Rated field voltage (or field resistance and rated current) for
shunt-wound and compound-wound motors;
Power supply designation which is the basis of the rating.
To meet NEMA requirements, the following information must be provided for
AC motors in addition to that required by the Code:
Manufacturer's type and frame designation;
Maximum ambient temperature;
NEMA nominal efficiency (except for Design D squirrel cage motors
and wound-rotor motors);
Service factor (except for wound-rotor motors);
NEMA wording regarding overtemperature devices (except for wound-
18.104.22.168 Anti-Condensation Heaters. On newer outdoor cranes, an
anti-condensation heater is installed in every generator and drive motor.
de-energized whenever rotation occurs.
Control Equipment. Control equipment is utilized on a crane for motor
operation. Equipment to directly influence the speed and direction of rotation of
each drive motor is mounted on the control panel. Examples of such equipment are
contactors and relays, electronic conversion units, transformers, protective
devices, and terminal blocks. The control panel is mounted in an enclosure.
External devices which interface with panel mounted equipment are resistors, limit
switches, master switches and pendent pushbutton stations, and safety devices.
On newer outdoor cranes, a thermostatically controlled anti-condensation
heater is installed in each control panel enclosure.
Contactors and Relays. Contactors are used for line, directional, and
accelerating functions. In a constant potential DC system, the line contactor,
when energized, connects the motor branch circuit to one side of the line. The
directional contactors are used to connect the motor branch circuit to the other
side of the line and are arranged so as to cause current to flow through the motor
armature in one direction or in the opposite direction while not changing
direction of current flow through the field; this changes the direction of the
A series brake is released when 40 percent or less of full load current
flows through the motor branch circuit. The release of a shunt brake is
interlocked with the line and directional contactors. The accelerating contactors
shunt out or add in various segments of the series resistance, affecting motor
speed for a given load. The less resistance there is in the armature circuit, the
faster the motor rotates.
A relay is used in the control circuit to ensure that the line-to-line
voltage is suitable. It is referred to as a "UV" relay. In addition to its
principal function of shutting down the crane if the line-to-line voltage is too