Thermal overload trip apparatus and method for adjusting trip sensitivity thereof

A method for adjusting a trip sensitivity of a thermal overload trip apparatus, in the thermal overload trip apparatus comprising:

• bimetals for providing a mechanical displacement according to an overload in a circuit, a shifter mechanism for transferring the mechanical displacement of the bimetals as a driving force, a trip mechanism driven to a trip position by the driving force from the shifter mechanism when the overload is generated in the circuit, release lever mechanism having one portion rotatably installed to contact the shifter mechanism so as to receive the driving force from the shifter mechanism and another portion installed to contact the trip mechanism, so that the release lever mechanism presses the trip mechanism and drive the trip mechanism to the trip position when there is the driving force from the shifter mechanism, or the release lever mechanism releases the trip mechanism when there is no driving force from the shifter mechanism, when the overload is generated in the circuit, an adjusting lever having a portion for rotatably supporting the release lever mechanism so as to operate the release lever mechanism to be horizontally moved by the rotation, an adjusting knob having an upper surface provided with a setting groove and a lower portion provided with a cam portion so as to set a trip operation position according to a rated current, and an adjusting screw connected to the adjusting lever to rotate the adjusting lever so as to independently adjust sensitivity to the trip operation current regardless of manipulation of the adjusting knob, the method comprising:
• setting an initial position of the adjusting knob;
• assembling components forming the thermal overload trip apparatus;
• conducting a predetermined overcurrent to the thermal overload trip apparatus assembled in the assembling step for a predetermined time;
• and
• adjusting the adjusting screw by rotating the adjusting screw until a trip operation occurs under a state that the adjusting knob is maintained at the initially set position.