Control Systems
for Cooling Tower
Fan Motors
TR-CS91
Control Systems for Cooling Tower Fan Motors
Contents
Page
Motor control required by electrical codes ............................................................................ 3
Wiring diagrams – symbols and general forms ..................................................................... 4
Control enclosures – NEMA types ........................................................................................ 5
Sizing short-circuit protection ................................................................................................ 6
Disconnect (safety) switch .................................................................................................... 7
Circuit breaker ....................................................................................................................... 8
Combination starter ............................................................................................................... 9
Lightning arrester .................................................................................................................. 9
Manual controller ................................................................................................................... 9
Magnetic controller ................................................................................................................ 9
Across-the-line starters ....................................................................................................... 10
Reduced voltage starters .................................................................................................... 11
Reconnectable starters ....................................................................................................... 14
Special features .................................................................................................................. 15
Control of magnetic starters ................................................................................................ 16
Control for motor heating .................................................................................................... 17
Motor overload protection ................................................................................................... 18
Sizing of motor-overload protection .................................................................................... 18
Soft start motor controller .................................................................................................... 21
Variable frequency drive ..................................................................................................... 21
Programmable controllers ................................................................................................... 22
Purchasing information ....................................................................................................... 23
Wiring diagram of single speed motor with time delay ........................................................ 24
Wiring diagrams of two speed motors with various special features .............................. 25-32
Note: This file was revised in 91. This is not it, it is the original from PageMaker 2. Check over the illustrations
carefully to find which Fig was revised. DL 6-26-95.
1
List of Tables
Table
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Page
Diagram symbols and letters .................................................................................... 4
Motor connections ..................................................................................................... 4
Motor design voltages ............................................................................................... 5
Locked rotor code letters .......................................................................................... 6
Max. rating or setting of motor branch-circuit protective devices .............................. 6
Recommended dual-element fuse sizes ................................................................... 7
Typical circuit breaker sizes ...................................................................................... 7
Typical disconnect switch ratings .............................................................................. 8
Standard fuse sizes .................................................................................................. 8
HP ratings for manual starters .................................................................................. 9
Characteristics and costs of magnetic starters ....................................................... 10
HP ratings for magnetic starters ............................................................................. 11
HP ratings for high voltage controllers .................................................................... 11
Average motor amps & conductors for 200 V & 230 V ........................................... 20
Average motor amps & conductors for 460 V & 575 V ........................................... 20
2
Motor Control Required by
Electrical Codes
This section describes the various protective devices, controls, and
enclosures required for this equipment by most electrical Codes.
Refer to the Codes for alternates which are allowable under certain
conditions.
1.
2.
3.
4.
Use three Running Overcurrent units.
Note: Items 1 through 4 are available in a “pump panel” or
combination starter.
5. Conductors supplying a single motor must have a carrying
capacity not less than 125% of motor full load current.
Conductors supplying more than one motor must have a
carrying capacity not less than 125% of full load current rating
of the highest rated motor plus the sum of the full load current
ratings of the rest of the motors. Voltage drop for conductors
must not exceed 3% on the branch circuit.
Any conductor intended only for grounding purposes must be
colored green unless it is bare. Grounded current carrying
conductors must be white or natural gray color. All ungrounded
conductors of the same color must connect to the same ungrounded feeder conductor. The conductors for systems of
different voltages must be different colors.
6. Non-Fused Disconnect Switch — Not required if Item 1 can lock
in open position or is within sight from* motor.
Motors and control boxes must be grounded.
*
Item Contained In
Required Devices
Disconnecting Means — to disconnect motor and controller
from the circuit. It must either open all ungrounded conductors
and be in sight from* controller or it must lock in the open
position. This design must indicate whether switch is open or
closed. The disconnect must be a switch rated in horsepower
or a circuit breaker of the inverse time or instantaneous trip
type. The disconnect, either switch or breaker, for 600 volts or
less motor circuits must be ampere rated for at least 115% of
full load current. It must also be capable of interrupting stalledrotor current.
Motor Feeder — Short-Circuit Protection — to protect the
motor-branch-circuit conductors, the motor control apparatus,
and the motors against overcurrent due to short circuits or
grounds. There must be one in each ungrounded conductor. It
must carry motor starting current, but not over 400% of full load
current. See Tables 4 and 5 for sizing.
Motor Controller — to start and stop the motor. Select the
controller for motor basic HP and voltage. See Tables 10, 11,
14 and 15.
Overload Protection — to protect the motor, control apparatus
and the branch-circuit conductors against excessive heating
due to motor overloads, stalled rotor and excessive cycling.
Select overloads sized at 125% or less of motor full load current
for motors with service factor of at least 1.15. Overload size
must not exceed 115% of full load current for all other motors.
“in sight from” — must be visible and not more than 50 feet distant.
3
Electrical
Supply
Fusible
Safety Switch
or
Circuit Breaker
Manual or
Magnetic
Starter
Conductors
Non-Fused
Disconnect Switch
In Sight from Motor
Motor
Wiring Diagrams
There are two common types of wiring diagrams. The
control equipment supplier provides the standard
“Wiring Diagram”, showing the physical layout of
components and wiring. These diagrams depict the
exact connections required. Each manufacturer uses
unique connection points and physical layout, so each
drawing applies only to one manufacturer.
in the simplest manner with no attempt to show physical layout. This requires separation of the coils from
their contacts. A letter designation ties coil “S” and
contact “S”. Only “Elementary Diagrams” appear in this
manual. All cooling tower motors and control enclosures must be grounded, even though grounding
connections do not appear in this manual. The diagram symbols are shown below:
“Elementary Diagrams” show the operation of a circuit
Table 1 - Diagram Symbols and Letters
Temperature
Actuated Switch
NO*
NC*
Selector Switch
2 Position
3 Position
A1
A2
X
X
Low High
Push Buttons
Single Circuit
Double Circuit
NO
NC
NO
NC
A1 X
A2
X
Hand Off Auto
A1
A1
A2
A2
R
Contacts
Timed Contacts - Contact Action
Retarded When Coil is
Energized
De-Energized
NO
NC
NO
NC
Instant Operating
NO
NC
Pilot Light Transformer
Letter
Iron Core
Indicates
Color
Coil
Overload Relay
Thermal
A.C. Motor
Single
Three
Phase
Phase
*NO - normally open, NC - normally closed - contact position when not energized, pushed, etc.
F - Forward
LF - Low Forward
CR - Control Relay
OL - Overload
R - Reverse
LR - Low Reverse
M
- Program Timer
LOL - Low Overload
H - High
HF - High Forward
TR - Time Relay
HOL - High Overload
L - Low
T1,T2 - Motor Terminal
L1,L2 - Line Terminals
By far, the largest percentage of cooling tower motors
are three phase squirrel cage induction type. Only
these motors appear in the diagrams. For reference,
the three phase motor winding connections most often
used on cooling tower motors appear below. To
reverse a three phase motor, change any two of the
three leads (L1, L2, and L3).
Table 2 - Motor Connections
3 Phase 2 Speed Consequent
Pole (1 Winding) Variable Torque
3 Phase Single Speed
Dual Voltage “Y” (most common) Connection
T3
T6
T9
T1
T4
T7
T4
T8
T5 T2
High Voltage
Connection
T1
Low Voltage
Connection
T3
L1
L2
L3
L1
L2
L3
Low Speed
Connection
T1
T2
T3
T1
T2
T3
L1
L2
L3
T1
T2
T3
T7
T8
T9
T7
T8
T9
T1
T2
T3
T6
T4
T5
T4
T5
T6
T4
T5
T6
T6
T4
T5
L1
L2
L3
4
T2
T5
T6
High Speed
Connection
Control Enclosures
of a rod larger than .250" diameter. Live
parts must be at least 4" from the nearest
drain hole.
The National Electrical Manufacturer’s Association
(NEMA) has established standard types of enclosures
for control equipment. Types most commonly used
with cooling towers are described below.
