Patent ID: 8031455

Claim:
A system comprising: a circuit protective device located in an electrical circuit, the circuit protective device having a time-current characteristic curve, wherein an accumulated thermal loading of the circuit protective device is determined at a first point on the time-current characteristic curve, the first point corresponding to a first current which is greater than a nominal current rating of the circuit protective device, the accumulated thermal loading based on both the first current and an amount of time that the circuit protective device is rated to carry the first current; an isolation device located in series with the circuit protective device in the electrical circuit; and a controller configured to sense current conducted by the circuit protective device, to determine an estimated thermal loading of the circuit protective device, and for current values less than the first current and greater than the nominal current rating of the circuit protective device, to provide a control signal to activate the isolation device to open the electrical circuit when the estimated thermal loading of the circuit protective device at least equals the accumulated thermal loading, wherein the accumulated thermal loading is employed by the controller as a maximum thermal loading of the circuit protective device at each current value less than the first current and greater than the nominal current rating of the circuit protective device, and wherein the circuit protective device is configured to open the electrical circuit independent of the isolation device in response to an overcurrent condition in the electrical circuit as determined by the time-current characteristic curve.