Fuses and PTC Thermistors

For most, the only deciding factor between choosing a fuse or PTC thermistor is preference. However, certain characteristics and applications make one item better than the other. Depending on the type of work the device will be used for, PTC thermistors may work better than fuses or fuses may work better than PTC thermistors.

When making the decision between a fuse and a PTC thermistor, the leakage current is one aspect to consider. The leakage current of a thermistor can range from about a hundred milliamps at rated voltage to several hundred milliamps at lower voltages. The leakage current for the fuse works differently. The fuse interrupts the current flow. The open circuit results in zero leakage current when subjected to the overload.
Interrupting rating is another characteristic to research before making a decision. The PTC thermistor is rated for a maximum short circuit current at rated voltage. The rated voltage is the maximum current that the device can handle, but unlike a fuse, it will not interrupt the current flow.

The temperature rating of the two devices differs. The maximum operating temperature of PTC thermistors is 85 degrees Celsius while the maximum operating temperature for fuses is 125 degrees Celsius. Both devices will require derating when the temperature is above 20 degrees Celsius.

Voltage rating is another characteristic to consider. PTC thermistors are not rated above 60V. Fuses are rated up to 600V. Resistance is one more feature to consider when deciding between the two devices. Similarly rated PTC thermistors have twice, and sometimes more, the resistance of fuses.

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