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

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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 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 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 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 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

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