SELECTOR SWITCHES

Many machines and process operations are designed so as to function in any one of the several ways. For example, the three different modes of operation may be Manual, Semi-automatic and Automatic. A selector switch will enable the operator to predetermine the manner in which his machine is to operate. As with push-button switches, selector switches also have two main parts, the mechanical actuator and the contact block. Selector switches are usually of the maintained position type, although momentary spring return selectors are also available. Selector switches can have single break contacts or double break contacts. The symbols for both these type of contacts have been shown in Figs. 2.28 and 2.29.

The selector switches are generally made for four positions. As the number of positions increase to four, manufacturer provide charts of tables which display positions of the selector switch actuator. Fig. 2.30 shows a four position selector switch. Note the use of × under the position number. This indicates that the contact in line with × is closed in that position. Below position 1 (Fig. 2.30) × is against contact B and C i.e.,in position 1 contact Band Care closed.

In position 2 contacts B and D will close, further in position 3 contact A and D will close and in position 4 contacts A and C will close.

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