Current limiting circuit breaker

Abstract

A current limiting iron wire resistor having a transformable resistance for a current limiting circuit breaker. Each pole of the circuit breaker includes said resistor in parallel with a pair of auxiliary contacts for current limiting which are in series with a pair of main contacts to open the circuit. The main contacts are separable upon operation of a thermally and electromagnetically operable tripping mechanism, and the auxiliary current limiting contacts separate only on occurrence of a high amplitude fault current above a preselected threshold value. When that value of fault current is reached, the tripping mechanism and associated components which operate the auxiliary current limiting contacts serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the current limiting resistor. The resistor is formed in a bent-back serpentine shape to reduce inductance of the parallel resistor circuit which would otherwise be very high with the magnitudes of fault current involved, and to also balance the mutual electromagnetic forces among various sections of the resistor. The resistor also includes integrally formed flattened terminals, and intermediate terminal pieces welded to the flattened terminal of the iron wire resistor between the resistor and the copper conductors leading to and from the resistor at each terminal end. The intermediate terminal pieces have a resistivity characteristic between that of the copper conductors and the iron wire resistor.