Type 1
Type 3
General Purpose — This enclosure is
intended primarily to prevent accidental
contact with the control apparatus. It is
suitable for general purpose application
indoors under normal atmospheric conditions. It serves as protection against dust
and indirect, light splashing. It is not dustproof.
Type 4
Water-tight — A water-tight enclosure must
exclude water. It must pass a hose test.
This enclosure is adequate for outdoor use
on a cooling tower. It is usually a gasketed
304 stainless steel enclosure. Type 4X is a
water-tight corrosion resistant enclosure that
will pass a 200-hour salt fog test.
Type 7
Hazardous Locations — Class I Air Break
— This enclosure meets the application
requirements of the National Electrical Code
for Class I, Group A, B, C, or D hazardous
locations. These locations may contain
specific types of flammable gases or vapors.
Refer to the Code for more complete definitions of hazardous locations*. Type 7
enclosures are intended for indoor use but
are sometimes used outdoors on cooling
towers.
Type 9
Hazardous Locations — Class II — This
enclosure is designed for use in Class II
(combustible dust), Group E, F, or G areas.
Dust-tight, Rain-tight and Sleet (Ice)
Resistant — This enclosure is intended for
use outdoors to protect the enclosed equipment against windblown dust and water. It is
not sleet (ice) proof. This enclosure must
have watertight conduit connections, mounting means external to the equipment cavity,
and locking provision.
Type 3R Rain-tight — This enclosure is intended for
use outdoors to protect the enclosed equipment against rain. It is not dust, snow or
sleet (ice) proof. When completely and
properly installed, this enclosure prevents
entrance of rain above the level of the lowest
live part. The 3R enclosure prevents the
entrance of a rod .125" in diameter except at
drain holes. Drain holes will not permit entry
Type 12 Industrial Use — This enclosure is used for
industrial applications to prevent entrance of
foreign materials such as dust, lint, fibers, oil
seepage, or coolant seepage.
*The Code defines hazardous locations in Division 1 and Division 2. In general, starters for either location division must be in
explosion-proof enclosures. Motors for Division 1 locations must also be explosion-proof. Motors for Division 2 locations can
be any enclosure, so long as motor does not employ sliding contacts, centrifugal switches or other types of switching mechanisms, or integral resistance devices.
Table 3 - Motor Design Voltages
Power System
Voltages
120
208
240
480
600
2400
4160
4800
6900
Point of Utilization
(Motor Design) Voltage
115
200
230
460
575
2300
4000
4600
6600
5
Disconnect Means and Short Circuit Protection
Sizing Short-Circuit Protection
A properly sized device serving as both disconnect
means and short circuit protection must:
(1) Carry normal circuit current continuously
(2) Safely switch the circuit under normal or
abnormal conditions
(3) Prevent overcurrents of a predetermined
magnitude for a particular time interval, and
(4) Automatically and safely interrupt current of
any magnitude that the system can produce.
letter and full load current of the motor to properly size
the short circuit protection for a given motor. These
values appear on the motor name plate.
Table 4 lists the locked rotor kilovolt amperes for code
letters appearing on motor name plates. Table 5 lists
the maximum rating or setting of motor branch circuit
protective devices.
Actual locked rotor current of a motor might approach
600% of full load current. However, the proper size
fuse or circuit breaker will not go out on a normal motor
start.
Either a circuit breaker or fusible disconnect switch can
serve as a disconnect means and short-circuit protection. The designer must know the locked rotor code
Table 4 - Locked Rotor Code Letters
Code Letter
A
B
C
D
E
F
G
H
J
K
KVA per HP
0-3.14
3.15-3.54
3.55-3.99
4.0-4.49
4.5-4.99
5.0-5.59
5.6-6.29
6.3-7.09
7.1-7.99
8.0-8.99
Code Letter
L
M
N
P
R
S
T
U
V
KVA per HP
9.0-9.99
10.0-11.19
11.2-12.49
12.5-13.99
14.0-15.99
16.0-17.99
18.0-19.99
20.0-22.39
22.4-and up
Table 5 - Rating or Setting of
Motor Branch-Circuit Protective Devices
Type of Motor
Nontime
Delay
Fuse
Max.
Percent of Full Load Current
Dual Element
Instantaneous
(Time Delay)
Trip
Fuse
Breaker
Max.
RecomMax.
mended
All AC single-phase and polyphase squirrel cage and
synchronous motors with fullvoltage, resistor or reactor
starting:
No Code Letter
Code Letter F to V
Code Letter B to E
Code Letter A
Where max. rating in table
above is not sufficient for
starting current of motor the
max. rating can be increased to
these percent values
300
300
250
150
400% not
exceeding
600 amps
175
175
175
175
225%
6
125
125
125
125
Inverse
Time
Breaker
Max.
Recommended
700
700
700
700
1300%
250
150-225%
250
150-225%
200
150-200%
150
150%
400% (with full
load current less
than 100 amps)
300% (with full
load current
greater than 100
amps)
Disconnect (Safety) Switch
Disconnect switches are rated by amperage and
horsepower. A disconnect switch for a motor load is
horsepower rated. It must carry 115% of motor full
load current continuously and must be capable of
interrupting motor stalled-rotor current. Many fusible
switches have three horsepower ratings: standard
fuse, dual element fuse, and non-fuse. See Table 8 on
Page 8.
Manufacturers differ slightly in horsepower rating of
their switches. Typical values follow:
Table 6 - Recommended Dual Element Fuse Size
for Overload and/or Short Circuit Protection
of Three Phase Motors with a 1.15 or Larger Service Factor
Voltage
200 Volts
HP
1/2
3/4
1
1 1/2
2
3
5
7 1/2
10
15
20
25
30
40
50
60
75
100
125
150
200
250
Full
Load
Amps
2.3
3.2
4.1
6.0
7.8
11.0
17.5
25.3
32.2
48.3
62.1
78.2
92.0
119.6
149.5
177.1
220.8
285.2
358.8
414.0
552.0
Fuse Size
Overload
Short*
& Short
Circuit
Circuit
Protection
Protection
Only
2.8
4
4
5.6
5
8
7
12
9
15
12
20
20
30
30
45
40
60
60
80
70
100
90
110
110
150
125
175
175
200
200
250
250
300
350
400
400
500
500
600
230 Volts
Full
Load
Amps
2.0
2.8
3.6
5.2
6.8
9.6
15.2
22
22
42
54
68
80
104
130
154
192
248
312
360
480
460 Volts
Fuse Size
Overload
Short*
& Short
Circuit
Circuit
Protection
Protection
Only
2.5
3.5
3.5
5
4.5
6.25
6.25
9
8
12
12
15
17.5
30
25
40
35
50
50
70
60
90
80
110
100
125
125
150
150
200
175
200
200
300
300
350
350
450
405
500
600
Full
Load
Amps
1.0
1.4
1.8
2.6
3.4
4.8
7.6
11
14
21
27
34
40
52
65
77
96
124
156
180
240
Fuse Size
Overload
Short*
& Short
Circuit
Circuit
Protection
Protection
Only
1.25
1.8
1.6
2.5
2.25
3.2
3.2
4.5
4
6
5.6
9
9
15
12
20
17.5
25
25
40
30
50
40
50
50
70
60
80
80
110
90
125
110
150
150
175
175
200
200
250
300
350
300
350
* Based on wire size in Tables 14 and 15 for RH, RHW, RVH, THW, THWN, & XHHW wire.
Table 7 - Typical Circuit Breaker Available Sizes
15
20
25
30
35
40
45
50
60
70
80
Thermal Magnetic
90
450
100
500
125
600
150
700
175
800
200
900
225
1000
250
1200
300
1400
350
400
Amp
Rating
3
7
15
30
50
100
150
7
Instantaneous Trip
Trip
Amp
Range
Rating
8-28
225
18-70
400
50-180
600
100-350
800
150-580
300-1100
750-1500
Trip
Range
300-2250
500-4000
625-9000
625-9000
500
Table 8 - Typical Disconnect Switch Horsepower Rating
240V - 3 Phase
Switch
Ampere
Rating
30
60
100
200
400
600
Standard
Fuse
3
7.5
15
25
50
75
Dual
Fuse
7.5
15
30
50
125
200
480V - 3 Phase
Non
Fuse
7.5
15
30
50
125
Standard
Fuse
5
15
25
50
100
150
Dual
Fuse
15
30
60
125
250
400
Standard ampere ratings are 30, 60, 100, 200, 400,
600, 800, and 1200 amperes. Disconnect switches are
available in NEMA Type 1, 3, 3R, 4, 7, 9 and 12
enclosures.
