Onan OT II User manual

Orton
Operators
Manual
©TDD
Switch
Utility-to-GenSet
Automatic Control
962-0107
Begin Spec E
7/82
Printed in U.S.A.

Safety Precautions
This manual includes the following symbols to indi¬
cate potentially dangerous conditions to the operator
or equipment. Read the manual carefully and know
when these conditions exist. Then take the necessary
steps to protect personnel and the equipment.
This symbol is used throughout the
text to warn of possible injury or
This symbol is used to warn of pos-
^sib/e equipment damage.
The OT transfer switch has components with high
voltages which present serious shock hazards. For
this reason, read the following suggestions.
Keep the transfer switch cabinet closed and locked.
Make sure only authorized personnel have the
cabinet and operational keys.
Due to high voltages of components within the
cabinet which present a serious shock hazard, always
have an electrician or authorized service representa¬
tive perform any service or adjustments to the auto¬
matic transfer switch. If the cabinet must be opened
forany reason: 1) always move the operation selector
switch on the generator set or Stop/Auto/Hand
Crank switch on the automatic transfer switch,
whichever applies, to STOP; 2) disconnect the start¬
ing batteries of the generator set; and 3) remove AC
power to the automatic transfer switch. If the instruc¬
tions require otherwise, use extreme caution due to
the danger of shock hazard.
Use rubber insulative mats placed on dry wood plat¬
forms over floors which are metal or concrete when
working on any electrical equipment. Do not wear
damp clothing (particularly wet shoes) or allow skin
surfaces to be damp when handling any electrical
equipment.
Jewelry is a good conductor of electricity and should
be removed when working on the electrical equip¬
ment.
^JWARNIN^j
death.
Do not work on this equipment when mentally or
physically fatigued.
OT2-UG-1

Onon
Supplement 962-1013
Date: 6-85
Insert with -
Title: OT II Operator’s Manual
Number 962-0107
This supplement applies to the 40 through 1000 ampere, Spec Eand later OT II transfer switch. The two to three wire
converter is available for converting the two wire start transfer switch for use with a three wire start generator set. The
converter includes a Start Disconnect relay, Overcrank relay, and may include a Preheat Time delay depending on the
options selected.
INSTALLATION SECTION
2 to 3 Wire Converter
The converter mounts on the left inside cabinet wall
directly below terminal block TB2 and use the same
remote TB10 connections for three-wire starting as
shown in the Operator’s Manual. Reference Figure 9.
CHECKOUT PROCEDURES
Overcrank Relay and Voltage Sensor Adjustments
(Three-wire starting only)
1. Locate the overcrank relay on the converter as
shown in Figure 9. It has a range of 0 to at least 180
seconds. The maximum time delay occurs between
the F and 0. At 0, there is no time delay. Turning the
knob to A equals about 30 to 40 seconds. See listing
below for times and settings.
If the converter also includes a preheat relay, double the time
setting. For example, set the knob to 60 seconds to obtain a
30-second overcrank relay time.
A — 30 to 40 seconds
B — 60 to 90 seconds
C — 90 to 150 seconds
D —150 to 210 seconds
E — 210 to 260 seconds
F — 240 to 360 seconds
The small button next to the adjustment knob bypasses the
delay function. The button should not be used for normal
operation.
2. Locate the Voltage Sensor (Start Disconnect) on the
converter as shown in Figure 9. It senses generator
output and at a predetermined voltage value, ener¬
gizes to open the start circuit (after the generator set
is running). Refer to following table for correct set¬
ting of sensor.
TB2
VOLTAGE SENSOR
RELAY (START DISCONNECT)
PREHEAT
RELAY
(OPTIONAL)
OVERCRANK
RELAY
2 TO 3 WIRE
CONVERTER
MOUNTING BASE
ES-1543
ACAUTION
Do not set voltage sensor above
rating of transfer switch or sen¬
sor will not operate. Improper adjustment can
result in abnormal operation of transfer switch.
FIGURE 9. LOCATION OF 2 to 3 WIRE CONVERTER,
OVERCRANK RELAY AND OPTIONAL PREHEAT
TIME DELAY

APPROXIMATE VOLTAGE SENSOR PICKUP SETTINGS
120-VOLT
208-240 VOLT
! 480-VOLT
600-VOLT
DIAL SETTING
MODEL j MODEL
MODEL
MODEL
1 93 T 183 390 488

