Which term denotes the third winding on a transformer used as a second control winding?

• A. Servo
• B. Thermistor
• C. Tertiary Winding
• D. Torque

Answer: (C)

In transformer design, the extra winding that sits as the third winding beyond the primary and secondary is called a tertiary winding. It’s often used to provide an isolated, auxiliary source of voltage for control circuits or other auxiliary power needs without loading the main secondary. That makes it the correct term for a third winding used as a second control winding. The other terms don’t fit because a servo is a type of control mechanism, a thermistor is a temperature-dependent resistor, and torque is a mechanical force, none of which describe a transformer’s third winding.