600V - 3 Phase
Non
Fuse
20
50
75
125
250
400
Standard
Fuse
7.5
15
30
60
125
200
Dual
Fuse
20
50
75
150
350
500
Non
Fuse
20
60
100
150
350
500
elements.
Good practice dictates using dual-element fuses rather
than one-time fuses. Dual-element fuses interrupt
higher fault currents, generate less heat in the control
box, and permit use of smaller fuses for better protection. In addition, if a fuse clip is loose on a one-time
fuse, the case can carbonize and fail when the fuse
blows. A loose clip on a dual-element fuse will cause
the fuse to blow before the case can carbonize.
Do not use plug type fuses at voltages greater than 125
volts between conductors except in a grounded neutral
system with less than 150 volts from conductors to
ground. Therefore, they are inappropriate for most
three phase systems. Cartridge type fuses are available with either renewable or non-renewable fuse
Table 9 - Standard Fuse Sizes (Amperes)
250 or 600 Volts
1
3
6
10
15
20
25
30
Single Element
35
100
40
110
45
125
50
150
60
175
70
200
80
225
90
250
300
350
400
450
500
600
0.1
0.15
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.125
1.25
1.4
1.6
1.8
2.0
2.25
Dual Element
2.5
6.25
2.8
7
3.2
8
3.5
9
4.0
10
4.5
12
5.0
15
5.6
17.5
20
25
30
35
40
45
50
60
70
80
90
100
110
125
150
175
200
250
300
350
400
450
500
600
Circuit Breaker
Circuit breakers used for motor protection usually have
both thermal and magnetic trip elements. The thermal
elements protect on overloads where inverse time
tripping is desired. The magnetic trip elements instantly operate the breaker in case of dangerous
overload or short-circuit faults. Usually circuit breakers
do not operate as fast as fuses at high overcurrents,
but operate faster on normal overloads.
They do not have to be replaced when operated. They
also prevent operating the motor single phase. Circuit
breakers can also be equipped for remote operation.
Low voltage (600 volts and less) circuit breakers are of
the air break type. Both oil and air type breakers are
available for high voltage systems. Air circuit breakers
are rated 15, 20, 30, 40, 50, 60, 70, 90, 100, 125, 150,
175, 200, 225, 250, 300, 350, and 400 amps. They are
available in NEMA 1, 3R, 4, 7, 9 and 12 enclosures.
Circuit breakers offer certain advantages over fuses.
8
Combination Starter
A combination starter includes circuit breakers and
disconnect switches as part of the motor controller.
equipment. Install arresters on the incoming side as
near as practical to the piece of equipment to be
protected. Connect one arrester element to each
ungrounded lead.
Lightning Arrester
Usually, to protect a motor, it is necessary to use a
secondary class arrester along with a surge-absorbing
capacitor. A secondary class arrester is designed for
secondary distribution systems such as those supplying motors. Arresters consist of a spark gap and a
device to limit or quench the spark. Each manufacturer
uses his own method or material to limit the spark.
Lightning arresters are usually rated for the maximum
phase-to-phase and phase-to-ground voltage.
Lightning damage to motors and control equipment is
usually caused by high voltage induced in the power
line rather than lightning hitting the motor or control
directly.
Lightning can cause immediate failures or it can
weaken insulation, causing failures at a later date. In
areas where thunderstorms are frequent, it is advisable
to install lightning arresters to protect motors and other
Motor Controller
Manual Controller
Manual Controllers consist of snap-action switch(es)
and overload(s). They are available in NEMA 1, 4, 7,
9, and 12 enclosures. Standard sizes appear in Table
10.
Manual controllers are available for reversing or twospeed two-winding motor control. Single phase
controllers are available with selector switch and pilot
light.
Table 10 - Horsepower Ratings for Across-the-Line Manual Starters
NEMA
Size
M-0
M-1
M-1P
60 Hz
200 or
230 V
3
7.5
Horsepower at:
Three Phase
50 Hz
60 Hz
380 V
480 or 575 V
5
5
15
10
Single Phase
50 or 60 Hz
50 or 60 Hz
115 V
230 V
1
2
2
3
3
5
Magnetic Controller
Types of Magnetic Starters
The motor controller normally used on cooling towers is
a magnetic starter. The standard magnetic starter uses
a magnetic coil to close contacts and springs and/or
gravity to open them. Some type of pilot device, such
as a push button or float switch, actuates the magnetic
coil. The main types of magnetic starters are acrossthe-line, reduced voltage, and reconnectable.
use of reduced voltage or reconnectable type starters
for larger horsepower motors. Reduced starting
current and torque, and increased starting time typify
reduced voltage and reconnectable type starters.
Therefore, the designer must allow sufficient torque to
accelerate the load and to keep starting time short
enough to avoid overheating the motor.
Power company limitations on inrush current dictate the
9
Table 11 - Characteristics and Costs of
Common Magnetic Starters Used for Squirrel-Cage Induction Motors
Acrossthe-Line
Y
V
IS
IS
TS
C
Connection
Phase Voltage
Starting Current (phase)
Starting Current (line)
Starting Torque
Approx. Cost Comparison
Primary
AutoPart
Resistance Transformers
Winding
Y
Y
Y
KV*
KV
V
KIS
KIS
.6 TO .8 iS
KIS
K2IS
.6 TO .8 iS
K2TS
K2TS
.4 TO .48 TX
4.2
4.3
3.0 (2 steps)
(closed
transition)
Star Delta
Y
.58V
.333 IS
.333 IS
.333 TS
5.2
(closed
transition)
*“K” is a constant equal to the reduced voltage over the full line voltage.
Across-the-Line Starters: Across-the-line starters are
the most widely used. The transformer must have
enough capacity to allow the motors to be started this
way. The motor leads receive full voltage as soon as
the pilot device energizes the magnetic coil in an
across-the-line starter.
Table 12 lists sizes of across-the-line magnetic starters
(including reversing) for use with single or multi-speed
variable-torque squirrel cage induction motors (nonplugging or non-jogging duty).
Standard Single Speed Across the Line Starter
with Hand-Off Auto Selector Switch, Push Button
(Three-Wire) and Thermostat (Two-Wire) Control
B1 STOP
START
OL
F
L1
F
B2
L2
L3
F
F
F
FUNCTION at 60°F
B2
B1
X
X
Hand
M
Typical Current and Torque Curves
for Design “B” Induction Motor
10
Off Auto
Table 12 - Horsepower Ratings for Across-the-Line Magnetic Starters
Single Speed and Multi-Speed Variable & Constant Torque
Horsepower at:
Size
of
Starter
00
0
1
1P
2
3
4
5
6
7
8
9
Continuous
Current Rating
Amperes
9
18
27
36
45
90
135
570
540
810
1215
2250
200 V
60 Hz
1.5
3
7.5
—
10
25
40
75
150
—
—
—
Three Phase
230 V
380 V
60 Hz
50 Hz
1.5
1.5
3
5
7.5
10
—
—
15
25
30
50
50
75
100
150
200
300
300
—
450
—
800
—
Single Phase
460 or 575 V 50 or 60 Hz 50 or 60 Hz
60 Hz
115 V
230 V
2
1/3
1
5
1
2
10
2
3
—
3
5
25
3
7.5
50
100
200
400
600
900
1600
Table 13 - Horsepower Ratings for High Voltage Controllers
and Line Contactors
Size of Controller
&
Contactor
H2
H3
Continuous
Current Ratings
Amperes
180
360
Horsepower Rating Induction Motors
Three Phase
2200-2400 Volts
4000-4800 Volts
700
1250
1500
2500
Reduced Voltage Starters
Primary Resistance Starters: Reduced voltage
starters are either primary resistance type or autotransformer type. The pilot device energizes the
magnetic coil of a primary resistance starter, connecting the motor to the line through resistors. The resistors normally limit the motor voltage to 65% or 80% of
normal voltage. A timer, energized at the same time as
the motor, times out and picks up the run contactor
which in turn connects the motor directly across the line
at a predetermined time interval.