Contents
TITLE
SAFETY PRECAUTIONS .
INTRODUCTION .
Operator’s Manual .
Transfer Switch Application .
Automatic Transfer Switches ...
Model Identification .
INSTALLATION ..
Location .
Mounting .
Wiring .
Cleaning of Cabinet .
Checking Procedures .
DESCRIPTION .
Cabinet .
Transfer Switch .
Electronic Control .
Relay Control .
OPERATION .
Automatic Operation .
Manual Operation .
Generator Set Exercise .
Standby System Test . ; .
Starting Circuit Reset .
TROUBLESHOOTING .
Power Outage Occurs But Generator Set Does Not Start .
Generator Set Starts During Normal Power Service .
Generator Set Does Not Exercise (If Equipped With Exerciser) .
Generator Set Starts But Does Not Assume Load .
No Transfer Of Load To Normal Power From Generator Set .
Generator Set Continues To Run After Retransfer Of Load To Normal Power
Battery Charger Fails To Charge (If Equipped) .
Battery Loses Water .
Battery Loses Charge .
PARTS AND SERVICE INFORMATION
PAGE
Inside Cover
. 2
. 2
. 2
. 2
. 2
. 3
. 3
. 3
. 4
. 7
. 7
. 13
. 13
. 14
.. 14
. 18
. 19
. 19
. 19
. 19
. 20
. 20
. 21
. 21
. 21
. 21
. 22
. 22
. 22
. 22
. 22
. 22
. 23
warningJ
INCORRECT SERVICE OR REPLACEMENT OF PARTS MIGHT RESULT IN
SEVERE PERSONAL INJURY AND/OR EQUIPMENT DAMAGE. SERVICE
PERSONNEL MUST BE QUALIFIED TO PERFORM ELECTRICAL AND/OR
MECHANICAL SERVICE.
1

Introduction
OPERATORS MANUAL
Thjs operators’ manual provides information neces¬
sary for operation of the Onan OT transfer switch.
The manual includes installation, description, and
operation chapters. A troubleshooting guide is also
included. Operators should become familiar with this
manual, especially the operation procedures which
apply to their automatic transfer switch.
TRANSFER SWITCH APPLICATION
Transfer switches are an essential part of a building’s
standby or emergency power system. The Normal
powersource, commonly the utility line, is backed up
by an Emergency power source, often an electric
generating set. A transfer switch supplies the electri¬
cal load with power from one of these two power
sources. The load being served is connected to the
common of the transfer switch as shown. Under nor¬
mal conditions, the load is supplied with power from
the Normal source (as illustrated). Should the Normal
power source be interrupted, the load is transferred
to the Emergency powersource. When Normal power
returns, the load is retransferred to the Normal power
source. The transfer and retransfer of the load are the
two most basic functions of a transfer switch.
NORMAL
EMERGENCY
SC-1101
FIGURE 1. LOAD TRANSFER SWITCH
(TYPICAL FUNCTION)
AUTOMATIC TRANSFER SWII HES
Automatic transfer switches, capable ov Tomatic
operation without operator involvement. : orm the
following basic functions:
1. Sense the interruption of the Nc .i power
source.
2. Send a start signal to the general- ::et (Emer¬
gency power source).
3. Transfer the load to the Emergenc . wer source.
4. Sense the return of the Normal p : er source.
5. Retransfer the load to the Normai power source.
6. Send a stop signal to the generator set.
MODEL IDENTIFICATION
Identify your model by referring to the Model and
Specification number as shown on the nameplate.
Electrical characteristics are shown on the lower por¬
tion of the nameplate. It is located inside the cabinet
door on the control box cover.
If it is necessary to contact a dealer or the factory
regarding the transfer switch, always give the com¬
plete Model, Spec, and Serial number as listed on the
nameplate. Also give the number(s) of any options
that may be listed on a label below the nameplate.
This information is necessary to properly identify
your unit among the many types manufactured.
A typical model number with explanation is given
below.
OT B C A 260 - 4X U / 31 01 E
TTTTT TT TTT
12345 67 89 10
1. Basic mode! series.
OT indicates OT II transfer switch series
2. Number of switched conductor poles.
B-indicates 3-pole.
3. Basic control group.
C-indicates utility to standby generator.
4. Enclosure type.
A-indicates general purpose NEMA T
5. Ampere rating.
6. Voltage code and frequency.
4X or 54X (50 Hz) = 277/480. 3-phase. 4-wire.
7. Agency Certification.
U-Underwriters’ Laboratories, Inc.
8. Control option group number.
9. Meter option group number.
10. S p ecification letter: advances with production modification.
2

