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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