This type of starter limits the inrush current, gives
smooth motor and load acceleration, and provides a
higher starting cycle. Disadvantages of this starter are
the physical size of the starter and resistors and the
power loss in the resistors. Primary resistance type
starters are called “close transition starting units.”
11
2 Wire Control
STOP
1
L1
START
2
F
L2
OL
3
L3
F
TR
TR
F
F
F
S
S
S
RES
RES
RES
OL
S
S
Motor
Typical Wiring Diagram of
Primary Resistance Starter
Typical Current and Torque Curves
with 65% Voltage on First Step
for Design “B” Induction Motor
Auto-transformer Starters: Auto-transformers reduce
the starting voltage in this type of starter. The advantages of this type of starter are:
The starter contains several voltage taps. The designer may select the correct reduced voltage for each
application. For motors up through 50 HP, 65% and
80% voltage taps are included. For larger horsepower
motors, 50%, 65% and 80% voltage taps are included.
The transformer ratio reduces the line current for a
given torque.
Both open-circuit transition and closed-circuit transition
auto-transformer starters are available.
At a predetermined time, the timer opens the lines to
the primary of the auto-transformer, then connects the
motor directly across the line. Disadvantages of this
type starter are: high cost, low power factor, complete
loss of power when the motor is disconnected from the
auto-transformer, and high inrush current when the
motor is connected across the line.
Closed-circuit transition: Three transformers are first
connected in wye and the motor is energized through
the transformer taps. After a timed interval, the wye
connections open, leaving the transformer secondary
winding in series with the motor. The motor is then
connected directly across the line and the transformers
are disconnected. Full voltage induces a lower current
peak and complete loss of power does not occur.
Open-circuit transition: A timer and the motor are
energized simultaneously through the transformer tap.
Reconnectable Starters
12
Stop
Start
2 Wire Control - Use Dotted Lines and
Remove Jumper 3 to 4
3
L1
TR
F
TR TR
4
TR
L2
L3
F S
S
F
S
S
S
F
F
OL
S S
OL
OL
T2
T1
OL
T3
Motor
Typical Wiring Diagram
of Auto-Transformer Starter
with Open-Circuit Transition
Typical Current and Voltage Curves
with 65% Voltage on First Step
for Design “B” Induction Motor
2 Wire Control
Stop
Start
L1
L2
TR1
F
TR1
S
TR1
L3
TR1
S
S
F
F
S
T
T
F
F
OL
T
T
OL
OL
T2
T1
Motor
OL
T3
Typical Wiring Diagram
of Auto-Transformer Starter
with Closed-Circuit Transition
Typical Current and Voltage Curves
with 65% Voltage on First Step
for Design “B” Induction Motor
13
Part-winding Starters: Reconnectable starters can be
either part-winding, or star delta type. Part-winding
starters require that the motor stator winding must be
made up of two or more circuits connected in parallel
for normal operation. Standard 230/460 volt motors,
15 horsepower and larger, are generally suitable for
part-winding starting at the lower voltage. Check first
with the motor manufacturer.
half. The locked rotor current on the first step is
approximately 60% to 65% of full locked rotor amps.
The locked rotor torque is approximately 46% to 49%
of full locked rotor torque. Part-winding starting is
primarily used to allow the voltage regulator to adjust,
preventing excessive line voltage reduction. With this
method, a dip appears in the torque curve at half
speed. Overloads and fuses for use with part-winding
starters should be sized for half the motor full load
current and placed in each of the six lines to the motor.
In the first step of part-winding starting, half the motor
winding and a timer are energized. At a predetermined
time interval (usually one second), the second half of
the motor winding is connected in parallel with the first
Star-delta Starters: The motor must be wired for
2 Wire Control
Stop
TR
Start
OL
S
L1
S
L2
TR
F
L3
Fuse
S
S
S
F
F
F
OL OL OL
OL OL OL
T1 T2 T3
T7 T8 T9
Motor
Typical Wiring Diagram
of Part-Winding Starting
Typical Current and Torque Curves
with Part-Winding Starting
for Design “B” Induction Motor
running delta, with enough leads brought out to connect the motor for a star (or wye) start. In the first step
of starting with open transition, the motor is connected
wye and the timer energized. At a predetermined time
interval, the motor is disconnected and reconnected to
the line wired delta. Locked rotor amperage on the star
connection is only 33% of the locked rotor amperage
on delta connections. However, the voltage fluctuation
caused by disconnecting and reconnecting the motor
may be objectionable.
Star-delta starters are available with closed transition.
14
2 Wire Control
1
L1
Stop
Start
3
2
TR
S
S
F
L2
TR
L3
F
F
F
F
T
S
T
S
OL
T
T
S
OL OL OL
T1 T2 T3
T6 T4 T5
Motor
Typical Wiring Diagram of
Star-Delta Starter with
Open-Circuit Transition
Typical Current and Torque Curves
for Design “B” Induction Motor
at the factory. Pilot lights are normally wired in parallel
with the coils whose operation they indicate (see wiring
diagram on page 24).
In the closed transition type, the motor remains connected to the line through resistors during the connection change from star to delta.
Control Transformer: Personnel safety sometimes
dictates low voltage control circuits. To accomplish
this, the control circuit can be wired for connection to a
separate power source, or a control circuit transformer
can be a part of the starter to provide a 115-volt control
circuit voltage. Some control circuit transformers have
enough capacity for a 100-watt work lamp. A fuse in
the secondary circuit provides short circuit protection
for the transformer and control circuit. The wiring
diagram on page 30 shows how to wire a control
transformer into the controls system.
Special Features
Single-Speed Motor Starters
Auxiliary Contacts: Auxiliary contacts, sometimes
called interlocks, are mechanically connected to the
starter so that energizing the starter coil opens the
contacts (N.C.) or closes the contacts (N.O.). Most
starters come with one auxiliary contact. This contact
appears in the holding circuit with three-wire control or
it can control operation of other equipment with twowire control. Additional contacts (1 to 4, depending on
starter) are available factory installed or for field
installation.
Time Delay Contacts or Relays: Reversing a fan
without a time delay imposes a heavy shock load on
the drive. Marley recommends a two-minute time delay
when reversing so that the fan can slow down to
windmilling speed before it actually reverses (see
wiring diagram on page 24).
Push Buttons or Selector Switch on Cover: Push
buttons, pilot lights, or selector switches are available
pre-installed on the cover of NEMA Type 1, 4, 7, 9, and
12 starter enclosures. They are wired into the circuits
The timing head used by some manufacturers employs
15
the starter coil and does not require a coil of its own
(see page 24). Other manufacturers use a timer with
its own coil. On page 24, these timer coils must be in
parallel with the proper starter coil (forward timer coil in
parallel with forward starter coil, etc.). Timers are
available with two different types of contact operation:
when the motor changes to a lower speed without
allowing the motor to adjust to the lower speed. Marley
recommends a 20-second time delay before energizing
a lower speed winding.
Control of Magnetic Starters
Instantaneous operation on energization with time
delay operation on de-energization.
Time delay operation on energization with instantaneous operation on de-energization.
Three-Wire (Push Button) Control
The controls for magnetic starters are either three-wire
or two-wire controls. Three-wire control is manual
control. An operator must push a button to start the
motor.
Additional contacts without time delay are available.
On multi-fan towers, it is sometimes desirable to
prevent more than one fan starting at the same time.
Interlocks in the motor starters and time delay relays
can accomplish this goal. However, some means is
necessary to permit removing a fan from service for
maintenance while the rest of the fans are operating. A
sequence alternator can accomplish the same thing if
only one fan is required at a time and alternating fans is
desirable.
