POWER RELAYS OR CONTACTORS.- The contactor (also called a power relay or motor contactor) is a heavy-duty relay used to control motor circuits. The coil of the relay is in the 115-volt start-and-run circuit, while three of the contacts (designated A, B, and C) are in the 440-volt motor circuit. Contact D is in the run portion of the start-and-run circuit. The D contact supplies an input to the control circuit which indicates that the contact is closed. There are three sizes of contractors (00, 1, and 3) used in gun mounts. Size 1 is shown in figure 5-11.

Figure 5-10.-Tlme-delay relay.

Figure 5-11.-Size 1 contactor.

The main components of the size 1 contactor area coil, an armature, a group of four stationary contacts, a group of four movable contacts (linked to the armature through a crossbar), an inertia shock latch, and an arc suppressor box that encases the contact assemblies.

When the coil energizes, the resultant armature movement pulls the crossbar upward and closes the main contacts (A, B, and C) and the auxiliary contact (D). This action, in turn, completes the 440-vo]t circuit to the associated motor. An inertia shock latch prevents the contactor from closing (if de-energized) or opening (if energized) from inertia shock. When the contactor is subjected to shock, a latch weight moves a slider bar to lock the armature in position momentarily.

The main components of the size 00 and size 3 contractors are basically the same as those of the size 1, except that the size 00 does not have an arc suppressor box. The armature of a size 3 contactor pivots to close its contacts, and it also has five sets of contacts (one more auxiliary contact than the size 1). A kickout spring inside the contactor on the size 3 opens the contacts when the coil de-energizes. This spring also prevents shock or vibration from closing the contactor.

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