Copyright Goodheart-Willcox Co., Inc. 258 Essential Electrical Skills for HVACR: Theory and Labs 13.3 Split-Phase Motors Split-phase motors operate on single-phase power. This type of motor cannot self- start with only single-phase applied. Therefore, single-phase power must be split. This means that two out-of-phase currents must be created. This is illustrated in Figure 13-7 through Figure 13-10 of the previous section. There are four split-phase motors currently used in HVACR applications: • Resistance-start, induction-run • Capacitor-start, induction-run • Permanent split capacitor • Capacitor-start, capacitor-run The differences in these four types are based on their starting and running torque requirements. All types require both a run and a start winding. The rotor rotation direction can be changed by switching the direction of the cur- rent in the start winding in respect to the run winding current direction. See Figure 13-11. However, the motor must have provision to change rota- tion. Manufacturers provide terminals that can be easily exchanged on select motors. These terminals are found in the motor’s terminal board where external power connections are made. The start winding terminals typically identified as terminals 2 and 5 have red and black wires connected to them with quick connect mating terminals. To change the rotor direction, wires must be disconnected and exchanged when reconnecting. For example, if the red wire was on terminal 2, move it to terminal 5 with the black wire on ter- minal 2. Two split-phase motors require the start winding to be disconnected after the motor starts. One method of dis- connecting the start winding is using a centrifugal switch. Centrifugal force acts on objects moving in a circular path. When rotational speed is increased to a certain level, the object travels in a straight path and breaks away from the circular path. The typical centrifugal switch is made with weights attached by springs to the shaft. When the motor reaches from 60% to 75% of rated speed, the weights propel outward away from the shaft. The outward movement of the weights cause a set of contacts to open, 1 1 S N + – L1 S L2 Centrifugal switch Clockwise Rotation 1 1 N S + – L1 S N L2 Centrifugal switch Counterclockwise Rotation N Switch wires to change direction Goodheart-Willcox Publisher Figure 13-11. Rotor rotation direction is changed by interchanging the start winding terminals with respect to the run winding terminals.