Multi-Speed Starters
Multi-speed motor magnetic starters are available with
the same features listed for single-speed motor starters. The following additional features are also available:
Compelling Relay: A compelling relay connected in a
multi-speed starter allows the motor to start only at low
speed. Any higher speed is available only after a lowspeed start. Pressing any push button except low
speed will not start the motor. This arrangement
insures that the motor will always first move the load at
low speed. The motor can only change from a higher
to a lower speed after the stop button is pressed.
Accelerating Relays: A multi-speed starter equipped
with accelerating relays starts the motor at low speed
and automatically accelerates it through successive
steps until the motor reaches the selected speed. The
operator selects the motor speed by pressing the
proper start button. Definite time intervals must elapse
between each speed change. Individual timing relays
control each interval, and all are adjustable. The motor
can only change from a higher to a lower speed after
the stop button is pressed.
Decelerating Relays: These are similar to accelerating relays except that they prevent immediate reduction
from a higher to a lower speed. Both the driven
machinery and the motors suffer tremendous strains
Starters with three-wire control provide “under voltage
protection” for a motor. When the motor stops because
of a voltage failure, it will not restart until the start
button is pushed.
Separate push buttons select each speed and stop.
Push buttons serve as momentary contact devices.
Once the push button energizes the starter coil, the
circuit bypasses the start button. The circuit may
include any number of push buttons. Start buttons are
in parallel and stop buttons are in series. Standardduty push buttons are available with either normally
open or normally closed contacts. Heavy-duty push
buttons have both normally open and normally closed
contacts. Push buttons are also available with lock-out
devices, built-in lights, and different actuators and
actuator guards. Indicator lights are available with or
without attached transformer. Push buttons are
available in NEMA Type 1, 4, 7, 9, and 12 enclosures.
Selector switches can serve the same function as push
buttons. Since a selector switch is a maintained
contact device, only one can be used to energize a
starter wired for three-wire control. Any number can be
used to de-energize a starter. Hand key or coil operated selector switches are available with two or three
contact positions.
Two-Wire Control
The starter must use three-wire control to provide both
manual and automatic starter control. Where only
automatic control is required, the magnetic starter is
wired for two-wire control. Starters with two-wire
control provide “under voltage release”, which disconnects the motor from the line if the voltage gets too low.
However, the motor automatically goes back on the line
when the voltage comes back up. Limit switches,
pressure switches, temperature switches, and relays
used with two-wire magnetic starter control offer
automatic motor control.
16
Control for Motor Heating
Fan motors that will be idle for long periods should
have some method of heating. Elevating the motor
temperature five or more degrees above ambient
prevents condensation in or on the motor. Two commonly used heating methods are electric space heaters
and low (5% of normal) voltage single-phase heating
using the motor winding. The motor manufacturer
normally installs the space heaters and determines the
transformer size necessary for single-phase heating.
Neither space heaters nor single-phase heating should
be energized while the motor is running. Typical wiring
diagrams appear below.
STOP
L1
START
OL
F
F
L2
R
F
L3
F
F
G
F
F
OL OL OL
Motor
Space Heater
M
Typical Wiring Diagram Showing Connections to Space Heater
STOP
START
CR1
L1
F
L2
R
F
L3
F
F
G
CR1
F
TR
CR1
OL OL OL
CR2
F
TR
CR2
CR2
Heating Transformer
CR2
CR2
OL
Motor
Typical Wiring Diagram Showing Connections for Single Phase Heating
The use of single-phase heating is normally limited to
low voltage (600 volts or less) squirrel cage induction
motors. The wiring diagram shows a time delay relay
to prevent connecting the transformer to the motor
winding until the motor voltages have collapsed. An
available solid state motor winding heater can be
connected to a single-speed full voltage motor starter
without additional control.
17
Motor Overload Protection
The following types of motor overload protection are
used:
motors can always accelerate the load across-the-line
in 13 seconds or less. Refer any questions about fan
starting time to The Marley Cooling Tower Company.
Sensors Built into the Motor
Thermocouples (usually copper-constantan), imbedded
in the coils during assembly, provide a signal to read or
record temperature or sound an alarm.
Resistance temperature detectors imbedded in the
coils provide a signal in a circuit to sound an alarm or
turn off a motor on high temperature. They are normally used only in form wound motors (large HP).
Thermistors, usually with a positive temperature
coefficient, can provide a signal to an auxiliary circuit to
switch a motor starter off. The thermistors, imbedded
in the winding, have a constant resistance until the
critical temperature occurs. The resistance value then
changes by a factor up to one hundred.
Special rate-of-rise temperature switches protect a
motor against overloads and stalled rotor conditions.
Two or more sensors installed in the end turns sense at
least two phases of a three-phase motor and turn off
the motor starter. They automatically reset when the
temperature drops about 15°C. This type of protector
can sense the rapid temperature changes caused by a
stalled rotor.
Thermostats used in motors are usually bimetallic-disc
type attached to the winding end turns. They are
available with either normally open or normally closed
contacts and reset automatically with about a 10°C
temperature drop. They do not normally protect a
motor against the rapid temperature increases caused
by a stalled rotor.
Sensors Built into the Motor Starter
Temperature and current sensitive relays in the motor
starter open the line to the holding coil of the magnetic
starter. A three-phase motor requires three relays, one
in each line. A single-phase motor normally requires
one relay. Properly sized relays trip at not more than
125% of the full load current for motors with a 1.15 or
larger service factor (115% for all other motors).
NEMA classifies these overload relays by time current
characteristics. The class number indicates the time at
which the relay will trip at 600% of the current rating.
Class 10 relays trip in 10 seconds and are normally
used with hermetically sealed motors and other motors
which can endure locked rotor current for only a very
short time. Class 20 relays trip in 20 seconds and are
normally used on cooling tower motors and other
normal motor acceleration applications. Marley fan
In a cooling tower, the fan horsepower increases with
high air density in the winter and decreases with low air
density in the summer. Cooling tower fans are pitched
to draw contract horsepower for summer duty. Fan
horsepower quite often exceeds the motor name plate
horsepower in winter when the air density is high; but
this does not hurt the motor. Allowable motor horsepower is limited by motor temperature, which consists
of ambient plus the temperature rise due to the power
losses in the motor. The temperature rise in winter
(due to increased power losses) is more than offset by
the drop in ambient temperature.
Starter overload capacities vary with ambient (see
Page 19). Overloads can best protect a motor in
summer and winter, without false tripping of the overloads, if they are always at about the same ambient as
the motor. This can be done by installing the starters
outside near the motor. Overloads which are compensated to carry the same horsepowers at high or low
ambient conditions should not be used with cooling
tower fans.
Overloads as Part of the Safety Switch
Dual element fuses in a fusible safety switch give both
short-circuit protection and motor-running overcurrent
protection. Where motors are protected by switches
described above, dual element fuses should be used to
protect the starter and conductors.
Sizing of Motor-Overload Protection
Motor manufacturers select and install Type A overcurrent devices. The proper size for a Type B device
depends on the motor operating horsepower full load
current, the starter enclosure, and the temperature of
the starter relative to the temperature of the motor.
Most overload selection tables apply to motors with a
service factor greater than 1.0. The overload heaters
for 1.0 service factor motors are normally smaller and
their selection appears in a footnote with the table.
Overload selection tables are usually attached to the
inside of the motor starter enclosure. The proper size
for a Type C device depends on the motor operating
horsepower full load current.
The motor full load current appears on the motor name
plate. Currents vary with manufacturer and with motor
design (one-speed, two-speed, one-winding, etc.).
Nominal current values for 60 Hz, 1800 RPM motors
appear in Tables 14 and 15.
