NTC is a negative temperature coefficient. NTC thermistor can provide variable resistance according to temperature change. With the increase of temperature, the resistance is from high to low, allowing current to pass through. When used to suppress surges, it provides an additional series resistance when energized. As the thermistor heats itself and the current flows, the resistance drops to a negligible amount in a stable state, allowing normal current flow

PTC is a positive temperature coefficient. PTC thermistor can also provide variable resistance according to temperature. With the increase of temperature, the resistance increases from low to high, blocking the overcurrent. Specific scenarios require PTC thermistors to be superior to NTC thermistors. These include equipment with near zero reset time, extreme temperature conditions, and systems with frequent short circuits.