Importance

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Abstract

Overcurrent protection arrangements including a relay comprising two coils wound on a common magnetic core and a PTC device coupled in parallel with the relay contacts. The arrangement comprises a circuit interruption element which has a normal state which permits the flow of a normal circuit current, I.sub.NORMAL, to pass through the system, and a fault state which permits the flow of at most a reduced current, I.sub.REDUCED, substantially less than I.sub.NORMAL. A first control element is coupled in series between the power supply and the load, and is functionally linked to the circuit interruption element so that when the current through the first control element increases from I.sub.NORMAL to a relatively high current, I.sub.FAULT, the first control element can convert the circuit interruption element into the fault state. A second control element is coupled in parallel with the circuit interruption element, and is functionally linked to the circuit interruption element so that if the circuit interruption element is converted to the fault state, the second control element can cause the circuit interruption element to remain in the fault state as long as the current through the second control element is at least I.sub.REDUCED. The parallel combination of the circuit interruption element and second control element are coupled in series with the first control element. The relay contact functions as the circuit interruption element, and the two relay coils function as the first and second control elements.

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First Claim