18
Variation in Starter Overload Tripping Current with Ambient Temperatures
19
Table 14 - Average Motor Full Load Amps and Minimum Conductor and Conduit Size
(1984 N.E.C.) for 60 Cycle Induction Type A.C. Motor Circuits 200 V & 230 V
Full Load Amps
HP
200 V
230 V
1/2
3/4
1
1 1/2
2
3
5
7 1/2
10
15
20
25
30
40
50
60
75
100
125
150
200
2.3
3.2
4.1
6.0
7.8
11.0
17.5
25.3
32.2
48.3
62.1
78.2
92.0
119.6
149.5
177.1
220.8
285.2
358.8
414
552
2.0
2.8
3.6
5.2
6.8
9.6
15.2
22
28
42
54
68
80
104
130
154
192
248
312
360
480
Wire & Conduit Sizes for
Wire & Conduit Sizes for
Types RUW, T, TW Wire
Types RH, RHW, RUH, THW, THWN, XHHW Wire
200 V
230 V
200 V
230 V
Wire
Conduit
Wire
Conduit
Wire
Conduit
Conduit
Wire
Conduit
Conduit
AWG or
AWG or
AWG or RH, RHW, THWN AWG or RH, RHW, THWN
MGM
MGM
MGM RUH, THW XHHW
MGM RUH, THW XHHW
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
12
1/2
14
1/2
12
1/2
1/2
14
1/2
1/2
10
1/2
10
1/2
10
3/4 *
1/2
10
3/4 *
1/2
8
1/2
8
1/2
8
1 *
1/2
8
1 *
1/2
6
1
6
1
6
1 1/4 *
3/4
8
1 *
1/2
3
1 1/4
4
1
4
1 1/4 *
1
6
1 1/4 *
3/4
2
1 1/4
2
1 1/4
3
1 1/4
1
4
1 1/4 *
1
0
1 1/2
1
1 1/4
2
1 1/4
1 1/4
3
1 1/4
1
00
1 1/2
0
1 1/2
0
2
1 1/4
2
1 1/4
1 1/4
0000
2
000
2
00
2
1 1/2
0
2 *
1 1/4
300
2 1/2
250
2 1/2
0000
2 1/2 *
2
000
2
1 1/2
400
3
300
2 1/2
250
2 1/2
2
0000
2 1/2 *
2
600
3
500
3
400
3
2 1/2
300
2 1/2
2 1/2
900
4
700
3 1/2
600
3 1/2 *
3
500
3
3
2000
1250
4 1/2
900
4
3 1/2
700
3 1/2 *
3 1/2
2000
1250
5 *
4
900
4
3 1/2
Table 15 - Average Motor Full Load Amps and Minimum Conductor and Conduit Size
(1984 N.E.C.) for 60 Cycle Induction Type A.C. Motor Circuits 460 V & 575 V
Full Load Amps
HP
460 V
575 V
1/2
3/4
1
1 1/2
2
3
5
7 1/2
10
15
20
25
30
40
50
60
75
100
125
150
200
1.0
1.4
1.8
2.6
3.4
4.8
7.6
11
14
21
27
34
40
52
65
77
96
124
156
180
240
0.8
1.1
1.4
2.1
2.7
3.9
6.1
9
11
17
22
27
32
41
52
62
77
99
125
144
192
Wire & Conduit Sizes for
Wire & Conduit Sizes for
Types RUW, T, TW Wire
Types RH, RHW, RUH, THW, THWN, XHHW Wire
460 V
575 V
460 V
575 V
Wire
Conduit
Wire
Conduit
Wire
Conduit
Conduit
Wire
Conduit
Conduit
AWG or
AWG or
AWG or RH, RHW, THWN AWG or RH, RHW, THWN
MGM
MGM
MGM RUH, THW XHHW
MGM RUH, THW XHHW
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
14
1/2
14
1/2
14
1/2
1/2
14
1/2
1/2
12
1/2
14
1/2
12
1/2
1/2
14
1/2
1/2
10
1/2
12
1/2
10
3/4 *
1/2
12
1/2
1/2
8
1/2
10
1/2
10
3/4 *
1/2
10
3/4
1/2
6
1
8
1/2
8
1 *
1/2
8
1
1/2
6
1
6
1
6
1 1/4 *
3/4
8
1
1/2
4
1
6
1
6
1 1/4 *
3/4
6
1 1/4
3/4
3
1 1/4
4
1
4
1 1/4 *
1
6
1 1/4
3/4
1
1 1/4
3
1 1/4
3
1 1/4
1
4
1 1/4
1
0
1 1/2
2
1 1/4
2
1 1/4
1 1/4
3
1 1/4
1
000
2
0
1 1/2
0
2 *
1 1/4
2
1 1/4
1 1/4
0000
2
000
2
000
2
1 1/2
0
2
1 1/4
300
2 1/2
0000
2
0000
2 1/2 *
2
000
2
1 1/2
400
3
300
2 1/2
300
2 1/2
2 1/2
0000
2 1/2
2
700
3 1/2
500
3
500
3
3
300
2 1/2
2 1/2
20
Soft Start Motor Controller
Several manufacturers offer “Soft Start Motor Controllers”. These controllers use silicon controlled rectifiers
(SCR’s) to ramp the motor starting voltage (starting at
zero and increasing to full voltage over a period of
time). The starting time is adjustable from one second
up to 24 seconds or more, depending on the manufacturer. The advantage of soft start is the reduced
starting torque and shock on the fan drive.
An energy saving feature in these controllers reduces
the voltage to the motor at partial loads. This reduces
the losses in the motor by reducing the magnetic flux
density. It also improves the power factor. The cost of
these controllers is approximately $30 per horsepower
in a NEMA 12 enclosure.
A soft start controller is usually installed between the
“across-the-line” starter and the motor.
Variable Frequency Drive
The past few years have seen considerable development of variable frequency controls that permit operating standard, three-phase, squirrel cage induction
motors as variable speed motors. These controllers
convert one or three-phase a.c. power to d.c., then reconvert it to three-phase variable voltage and frequency power. They try to maintain constant volts per
cycle so that the motor torque remains constant at all
speeds. Motor cooling becomes less effective at low
speeds, so some applications may require reduced
load torque at lower speeds. However, this limitation
does not apply to fan and pump applications.
inverter are less than with a VSI inverter since the
power supplied is closer to a sine wave.
In addition, the motor losses on a VSI control increase
10% to 20% because the input is a square wave rather
than a sine wave source. The temperature rise in a
motor varies almost directly with the losses. As an
example of these two effects, an 80°C rise 90%
efficient motor would have a 96°C rise and be 88%
efficient when operating on a square wave. Because of
this effect, some motor manufacturers recommend
using a high efficiency 1.15 service factor motor with an
inverter power source.
Diode or SCR bridges convert the a.c. power to d.c.
The drive also controls the voltage by adjusting the
firing point of the SCR’s. Some users have reported
that SCR’s introduce noise back in the line, causing
problems with computers. An isolation transformer
and/or suppression equipment either at the computer
or at the variable frequency drive may be necessary if
this occurs.
Motor starting time and torque and decelerating time
and torque are adjustable with a variable frequency
controller. The cost per horsepower of variable frequency controls decreases as the horsepower capacity
of the control increases. Cost and performance of
variable frequency drives will continue to improve as
development continues and the devices gain popularity. Base unit prices do not include a temperature
controller, start-up engineer, critical speed lockout,
safety disconnect or motor starters to permit alternate
operation direct across-the-line.
Diode bridges, on the other hand, cannot regenerate
power back to the a.c. line (regenerative braking).
Manufacturers who use diode bridges instead of SCR’s
to convert to d.c. usually guarantee that they will not
put noise back to the line. Since the d.c. from a diode
bridge is at constant voltage, it is necessary to add an
SCR or transistor to the output to control the voltage to
some inverters.
The designer must consider several other restrictions
when specifying a variable frequency controller for a
water cooling tower. Splash lubricated gear reduction
units require a minimum operating speed for adequate
lubrication. This minimum input speed varies with the
gear unit design, and is between 440 and 750 RPM on
a Marley Geareducer®. The inverter controls must
prevent motor operation below the minimum speed.
The device that changes d.c. back to variable frequency a.c. is called an inverter. Three basic inverter
designs are common:
(1) Six steps voltage inverter (VSI).
