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Chapter 3 Manual Starters Objectives • Discuss the operation of manual motor starters • Discuss low voltage release • Connect a manual motor starter • Check a circuit to determine if a motor is drawing excessive current Introduction • Manual starters: – Operator must go to the starter to initiate any change – Some look like a toggle switch with an overload heater – Others are operated by push buttons and may be capable of low voltage protection Fraction Horsepower SinglePhase Starters • Toggle switch lever mounted on front – Used to control the on/off operation – Provides overload protection • Overload heater connected in series with the motor – When current flows, the heater produces heat in proportion to the motor current Fraction Horsepower SinglePhase Starters (cont’d.) • Starters intended to protect motors operating on 240 volts should contain two load contacts – Are intended to control fractional horsepower motors only – Do not provide low voltage release – Do not contain an electrical coil Fraction Horsepower SinglePhase Starters (cont’d.) • Mounting requires little space: – Can be mounted in a single gang switch, conduit box, or directly onto a piece of machinery – Open type can be mounted in the wall and covered with a single gang switch cover plate – Available in different enclosures Fraction Horsepower SinglePhase Starters (cont’d.) • Automatic operation – Sometimes combining the manual starter with other sensing devices is necessary – Pilot device must be equipped with contacts that can handle the rated current • “Line voltage” devices have larger contacts Manual Push-Button Starters • Integral horsepower starters • Two-contact models are intended to control single-phase motors operating on 240 volts, or direct current motors • Three contacts are intended to control three-phase motors Manual Push-Button Starters (cont’d.) • If any overloads trips, a mechanical mechanism will open the load contacts and disconnect the motor from the line • After cooling, it must then be reset by pushing the STOP button Manual Push-Button Starters (cont’d.) • Low-voltage release and low-voltage protection – Both employ a solenoid that senses voltage – A voltage drop disconnects power – Low-voltage release automatically restarts when power is restored; low-voltage protection must be manually reset Troubleshooting • Determine whether the motor is actually overloaded – Bad bearings, shorted windings • Simplest way to determine overload – Find the motor full load current on the nameplate and then check the running current with an ammeter Troubleshooting (cont’d.) • Thermal overloads: – Loose connections – Ambient, or surrounding, air temperature • Set a fan that blows on the starter to help remove excess heat • Vented cover plates