and 100,000 AIC current-limiting 700V rectifier type fuses in
the ac line. Minimum protection for main power rectifiers shall include a
line isolation transformer of the type specifically designed for use with
static conversion units. Individual diode sets and thyristors shall be
protected by fuses on the ac side. Each rectifier bridge used in brake
circuits (including overload protection) shall be rated for continuous-duty
at a minimum of 150 percent of load rating, and for 1 minute at a minimum
of 300 percent of load rating. Each rectifier or SCR bridge used in the
[dc constant potential control system] [or in] [dc variable voltage] shall
be rated for continuous-duty at a minimum of 100 percent of the load
rating, and for one minute at a minimum of 200 percent of load rating
following 8 hours at 100 percent load. The dc rated output voltage shall
not exceed 460 volts.
2.4.4
Motors
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NOTE: Specify hoist motor temperature sensors for
hoists subject to low speeds for long periods
(greater than 3 minutes) and hoists carrying
critical loads; edit paragraphs as required. Motor
heaters are desirable for outdoor cranes, unheated
warehouse service cranes, or any other condensing
high-humidity application. Select a motor from the
following types and coordinate with the desired
control type.
Select industrial motors for CMAA 70, Class A, B, C
and D cranes, as follows:
a. For critical load handling, self-excited
alternator with electrical load brakes or emergency
dynamic braking is preferred.
b.
Select crane type motors for ac motors.
c. Select 800 Series dc mill type motors or dc
industrial motors for dc motors.
d. If crane and/or industrial type motors are
specified, select NEMA MG 1.
Select mill motors for CMAA 70, Class E cranes, as
follows:
SECTION 14630A
Page 30
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