OVERLOAD - Any hook load greater than the rated load.
PITCH DIAMETER - The distance, measured through the center of a drum or sheave, from center to center of a rope passed about the periphery of the drum or sheave.
PLUG - To operate a controller in such a manner that the motor line voltage polarity or phase sequence is reversed before the motor rotation has stopped, thereby developing a counter torque which acts as a retarding force.
PLUGGING RELAY - A current relay used on a bridge or trolley control panel which senses current in the motor secondary circuit of an alternating current motor and limits reverse torque of the motor to the first control point until the motor rotation has stopped. In a direct current control panel, the relay performs the same function by establishing a patented sensing circuit at the motor armature. (Sometimes called an anti-plugging relay.)
RAIL, BRIDGE - The track supported by the bridge girder(s), on which the trolley travels.
RAIL, RUNWAY - The track supported by the runway beams, on which the crane travels.
RIGHTHAND END - A reference to parts or dimensions on the viewer's right of the centerline of span, established when facing the drive girder side of the crane.
SECONDARY VOLTAGE - The induced open-circuit voltage in the rotor of a wound-rotor (slipring) motor at standstill, as measured across the slip rings with rated voltage applied to the primary (stator) winding.
SHAFT, CROSS (SQUARING SHAFT) (DRIVE SHAFT) - The shaft(s) extending the length of the bridge, used to transmit torque from the motor to a wheel(s) at each end of the bridge.
SIDE PULL - The portion of the hoist rope pull acting horizontally when the hoist ropes are not operated vertically.
SPAN - The horizontal distance center to center of the runway rails.
SPRING RETURN - A device used on a manual controller, master switch, or pushbutton to cause the unit to return automatically to the neutral position, when released by the operator.
TORQUE, LOCKED-ROTOR - The minimum torque which a squirrel-cage motor will develop at rest, for all angular positions of the rotor, with rated voltage applied at rated frequency. Not applicable to wound-rotor (slipring) motors.
TORQUE, MOTOR BREAKDOWN - The maximum torque which a squirrel-cage or wound-rotor (slip-ring) motor will develop with rated voltage applied at rated frequency, without an abrupt drop in speed.
TORQUE, MOTOR FULL-LOAD - The torque developed by an electric motor (A.C. or D.C.) to produce its rated horsepower at rated full-load speed.
TORQUE, MOTOR PULL-UP - The minimum torque developed by a squirrel-cage or wound-rotor (slipring) motor during the period of acceleration from rest to the speed at which breakdown torque occurs. For squirrel-cage motors with 8% or greater slip, the pull-up torque, the break down torque, and the starting torque are all equal and occur at zero speed.
TWO-BLOCKING - Inadvertent physical contact between the load block and the upper block or other part of the trolley.
WEB PLATE - The vertical plate(s) connecting the upper and lower flanges or cover plates of a girder.
WHEELBASE - The distance from center .to center of the outermost wheels of the bridge or trolley, measured parallel to the rail.
WHEEL LOAD, BRIDGE - The vertical force (without impact) produced on any bridge wheel by the sum of the rated load, trolley weight and bridge weight, with the trolley so positioned on the bridge as to give maximum loading.
WHEEL LOAD, TROLLEY - The vertical force (without impact) produced on any trolley wheel by the sum of the rated load and the trolley weight.