and a three-phase inverter. Select diodes and power transistors
so that their current ratings are not less than 200 percent of
full load motor current. Provide motor overload protection
utilizing a thermal sensitive device embedded in its windings.
Energize each crane drive's electro-mechanical brake by a dedicated
contactor controlled directly by the pushbuttons on the pendent
pushbutton station; i.e., when both of the pushbuttons for a drive
are in the OFF position the brake shall be set and when either of
them is in any drift or speed point position the brake shall be
released. Provide dynamic braking. Connect resistors to the
controller's DC bus whenever motor regeneration causes the DC
voltage to rise to a predetermined unacceptable level. Provide
resistors continuously rated at a minimum of 125 percent of the
full load motor current.
b.
Hoist Control
Feed control circuit from a single phase, air cooled, double wound
transformer with a grounded metal screen between the primary and
secondary windings of the transformer.]
2.4.3
Protection
Not less than that required by NEMA ICS 3, CMAA 70, NFPA 70, 29 CFR 1910.147,
29 CFR 1910.179, 29 CFR 1910.306 and all applicable provisions of 29 CFR
1910. Provide enclosed type circuit breaker for crane disconnect. The
main line contactor shall be the floor operated disconnect. Provide for
lockout/tagout of all hazardous energy sources.
2.4.4
Resistors
**************************************************************************
NOTE: Include "125 percent of" only if electronic
controls have been selected previously.
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Provide resistors rated for continuous duty operation based upon [125
percent of] the motor nameplate amperes and fabricated of corrosion
resistant metal; the use of "wire wound" type resistors is prohibited for
segments of 8 ohms or less. Mount resistors in substantial, ventilated
enclosures constructed entirely of non-combustible materials. Provide
resistors with terminals fitted in the coolest position in the enclosure.
2.4.5
Reactors
Provide reactors rated for continuous duty operation based upon the motor
nameplate amperes. Select reactors for 60 Hz operation and having taps for
field adjustment of inductance so as to permit achievement of the optimum
acceleration characteristics for the drive. Secure the cores and the coils
of the reactors to prevent any permanent change in the relative position of
the parts. Ground the core to the case or make electrically accessible,
except for toroidal coils and nonmetallic cores such as ferrites.
2.4.6
Limit Switches
Provide upper and lower limit switches which de-energize the hoist motor.
Lift limiting and overload limiting devices which use a clutch to stop
motion shall not be furnished with the hoist.
SECTION 14636N
Page 15
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