When testing windings of a single phase induction motor, how does the start winding resistance compare to the run winding?

When testing windings of a single phase induction motor, how does the start winding resistance compare to the run winding?

• A. About the same as that of the run winding
• B. About half that of the run winding
• C. 3 to 4 times greater than that of the run winding
• D. About 500 ohms

Answer: (C)

When testing the windings of a single-phase induction motor, the start winding typically has a higher resistance compared to the run winding. This is due to the start winding being designed to handle higher inrush currents and operate for a shorter duration during the motor's startup phase. The increased resistance in the start winding—often measured as being 3 to 4 times greater than that of the run winding—helps to limit the current flow during startup and allows the motor to accelerate to operating speed before the start capacitor is switched out of the circuit. Once the motor reaches a sufficient speed, the start winding is no longer needed, so having higher resistance avoids excess current draw through this winding. The other options suggest either a resistance similar to or less than that of the run winding, which does not align with the operational characteristics of induction motors. The specific value of 500 ohms is arbitrary and does not universally apply as windings can have various resistances based on size, construction, and design. Thus, while resistance values can differ widely based on the specific motor, the general principle is that the start winding resistance is indeed significantly greater than that of the run winding.

When testing the windings of a single-phase induction motor, the start winding typically has a higher resistance compared to the run winding. This is due to the start winding being designed to handle higher inrush currents and operate for a shorter duration during the motor's startup phase.

The increased resistance in the start winding—often measured as being 3 to 4 times greater than that of the run winding—helps to limit the current flow during startup and allows the motor to accelerate to operating speed before the start capacitor is switched out of the circuit. Once the motor reaches a sufficient speed, the start winding is no longer needed, so having higher resistance avoids excess current draw through this winding.

The other options suggest either a resistance similar to or less than that of the run winding, which does not align with the operational characteristics of induction motors. The specific value of 500 ohms is arbitrary and does not universally apply as windings can have various resistances based on size, construction, and design. Thus, while resistance values can differ widely based on the specific motor, the general principle is that the start winding resistance is indeed significantly greater than that of the run winding.