Download AN-MC-004: How to wire a motor starter

THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT IS
SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. We do not guarantee that the data is
suitable for your particular application nor we do assume any responsibility for them in your application.
SUBJECT: How to wire a motor starter
Number:
AN-MC-004
Date Issued: 2/08/2005
Revision:
Original
A motor starter is a combination of devices to allow an induction motor to start, run and stop
according to commands by an operator or a controller. Typically an induction motor will run by a
voltage of 230 Volt or 460 Volt, 3 phase 60 Hz in USA and be controlled by a control voltage of 115
Volt AC or 24 Volt DC. Several other combinations are possible in USA or other countries and are
easily derived from the methods shown in this document.
The motor starter must have a contactor to open or close the flow of energy to the motor and an
overload relay to protect the motor against thermal overload. Other devices for disconnecting and
short-circuit protection are necessary, typically a circuit breaker or fuses. The short-circuit protection
is not shown here.
The contactor is a switch with 3 poles whose poles are closed by the application of a control voltage
to the coil. When the coil is energized the 3 poles are closed and are kept closed as long as the coil is
energized. The contactor is a special relay specifically designed for motor control, but can be used
for resistive loads; in the case of resistive loads it is possible to handle the thermal current, which is
more than the current of a motor. Since the motor has inductance, the breaking of the current is more
difficult and the contactor has to be derated.
The overload relay is a device that changes the status of a normally closed contact from ON to OFF
when the current going thru any of the 3 phases increases above a set point. This device is designed
to provide overcurrent protection to a motor.
This document shows step by step the process of wiring the FUJI series of contactors that ADC sells.
The main combinations are:
a) Full voltage non reversible 3 phase motors.
b) Full voltage reversing 3 phase motors
c) Single phase motors
d) Wye-delta open transition
We will show the basic circuit and in some cases pictures on how to connect the wiring. The pictures
are shown here to teach the methods and are not intended to show how a panel is professionally
wired. The examples show only one size of contactor with a coil of 24 VDC but the concept is valid for
all the available sizes.
WARNING! Use the instructions of each specific device. Failure to do so may result in electric shock
or damage.
This set of pictures shows a set of elements you will need:
Contactor
Overload relay
Auxiliary contact block
Start/stop pushbutton
Page 1
THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT IS
SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. We do not guarantee that the data is
suitable for your particular application nor we do assume any responsibility for them in your application.
a) Full voltage non reversible 3 phase motors.
The following diagram is shown for a 3-wire control with 24 VDC control voltage: The picture shows
the same arrangement. We need a contactor, an auxiliary contact block, an overload relay, a normally
open start pushbutton, a normally closed stop pushbutton and a power supply with a fuse (Not shown
on the picture).
POWER
SUPPLY
24 VDC
+ -
L1
L2
L3
DISCONNECT
L1
53
L2
L3
A2
CONTACTOR
M1
A1
54
T1
T2
T3
95
OVERLOAD
96
T1
T2
T3
3 PHASE
MOTOR
Page 2
THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT IS
SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. We do not guarantee that the data is
suitable for your particular application nor we do assume any responsibility for them in your application.
b) Full voltage reversible 3 phase motors.
The diagram is shown on the following figure for a 3-wire reversing control with 24 VDC control
voltage: The picture shows the same arrangement. We need here two contactors, two auxiliary
contact blocks, an overload relay, a mechanical interlock, two normally open start pushbuttons, a
normally closed stop pushbutton and a power supply with a fuse (Not shown on the picture)
L1
L2
L3
POWER
SUPPLY
24 VDC
+ -
DISCONNECT
L2
A2
M1
A1
T1
54
L1
L3
L2
L3
MECHANICAL
INTERLOCK
L1
53
FORWARD
CONTACTOR
T2
T3
53
A2
REVERSE
CONTACTOR
M2
A1
T1
T2
T3
54
95
OVERLOAD
96
T1
T2
T3
3 PHASE
MOTOR
Mechanical interlock shown mounted on
the side of contactor
Page 3
THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT IS
SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. We do not guarantee that the data is
suitable for your particular application nor we do assume any responsibility for them in your application.
c) Full voltage single phase motors.
The diagram is shown on the following figure for a 3-wire control: The picture shows the same
arrangement. . We need here a contactor, an overload relay, one auxiliary contact block, a normally
open start pushbutton, a normally closed stop pushbutton and a power supply with a fuse (Not shown
on the picture)
L1
L2
POWER
SUPPLY
24 VDC
+ -
DISCONNECT
53
L1
L2
L3
A2
CONTACTOR
M1
A1
54
T1
T2
T3
95
OVERLOAD
96
T1
T2
T3
1 PHASE
MOTOR
Page 4
THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT IS
SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. We do not guarantee that the data is
suitable for your particular application nor we do assume any responsibility for them in your application.
d) Wye-delta open transition 3-phase motors.
The following diagram is shown for a 3-wire control of a delta-star connection:. We need here three
contactors, an overload relay, one auxiliary contact block, a normally open start pushbutton, a
normally closed stop pushbutton, a on delay timer of 0-20 second and a power supply with a fuse
L1
L2
L3
POWER
SUPPLY
24 VDC
+ -
DISCONNECT
53
L1
L2
L3
L1
L2
L3
M1
L2
L3
A2
M2
M3
A1
A1
54
L1
A2
A2
T1
T2
T3
T1
T2
T3
T1
T2
T3
A1
T1
T2
A2
TR
A1
T3
95
OVERLOAD
96
T6
3 PHASE
MOTOR
T5
T4
Page 5