(3600 rpm), medium speed uses four poles (1800 rpm), and low speed uses all six poles (1200 rpm). One leg of the power supply is connected to the common terminal and the capac- itor. The other side of the power supply is connected to the tap for the desired speed. Unless a selector-type switch is used, each unused tap is capped with a wire nut and sealed with electrical tape to prevent the motor windings from becoming grounded by the unused wires. Only one end of the start winding is available for connection to a capacitor by the technician. The other end of the start winding is wired at the factory. A power supply that is parallel to the start winding is provided, regardless of the speed (tap) selected. Most manufacturers color-code the external wires for making connections to multi-speed motors. See Figure 25‑45 for the color codes. 25.7 Three-Phase Motors Three-phase induction motors are common in commercial applications because they are smaller and more powerful than single-phase motors of equal horsepower. Furthermore, they are cheaper to operate, have fewer problems, and are easier to connect and control. Because the 230 V power supply can vary from 208 V to 230 V depending on location, a lot of motors have been designed to run within that range. The voltage listed on their data plate could read 208–230 V. This type of motor does not need to have its wiring changed. Some dual voltage motor’s data plate could show 115/208–230 V. This motor would need to be wired one way for 115 V and another way for 208–230 V. 25.6 Multi-Speed Motors Multi-speed motors are very common in heating, cooling, and refrigeration systems. In contrast to the two wires used in single-speed motors, multi-speed motors have several wires. A multi-speed motor is necessary in applications that require different speed operations, such as a window air conditioner with a fan that operates at high, medium, or low speeds. Many furnace blower motors are multi-speed. Multi-speeds allow more air to be moved during the cooling season (high speed) than during the heating season (low speed). Motor speed is determined by the number of poles in the run winding. The multi-speed motor has different taps (wires) that make it possible to select the number of poles being used. See Figure 25‑44. A high-speed tap uses two poles Low Med-low Med-high High Run winding Start winding Run capacitor PSC motor Resistance added by windings in series with main motor windings L2, Neutral, or Common R S C L1 Multi-Speed, Single-Phase PSC Motor Goodheart-Willcox Publisher Figure 25‑44. Different numbers of poles are used for each speed on a multi-speed motor. Connections are made to the common terminal and the proper tap for a desired speed. A selector switch may be installed for ease of changing from one speed to another. Chapter 25 Motors 509 Copyright Goodheart-Willcox Co., Inc.