(2) Six steps current inverter (CSI).
(3) Pulse width modulating inverter (PWM). This
inverter uses constant voltage d.c.
Also, some tower components may have a natural
frequency within the range of operating speeds of a
variable frequency motor drive. If the equipment
operates for any significant time at the critical speed, a
catastrophic failure could occur. Therefore, the inverter
controls must prevent operation at or near a critical
frequency. Most variable frequency control manufacturers offer field-installed kits to “lock out” a 4 Hz band
around a critical frequency.
Most variable frequency drives in the 1 to 200 HP
range use voltage source inverters (VSI). Many 1 to 20
HP units are the (PWM) type. The losses at full load in
the power source are about 3% for the VSI type and
5% for the PWM type. Motor losses with a PWM
21
Programmable Controllers
It has always been possible to reduce the cooling effect
on a multi-fan tower by turning off fans or reducing fan
speed with a multi-speed motor. Either an operator
changed speeds manually or automatic controls with
thermostats changed the speed using relays and
timers.
A thermostat normally controlled each speed change
on each motor. The thermostats were all set at different temperatures to prevent changing speed on more
than one fan at a time. By adding timers or a multicircuit timer, it was possible to use one thermostat
(temperature) to increase speed and another thermostat (temperature) to decrease speed of all fans as
required.
Programmable controllers are now available to increase or decrease fan speed; wait for the water
temperature to stabilize; then change another fan
speed. These controls can also prevent motor overheating from excessive cycling. They still require two
thermostats, one to increase fan speed and one to
decrease fan speed. A dead band between the two
temperatures allows operation with no speed change
required. Programmable controllers replace only the
control of the magnetic motor starters, not the magnetic
starters themselves.
The cost of a programmable controller depends on the
number of inputs and outputs required. An input could
be a thermostat or selector switch, for example.
Switching a motor speed would be considered an
output. For example, 4 two-speed motors would
require eight outputs to get eight changes in tower air
rate.
22
Purchasing Information (for Control Equipment)
The customer should specify the following information
when purchasing individual items of control equipment.
6. Timing range desired.
7. Relay type: “Fluid dashpot”, “Pneumatic”,
“Motor drive”, or “Electronic”.
Magnetic Across-the-Line Starter
Push-Button Stations
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Single or multi-speed.
Motor horsepower (each speed).
Line voltage.
Frequency (cycles).
Number of phases. (Number of wires if twophase.)
Full load motor current (at each speed if more
than one speed).
Enclosure type by NEMA type number and size
number.
Desired control type on cover: start-stop
buttons, plain cover, or selector switch marked
“Hand”, “Off”, and “Automatic”.
On multi-speed motor starters, state if “consequent pole” or “separate winding”. State if motor
is “constant torque”, “variable torque”, or “constant horsepower”.
On Multi-speed and single-phase motor starters,
send terminal diagram of motor.
State whether pilot control device is two or
three-wire. Three-wire is for push button
control. If two-wire, describe pilot device. State
voltage if different from line voltage.
State if compelling relay, accelerating relay,
decelerating relay, or extra interlocks are
desired on starter.
State if motor will be reversed. If two-speed
motor, will motor be reversed one-speed or twospeed. If reverse one-speed, which speed.
1.
2.
3.
4.
Number of stations needed.
Marking of each button.
Enclosure type by NEMA number.
State whether contacts are normally-open,
normally-closed, or both. Standard-duty buttons
have normally-closed or normally-open
switches. Heavy-duty buttons are all normallyopen, normally-closed.
Safety Switch
1.
2.
3.
4.
5.
6.
7.
8.
Motor horsepower and full load current.
Line voltage.
Number of phases.
Enclosure type by NEMA number.
State if fuse holders are desired.
State if fuses are to be included (extra).
State if cover is interlocked.
State the position and size of hub or conduit
openings, if not standard.
Float Switch
1.
2.
3.
4.
5.
6.
7.
Timing Relay
1.
2.
3.
4.
Whether a.c. or d.c.
Line voltage.
If a.c., state frequency (cycles).
Contact arrangement desired, (i.e., normallyopen or normally-closed).
5. Enclosure type by NEMA number.
Voltage.
Horsepower rating.
Whether a.c. or d.c.
If a.c., state phases.
Chain or rod operated.
Length of chain or rod.
Enclosure type by NEMA number.
Temperature Switch (Thermostat)
1.
2.
3.
4.
5.
23
Whether a.c. or d.c.
Horsepower rating.
Desired cut-in & cut-out temperatures.
Voltage.
If a.c. state phases.
Wiring Diagram of Three Phase Magnetic Starter
Single Speed Motor with
Reversing with Time Delay and
Push Button Control
Minimum Time Delay
Reversing - 2 Minutes
STOP
R
FWD
R
R
OL
L1
F
CR1
CR1
L2
L3
R R R
REV
F
F F F
CR2
G
F
R
CR2
OL
T1 T2
T3
Fan
Motor
Item
Starter
Push Button
Allen Bradley
Bulletin 505
Bulletin 800T
Cutler Hammer
File A50
File E20
General Electric
CR 309 Form
CR 104P Form
24
Square D
Class 8736
Class 9001
Westinghouse
Class A-211
Type PB2
Wiring Diagram of Three Phase Non-Reversing Starter
Two Speed Consequent Pole Variable Torque Motor with
Time Delay on Deceleration and Push Button Control
Low
A1
Minimum Time Delay
High to Low Speed - 20 Seconds
H
Stop
OL
H
L
L1
CR1
L2
A2
CR1
L3
High
L
L
H
L
L
L
H
LOL
H
H
H
H
HOL
H
A1
A2
T1 T2 T3
T6 T4 T5
X
X
Safe
Run
Fan
Motor
Item
Starter
Push Button
Allen Bradley
Bulletin 520
Bulletin 800T
Cutler Hammer
File A700
File E20
General Electric
CR 309 Form
CR 104P Form
Square D
Class 8810
Class 9001
Westinghouse
Class A-900
Type PB2
L1
L2
L3
L
Note:
If motor is separate winding type, use
same control circuit but change power
circuit to that shown at right.
L
L
LOL
T1 T2 T3
Fan
Motor
25
H
H
H
HOL
T11 T12 T13
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with
Time Delay on Deceleration, Reversing Low Speed with Time Delay
and Push Button Control
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
VIB
SW
A1
Stop
L1
L3
20 Sec
HF
LF
CR3 CR2 CR1
A2
L2
LF
CR1
LR 2 Min TR1
LR
CR3 CR2 CR1
LF LF LF LR LR LR HF HF HF
CR2
HF
HF
2 Min LR
CR3 CR2 CR1
CR3
LF
TR1
HF
HF HF
T3
T1 T2
T6 T4
T5
OL
Fan
Motor
A1
A2
X
Run
X
Safe
L1
L2
L3
LF LF LF LR LR LR HF HF HF
Note:
T3
T1 T2
T11 T12
If motor is separate winding type, use
same control circuit but change power
circuit to that shown at left.
T13
Fan
Motor
Item
Starter
Push Button
Selector
Switch
Allen Bradley
Bulletin 520
Bulletin 800T
Bulletin 800T
Cutler Hammer
File A700
File E20
File E20
General Electric
CR 309 Form
CR 104P Form
CR 104P Form
26
Square D
Class 8810
Class 9001
Class 9001
Westinghouse
Class A-900
Type PB2
Type PB2
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with
Time Delay on Deceleration, Reversing Both Speeds and Push Button Control
A1
Stop
Low
H
CR1
High
L3
F
F
R
R
L
CR1
A2
F
OL
H
L1
L2
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
L
H
R
H
L
L
L
L
H
LOL
H
H
H
C1
R
C2
F
F
H
HOL
R
H
T1 T2 T3
T6 T4 T5
A1
A2
X
Run
C1
C2
X
Safe
X
Fwd
X
Rev
Fan
Motor
Item
Starter
Push Button
Selector
Switch
Allen Bradley
Bulletin 520
Bulletin 800T
Bulletin 800T
Cutler Hammer
File A700
File E20
File E20
General Electric
CR 309 Form
CR 104P Form
CR 104P Form
Square D
Class 8810
Class 9001
Class 9001
Westinghouse
Class A-900
Type PB2
Type PB2
L1
L2
Note:
If motor is separate winding type, use
same control circuit but change power
circuit to that shown at right.
