Engineering Manual o.. - HVAC.Amickracing

ELECTRIC CONTROL FUNDAMENTALSMOMENTARY FAST-SLOW-OFFSTART-STOP CIRCUITFigure 37 illustrates a momentary, two-speed, start-stopcircuit with separate windings for fast and slow motor speeds.Pressing the FAST button closes a circuit energizing startersolenoid F for the fast windings. Pressing the SLOW buttoncloses a circuit energizing starter solenoid S for the slowwindings. The holding circuits and the push-button contactsare mechanically interlocked to prevent energizing both sets ofwindings at the same time. Pressing the STOP button opensboth holding circuits and stops the motor.Where a mechanical interlock does not exist between theholding circuits and push-button contacts, the fast speed startcircuit must be opened before energizing the slow speed circuitbecause of the N.C. slow auxiliary contact wired in series withthe fast speed solenoid. A similar situation exists when changingfrom slow to fast.FUSEDDISCONNECTSTARTERL1SOLT1FL2L3FFTRANSFORMERFSFOLOLOLT4FT3FT5T3T5T4T2T1MOTORWINDINGST6FSOLT2FOLT6FSFOLSTOPSLOWFAST(FAST AND SLOWOVERLOADS INSERIES)SFSC2540Fig. 37. Momentary Fast-Slow-Off Start-Stop Circuit.116ENGINEERING MANUAL OF AUTOMATIC CONTROL