The 140U-QTD3-D45 trip unit from Allen-Bradley is a trip unit for molded case circuit breakers. It is compatible with 3-pole Q-frame circuit breakers which are part of the Bulletin 140U series and which have a continuous current rating of 450 Amps. The 140U-QTD3-D45 trip unit is a fixed thermal–adjustable magnetic type of trip unit. The magnetic trip range for the 140U-QTD3-D45 trip unit is 2250 to 4500 Amps. The installation of the 140U-QTD3-D45 trip unit into a compatible circuit breaker should not be performed while the circuit breaker is energized. Substantial equipment damage or severe injury can occur due to contact with the energized electrical equipment. The technicians should always verify that no voltage is present before performing any maintenance activity. Generally accepted safety precautions should always be followed.

The cover on the 140U-QTD3-D45 trip unit is sealed at the factory to prevent people from tampering with the module’s calibration. The thermal trip mechanism on the 140U-QTD3-D45 trip unit is designed to cause breaker tripping within 2 hours for 135% overload and in less than 2 hours for higher overloads. For the magnetic trip mechanism, the breaker trip occurs instantaneously for currents that exceed the magnetic trip setting. The trip current times are the same for DC or AC voltage in the overload trip region. The magnetic trip setting on each of the circuit breaker poles can be set with a screwdriver. For the magnetic trip region, the DC trip thresholds can be configured at 40% higher levels compared to the AC trip thresholds. The calibration for the 140U-QTD3-D45 trip unit is carried out at 40 degrees Celsius for AC and DC voltage at 50/60 Hertz.