Changing Voltage and Speeds of Single-Phase Motors

Home | Articles | Forum | Glossary | Books


The single-phase motor is available for connection on 110 or 230 V. If the motor is connected for 115 V, it can be reconnected on the factory floor for 230 V. It's also possible to reconnect a motor from 230 V to 115 V. This allows the motor to he used in any voltage application.

Figure 12-42a shows the two coils of the run winding connected in parallel for low voltage. The start winding is then connected in parallel with these coils. The diagram in this figure shows that leads T1, T3, and T5 are connected to L1 and that T2, T4, and T8 are connected to L2. Figure 12-42b shows the connections for high voltage. From this diagram notice that the two coils for the run winding are connected in series. The start winding is connected in parallel across the lower coil (T3-T4) of the run winding. When 230 V is applied to the two coils of the run winding, the voltage divides equally, 115 V across each coil.

The start winding will also receive 115 V from the terminals to which it's connected. From these connections notice that each coil section is rated for 115 V. If the motor is connected for low voltage, all the coil sections are connected in parallel so they will each have 115 V applied to them. When the motor is connected to 230 V, the run winding acts as a voltage divider so that each coil still receives 115 V. The single-phase motor is also available for dual speeds. This type of motor must have the number poles reduced to increase the speed of the motor. In most cases the motor will lose some of its horsepower rating when it's operated on the faster speed, since fewer poles are used.

Fig. 1: (a) Diagram for single-phase motor wired for 115 volts (low voltage). (b) Diagram for single-phase motor wired for 230 volts (high voltage).
Above: Fig. 1: (a) Diagram for single-phase motor wired for 115 volts (low voltage). (b) Diagram for single-phase motor wired for 230 volts (high voltage).

Top of Page previous related article or category Thermal Overload Protector Next related page, article or category

Increasing the Starting Torque of a Single-Phase Motor

Home