Which device is specifically used to limit inrush current by presenting high resistance when cold and decreasing as it heats?

Which device is specifically used to limit inrush current by presenting high resistance when cold and decreasing as it heats?

• A. NTC thermistor
• B. Capacitor
• C. Fuse
• D. Inductor

Answer: (A)

Inrush current limiting relies on a component that has a high resistance when cold and becomes less resistant as it heats. An NTC thermistor fits this behavior exactly. When power is first applied, the thermistor is cool, presenting a relatively high resistance that slows the initial surge into the power supply or transformer. As current flows, it heats up, and its resistance drops, allowing normal operation with much less voltage drop and heat after startup. This is different from a capacitor, which initially acts like a short and charges up, causing a surge rather than limiting it through temperature-dependent resistance. A fuse protects by opening on overcurrent, not by changing resistance with temperature. An inductor limits current via its magnetic field and reactance, not because its resistance decreases with temperature.

Inrush current limiting relies on a component that has a high resistance when cold and becomes less resistant as it heats. An NTC thermistor fits this behavior exactly. When power is first applied, the thermistor is cool, presenting a relatively high resistance that slows the initial surge into the power supply or transformer. As current flows, it heats up, and its resistance drops, allowing normal operation with much less voltage drop and heat after startup. This is different from a capacitor, which initially acts like a short and charges up, causing a surge rather than limiting it through temperature-dependent resistance. A fuse protects by opening on overcurrent, not by changing resistance with temperature. An inductor limits current via its magnetic field and reactance, not because its resistance decreases with temperature.