CIRCUIT BREAKER WITH ADJUSTABLE LOW MAGNETIC TRIP

摘要

A circuit breaker (1) has a magnetic trip assembly (23) which can be adjusted to trip the breaker for low level overcurrents in the range of five to ten times rated current. The magnet trip includes for each pole of the breaker a helical torsion spring (119) having one torsion arm (123) which biases an armature (111) against an adjusting bar (131) to form a gap (127) between the armature and a stationary magnetic structure (109) in which magnetic flux strong enough to attract the armature and trip the breaker is induced by overcurrent. A second torsion arm (129) of the spring has a first portion which bears against and slides along a pivot member (135) carried by the adjusting bar to adjust the bias force applied to the armature by a given amount per unit travel of the adjusting bar over a low trip current portion of the range of travel of the adjusting bar. A second terminal portion (165) of the second torsion arm of the spring extending at an angle from the first portion (163) engages and slides along the pivot member (135) on the adjusting bar to provide a greater change of bias force per unit travel of the adjusting bar at the higher tripped current settings. Movement of the adjusting bar adjusts the spring bias for all poles of a multiphase circuit breaker simultaneously. The gaps between the armatures and the fixed magnetic structures of all the poles can also be adjusted by camming surfaces (175) on the adjusting bar against which the springs bias the armatures. In an alternative embodiment, the gaps can be adjusted separately for each pole by screws carried by the adjusting bar which bear against camming surfaces formed by twisted tabs (125) on the armatures.