chapter 3 manual starters. objectives discuss the operation of manual motor starters discuss low...

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 Single-Phase 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 Single-Phase 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 Single-Phase 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 Single-Phase 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