NTC thermistor

A resistor whose resistance falls as it warms.

Schematic letter: RT / NTC
Unit / key rating: Ohm (Ω) @ 25 °C

Pinout

2 leads: No polarity.

Real photos

What is it for?

An NTC (negative temperature coefficient) thermistor's resistance drops as temperature rises. Its value is given at 25 °C (e.g. 10 kΩ).

It has two main uses: measuring temperature (air-cons, chargers, 3D printers) and limiting inrush current in power supplies. The latter uses big disc NTCs of a few ohms when cold.

Things to watch out for

⚠ Don't hold it with your fingers while measuring: your body heat changes the reading.
⚠ If the NTC at a supply's input opens, the device looks completely dead; it should read a few ohms when cold.

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