Multiple Push-Buttons Stations

Objectives

After studying this unit, the student will be able to:

• Read and interpret diagrams using multiple push-button stations

• Draw diagrams using multiple push-button stations

Connect multiple push-button stations

The conventional three-wire, push-button control circuit may be extended by the addition of one or more push-button control stations. The motor may be started or stopped from a number of separate stations by connecting all start buttons in parallel and all stop buttons in series. The op­ eration of each station is the same as that of the single push-button control in the basic three-wire circuit covered in unit 29. Note in figure 38-1 that pressing any stop button de-energizes the coil. Pressing any start button energizes the coil.

When a motor must be started and stopped from more than one location, any number of start and stop buttons may be connected. Another pos­ sible arrangement is to use only one start-stop sta­ tion and several stop buttons at different locations to serve as emergency stops.

Multiple push-button stations are used to control conveyor motors on large shipping and re­ ceiving freight docks.

FIGURE 38-1 Three-wire control using a momentary contact. multiple push-button stationFIGURE 38-2

REVIEW QUESTIONS

1. Using the line diagram in figure 38-2, determine the number of wires controlling the three-phase motor. The conduit layout plan indicates the sections of conduit for which the quantity of wires is to be determined.

2. Referring to figure 38-2, select the minimum size conduit for each run. Use the appropriate locally enforced electrical code-national, state, county, or city.

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