Figure 7-13. - Control circuit components.

Figure 7-14. - Three-phase motor controller diagram.

difficult to understand. As you already know, most electrical circuits are represented as a wiring diagram or a line diagram. Work through the examples given throughout this chapter. This practice will improve your skills in reading and understanding electrical diagrams. If the diagrams are too complex, break them down to a more elementary diagram. These diagrams are your key to understanding how a machine operates and how to repair it when it breaks.

TWO-WIRE CONTROL. - Two-wire control provides no-voltage release or low-voltage release. Two-wire control of a starter means that the starter drops out when there is a voltage failure and picks up as soon as the voltage returns. In figure 7-15, the pilot device is unaffected by the loss of voltage. Its contact remains closed, ready to carry current as soon as line voltage returns to normal.

The phrases no-voltage release and two-wire control should indicate to you that an automatic pilot device, such as a limit switch or a float switch, opens and closes the control circuit through a single contact.