L3
F
L
F
L
F
R
R
R
L
H
H
H
LOL
T1 T2 T3
Fan
Motor
27
HOL
T11 T12 T13
Wiring Diagram of Three Phase Starter
Two Speed Consequent Pole Variable Torque Motor with
Time Delay on Deceleration
Automatic Temperature and Push Button Control
Minimum Time Delay
High to Low Speed - 20 Seconds
A1
Functions
@ 60°F
Vib
Switch
Functions
@ 40°F
H
B1
L1
L
A2
L2
L
L3
B2 Stop
L
L
L
LOL
H
H
H
H
CR1
Low
CR1
H
CR1
HOL
High
L
H
H
H
T1 T2 T3
OL
T6 T4 T5
Fan
Motor
A1
A2
X
Run
B1
B2
X
Safe
X
X
Hand
Item
Allen Bradley
Cutler Hammer General Electric
Square D
Starter
Bulletin 520
File A700
CR 309 Form
Class 8810
Push Button Bulletin 800T
File E20
CR 104P Form
Class 9001
Temperature
See Minneapolis Honeywell, Penn or Barber Coleman
Switch
Off
Auto
Westinghouse
Class A-900
Type PB2
L1
L2
Note:
If motor is separate winding type, use
same control circuit but change power
circuit to that shown at right.
L3
L
L
L
LOL
T1 T2 T3
Fan
Motor
28
H
H
H
HOL
T11 T12 T13
29
Run
X
X
Safe
L3
L2
L1
L3
L2
L1
B1
B2
X
Hand
Fan
Motor
T11 T12
LR LR LR LF LF LF HF HF HF
T3
T1 T2
Off
Auto
X
C1
C2
T13
T5
For
X
A2
A1
X
Rev
VIB
SW
B2
B1
Stop
T1
L
H
Low
LF
HF
CR2
High
CR1
T2
C2
C1
LF
Note:
T1 Functions at 60°F
T2 Functions at 40°F
2 Min
TR1
20 Sec
TR3
2 Min
TR2
Type PB2
Class A-900
Westinghouse
OL
TR1
TR3
HF
CR2
TR2
LR
LF
CR1
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
Item
Allen Bradley
Cutler Hammer General Electric
Square D
Starter
Bulletin 520
File A700
CR 309 Form
Class 8810
Push Button Bulletin 800T
File E20
CR 104P Form
Class 9001
Temperature
See Minneapolis Honeywell, Penn or Barber Coleman
Switch
T6 T4
Fan
Motor
HF HF
T3
T1 T2
LF LF LF LR LR LR HF HF HF
Note: If motor is separate
winding type, use
same control circuit
but change power
circuit to that shown
below.
A1
A2
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with Time Delay on Deceleration
Reversing Low Speed with Time Delay
Automatic Temperature and Push Button Control
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with Time Delay on Deceleration
Reversing Both Speeds with Time Delay Automatic Temperature and Push Button Control
and 120 VAC Control Transformer
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
A1
Vib
Switch
L1
Functions
@ 60°F
Functions
@ 40°F
H
B1
L
A2
L2
L
H
L
L3
F
F
F
R
R
B2 Stop
R
H
CR1
Low
CR1
CR1
High
L
L
L
L
LOL
H
H
H
H
HOL
L
R
C1
C2
H
F
H
H
T1 T2 T3
Fan
Motor
F
R
OL
T6 T4 T5
A1
A2
X
Run
X
Safe
B1
B2
X
X
Hand
Off
C1
C2
X
For
Auto
Item
Allen Bradley
Cutler Hammer General Electric
Square D
Starter
Bulletin 520
File A700
CR 309 Form
Class 8810
Push Button Bulletin 800T
File E20
CR 104P Form
Class 9001
Temperature
See Minneapolis Honeywell, Penn or Barber Coleman
Switch
Westinghouse
Class A-900
Type PB2
L1
L2
L3
R
Note:
If motor is separate winding type, use
same control circuit but change power
circuit to that shown at right.
L
R
L
R
F
F
F
L
H
H
H
LOL
T1 T2 T3
Fan
Motor
30
X
Rev
HOL
T11 T12 T13
31
L3
L2
L1
Fan
Motor
T11 T12
T13
T3
T1 T2
HF HF
LF LF LF LR LR LR HF HF HF
T3
T1 T2
A1
A2
Run
X
Fan
Motor
T4 T6
A2
X
Safe
A1
VIB
SW
C2
C1
Stop
C1
C2
CR2
H
L
X
Hand Auto
X
TM2
TM1
CR2
LF
HF
CR1
CR2
CR2
Low
HF
High
2 Min
LR
Westinghouse
Class A-900
Type PB2
Type PB2
Program
Timer
CR2
TM
LR
TR1
CR1
LF
HF
Square D
Class 8810
Class 9001
Class 9001
OL
2 Min
TR1
20 Sec
HF
LF
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
Item
Allen Bradley
Cutler Hammer General Electric
Starter
Bulletin 520
File A700
CR 309 Form
Push Button Bulletin 800T
File E20
CR 104P Form
Selector
Bulletin 800T
File E20
CR 104P Form
Switch
Program
See Zenith or Automatic Timing & Controls
Timer
T5
LF LF LF LR LR LR HF HF HF
Note: If motor is separate winding
type, use same control
circuit but change power
circuit to that shown below.
L3
L2
L1
Suggested Automatic Reversing Cycle
1. 40 Minutes Forward
2. 20 Minutes Reverse
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with Time Delay on Deceleration
Reversing Low Speed with Time Delay, Automatic Temperature and Push Button Control
32
Time
X
Fwd
X
Run
X
X
Off
X
Rev
X
Safe
L3
L2
L1
L3
L2
L1
B1
B2
X
Hand
Off
Auto
X
T3
T1 T2
Fan
Motor
T6 T4
Fan
Motor
T2 T3
T11 T12
T13
LR LR LR LF LF LF HF HF HF
T1
HF HF
T5
LR LR LR LF LF LF HF HF HF
Note: If motor is separate winding
type, use same control
circuit but change power
circuit to that shown below.
D1
D2
C1
C2
A1
A2
VIB
SW B1
B2
Functions
@ 32°F
Stop
CR2
CR1
D2
D1
L
H
HF
LF
CR2
CR1
Functions
@ 40°F
C2
C1
CR2
High CR1
CR1
CR2
Low
LF
2 Min
TM2
TR1
Functions 20 Sec
@ 60°F
HF
TM1
OL
CR2
CR1
TR1
HF
LF
TM
Westinghouse
Class A-900
Type PB2
2 Min
LR
LR
Minimum Time Delay
1. High to Low Speed - 20 Seconds
2. Reversing - 2 Minutes
Item
Allen Bradley
Cutler Hammer General Electric
Square D
Starter
Bulletin 520
File A700
CR 309 Form
Class 8810
Push Button Bulletin 800T
File E20
CR 104P Form
Class 9001
Selector
See Minneapolis Honeywell, Penn, or Barber Coleman
Switch
Program
See Zenith or Automatic Timing & Controls
Timer
A2
A1
Suggested Automatic Reversing Cycle
1. 40 Minutes Forward
2. 20 Minutes Reverse
Wiring Diagram of Three Phase Magnetic Starter
Two Speed Consequent Pole Variable Torque Motor with Time Delay on Deceleration
Reversing Low Speed with Time Delay, Reversing Low Speed with Program Timer
Automatic Temperature and Push Button Control
Cooling Technologies
7401 W 129 Street • Overland Park, KS 66213 • 913 664 7400
www.marleyct.com • email: info@marleyct.com
In the interest of technological progress, all products are
subject to design and/or material change without notice.
©2001 Marley Cooling Technologies
Printed in USA