Installation
LOCATION
Locating the transfer switch in the existing electrical
circuit varies with application and type of entrance
switch. There must be a switch and fuses in the com¬
mercial power line before the transfer switch. A typi¬
cal installation is shown in Figure 2.
Choose a vibration-free mounting surface. Avoid hot,
moist, or dusty locations.
TABLE 1. APPROXIMATE CABINET DIMENSIONS
Depth W/Door— j
Switch
Amp
Rating
Height
(H)
Width
(W)
Closed
(D)
Open
°o) ...
40,
30.5-in
23.0-in
13.5-in
32.75-in
70,
100
(775mm)
(584mm)
(343mm)
(832mm)
150,
63.0-in
30.0-in
21.6-in
44.2-in
260
(1600mm)
(762mm)
(549mm)
(1122mm)
400
78.0-in
(1981mm)
30.0-in
(762mm)
22.6-in
(574mm)
46.2-in
(1173mm)
600,
84.0-in
36.0-in
22.6-in
51.7-in
800,
1,000
(2134mm)
(914mm)
(574mm)
(1313mm)
MOUNTING
Wall Mount, 40-100 Ampere
1. Install two mounting bolts in the wall for the bot¬
tom cabinet mounting keyholes.
2. With the shipping box standing so the cabinet is
upright, carefully remove the top and sides of the
box.
3. Raise cabinet and mount on the two mounting
bolts in the wall.
I warning | Have sufficient manpower for
—I lifting and mounting cabinet to
prevent serious personal injury .
4. Tighten two bottom mounting bolts.
5. Install two top mounting bolts and tighten.
WIRES FROM
EMERGENCY SIDE
OF TRANSFER
SWITCH
REMOTE CONTROL
WIRES
LINE WIRES
FROM
FUSED SWITCH
BOX AND METER
LOAD
WIRES
AUTOMATIC TRANSFER
SWITCH
GENERATOR SET
CONTROL BOX
FIGURE 2. TYPICAL WALL MOUNT INSTALLATION
3

