A wire from Terminal 3 is connected to the common on the motor windings. Common describes the wire that connects one end of the run winding to one end of the start winding. Current flowing through the common supplies power to both windings, hence it is “common” to both windings. See Figure 25‑13. Three-Wire Overload Connections On open-type motors, a three-wire connection is often used for the overload protector. Power supply is connected to Terminal 1, the run winding to Terminal 2, and the start winding to Terminal 3. See Figure 25‑14. The heater inside the overload is connected in series with the start winding. This connection makes the overload respond quickly to any fault in the start winding, the source of many motor problems. During normal operation, the run winding is protected by the bimetallic disc only. However, if the bimetallic disc opens the contacts between Terminals 1 and 2, the power supply to both windings will be interrupted. Internal Overload Protection Many large hermetic and semihermetic compressors have an overload protector buried inside the motor windings. This overload can sense Compressor (common) Resistance heater Contacts Bimetal Neutral 2 1 3 Goodheart-Willcox Publisher Figure 25‑12. A resistance heater wire, connected in series with the bimetallic element, makes an overload react more quickly. 3 1 Centrifugal switch Run winding Start winding Common Overload Goodheart-Willcox Publisher Figure 25‑13. The overload is in series with the com- mon connection to the run and start windings, allowing the overload to protect against excess current flow through either winding. 3 2 1 N L1 Start winding Run winding Centrifugal switch Goodheart-Willcox Publisher Figure 25‑14. Three-wire connections to the overload use all three terminals. The heater is connected in series with the start winding so the overload reacts quickly to any problem with the start winding. Chapter 25 Motors 493 Copyright Goodheart-Willcox Co., Inc.