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.
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.