Patent GB-1456451-A (GB)
Title: Circuit breaker with replaceable rating adjuster and interlock means
IPC: H01H73/38
Filed: 1974-01-28
Abstract: 1456451 Circuit breaker overload rating adjustment WESTINGHOUSE ELECTRIC CORP 28 Jan 1974 [30 Jan 1973] 03814/74 Heading H1N A circuit breaker in a housing (Fig. 1, not shown) and comprising a releasable mechanism (29) which can be latched and is tripped by an automatic overload trip arrangement, and manually operable means (75) which enables the releasable mechanism to be re-latched after tripping and which can only be operated to open and close the contacts (31, 43 and 25, 45) when the releasable mechanism is latched, is provided with means for altering the overload setting comprising a removable and replaceable overload rating adjuster, including a resistor connected into solid-state circuitry which responds to overload to effect tripping of the device, and an interlock which automatically maintains the mechanism tripped when the rating adjuster is removed. The circuit breaker contact mechanism is of known type, the over-centre toggle mechanism being latched for manual operation by means of a releasable member (61) which is held by a latching device (67) which forms the subjectmatter of Specification 1,449,992. This is tripped by a magnetic actuator 147 such as that forming the subject-matter of Specification 1,454,354. It is energized for tripping by current transformers in each of the three phases, which on the occurrence of an overload in any phase, feed a current pulse, by means of the circuit shown in Fig. 8, to the operating coil TC2 of the magnetic actuator. This circuit forms the subject-matter of Specification 1,426,855. The overload current at which tripping will occur is determined by the value of the resistor R connected to the collectors of the transistors Q1 and Q2 and this value is adjusted by unplugging the resistor R from the terminals T and replacing it by another of different rating. The replaceable overload rating adjuster 195, Figs. 4 and 7 (and Fig. 6, not shown) comprises the resistance R, in an insulating housing 197, 199, with terminal plug pins 203 and a captive screw 205. It fits into an aperture 207 in the cover 13 of the circuit breaker casing, Fig. 4 (and Fig. 5, not shown) adjacent the circuit board 153 carrying the circuit of Fig. 8. The plugs 203 engage in the terminal sockets T in this board and the captive screw 205 engages in a mounting member 219 which is biased by a spring 223 to bear down upon a leaf spring 211 which in turn bears upon the shoulder of a pin 175 which trips the latching mechanism. When the captive screw 205 is screwed home into the mounting member 219 to secure the rating adjuster it lifts the mounting member thus allowing the leaf spring 211 to lift as shown in Fig. 4. This allows the latch tripping pin 175 to be lifted by the latch resetting mechanism, so that the circuit breaker can be re-set. This interlock feature is the claimed subject of Specification 1,456,452. The casing of the rating adjuster has a locating projection (237, Fig. 6, not shown) which is shaped so that incorrectly rated units cannot be inadvertently fitted. A rheostat may be included in the rating adjuster in series with the resistor R to provide for fine adjustment (Figs. 9 and 10, not shown).