1. Field
The disclosed and claimed concept relates generally to circuit interrupters and, more particularly, to an improved tool and calibration machine employed in calibrating a thermal trip apparatus of a circuit interrupter.
2. Related Art
Numerous types of circuit interrupters are known for use in diverse applications. One type of a circuit interrupter is a circuit breaker having an operating mechanism that moves the circuit breaker between an ON condition, an OFF condition, and a TRIPPED condition. Such circuit breakers typically also include a trip mechanism that causes the operating mechanism to move the circuit breaker from the ON condition to the TRIPPED condition. The trip mechanism can include any one or more of a variety of components that can trigger the operating mechanism to open a set of separable contacts in any of a variety of overcurrent and under-voltage conditions. One type of known component of a trip mechanism is a thermal trip apparatus which includes a bimetal element that becomes heated in a persistent overcurrent condition and accordingly trips the circuit breaker.
While such thermal trip apparatuses have been generally effective for their intended purposes, they have not been without limitation. As is generally understood in the relevant art, a bimetal element deflects in a predetermined fashion upon heating. However, due to manufacturing variations and tolerances, the thermal trip apparatus of any given circuit breaker must be calibrated during the manufacturing process. That is, each circuit breaker's thermal trip apparatus is adjusted so that it causes the circuit breaker to trip in response to a predetermined persistent overcurrent condition, by way of example. In certain circuit breakers, the calibration process has involved an inelastic (i.e., plastic) deformation of a frame within the circuit breaker upon which the bimetal element is carried. Such an inelastic deformation occurs by receiving a rectangular-shaped object into an interior region of the circuit breaker and rotating the rectangular-shaped object to engage and inelastically deform the frame until the bimetal element has moved sufficiently that it is calibrated to trigger the operating mechanism at a predetermined current level.
However, if the frame has been deformed beyond the calibration point, the deformation of the frame cannot be reversed without substantial reworking of the circuit breaker, with the result that an unacceptably high number of rejected circuit breakers must be discarded because they were over-deformed during the calibration operating and cannot be easily calibrated thereafter. It thus would be desirable to provide an improved system for calibrating a thermal trip apparatus of a circuit interrupter.