A positive temperature coefficient (PTC) device is a passive component used to protect against overcurrent faults. In this paper, dimensions of a PTC device connected in series with a circuit breaker that can act as a current limiter has been calculated. When the current flowing through the device exceeds the current limit, the PTC device warms up above a threshold temperature and the electrical resistance of the PTC device suddenly increases several orders of magnitude to a tripped state where the resistance will typically be hundreds or thousands of ohms, greatly reducing the current. This feature allows power system to use a cheap circuit breaker in series with the PTC device to disconnect the circuit. In this paper, by helping heating equations and simulations with finite element method, the PTC device cross-sectional area and its thickness has been calculated.

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