Floor Mount, 150-1000 Ampere
1. With the shipping box standing so the cabinet is
upright, carefully remove the top and sides of the
box.
2. Connect a hoist or similar lift to the two lifting
eyebolts on the cabinet top.
Warning 1 Do no * attempt *° manually
because of the danger of
serious personal injury.
3. Carefully raise the cabinet and move it to its
installation location. Mounting bolts are usually
placed in concrete when floor is poured. Bolts
should protrude about one inch (25 mm) from
floor. Secure the cabinet to the floor.
WIRING
Wiring must be performed by qualified personnel
only.
If using rigid conduit between the generator set and
the OT transfer switch, install at least 2 feet (610 mm)
of flexible conduit between the rigid conduit and
generator set to absorb vibration. Run control circuit
wiring in separate conduit from the AC wiring, other¬
wise induced currents could cause operational prob¬
lems within the OT. When facing the front of the
cabinet, knockouts can be made through the top,
bottom, or right side of the cabinet.
Use extreme care to keep drill chips
and fillings out of the relays, con-
tacts, and other parts of the automatic transfer switch
when mounting or connecting conduit Also, screw¬
drivers should be used carefully to prevent damage to
the resistors, coils, and contacts.
Perform wiring in the following sequence:
1. Test operation of the generator set from its own
controls.
2. Stop the generator set and remove the negative
lead from the cranking battery to prevent starting.
warning ) Failure to prevent the generator
-J set from starting before wiring
procedures are performed presents a shock
hazard and might cause serious personal injury
or death.
3. Connect wires of sufficient size to carry rated
current from the line, load, and generator set
directly to the transfer switch terminals which are
marked A,B, and C (A and B on single-phase
switches). Table 2 gives the type and maximum
wire size the transfer switch will accept. Figure 3
shows transfer switch connections.
TABLE 2. TERMINAL LUG CAPACITY
For Copper or Aluminum Conductors
Switch
Amp Rating
Number of
Conductors
Size
of''
Range
jctors
40
1
#0 A
#14 AWG
70
1 #0 AV
#14 AWG
100
1
#0 AW- :
#14 A WG
' 150
1 #6 AWC
350 MCM
260
1
#4 AV 500 iVCM
400
1
350 M
1000 VICM
600
2
#2 AV.
j 600 MCM
800
4
#4 A V.
10 600 MCM
1000
4
#4 A i
to 600 MCM
For transfer switches with an AC am meter, the gener¬
ator load wires must passthrough a transformerthree
times for 40-ampere OT, twice (two primary turns) for
a 70-and 100-ampere OT, once (one primary turn) for
any 150- through 1000-ampere OT. See Figure 4.
4. N e u t r a l bar with lugs is standard on switches
supplied with cabinet. See Table 2 for wire sizes.
OT transfer switches of 150 to 1000 ampere size are
factory assembled with the load terminal lugs at the
top. The load terminal lugs may be moved for a bot¬
tom connection using this procedure:
A. Remove switch covers, and load cover on
front connect units. See Figure 5. On units in
the 600 and 1000 ampere range, the end
assemblies on each end of the actuator rod
must be removed to facilitate removal of the
switch cover.
B. Remove nuts and lockwashers from jumper
strap at center of switch (leave bolts in place).
See Figure 5.
C. Remove screw, lockwasher and flatwasher
securing the standoff insulator to the mount¬
ing base.
D. Reverse position of load strap and replace
hardware removed in Step B. Be sure electri¬
cal joint compound is applied before assembly.
E. Secure standoff insulator at bottom of switch
with hardware removed in Step C.
F. Torque screws and nuts to values shown in
Figure 5.
G. Replace load cover and swiic ' covers.
H. Replace end assemblies on a jator rod and
torque screws to value showr 300 and 1000
ampere units only).
4

EMERGENCY POWER
SOURCE
40/70/100 AMPERE 150-1000 AMPERE
FIGURE 3. TRANSFER SWITCH WIRE CONNECTIONS
40-AMPERE OT (THREE TURNS) 70-100 AMPERE OT (TWO TURNS) 150 THROUGH 1000 AMPERE OT (ONE TURN)
LOAD WIRE LOAD WIRE
LOAD WIRE FROM GEN FROM GEN
FROM GEN
ES-1094
FIGURE 4. CURRENT TRANSFORMER WIRING
5

FIGURE 5. TRANSFER SWITCH LOAD TERMINALS (SIDE VIEW)
150-1000 AMPERE
6

Control Circuit Connections
1. A r ea Protection or Remote Test Switch (if used):
A. To add area protection equipment or a remote
test transfer switch, first remove the jumper
between terminals 7 and 8 of TB1. Figure 6
shows the terminal block location.
B. Connect the two leads from the normally
closed circuit of the area protection equip¬
ment or single-pole, single-throw remote test
switch to terminals TB1-7 and -8. Use number
16 wire for distances up to 800 feet or 244
metres (maximum resistance of 4 ohms per
line).
TERMINAL
FIGURE 6. CONTROL TERMINAL BLOCKS
2. A u x i liary Contacts (if used): Auxiliary contacts
are located on the Normal and Emergency sides
of the transfer switch for external alarm or control
circuitry. Connections for auxiliary contacts can
be made on terminal block TB1 terminals 10
through 15. The contacts have ratings of 10
amperes at 480 VAC. Listed below are open and
closed positions of auxiliary contacts with
transfer switch in neutral position. Moving the
transfer switch to Normal or Emergency only
affects the corresponding auxiliary contacts.
NORMAL
AUXILIARY
CONTACT
TB1-10 — N/O
TB1-11 — N/C
TB1-12 — COM
EMERGENCY
AUXILIARY
CONTACT
TB1-13 — N/O
TB1-14 — N/C
TB1-15 — COM
3. G e n e r ator Failure Contact (Optional for Three-
Wire Start Only): Three-wire starting for Onan
air-cooled generator sets has as an option a
normally-open set of contacts for an external sig¬
nal of a generator failure condition (overcrank).
Connect the remote signal device to terminals
TB10-7 and -8 using number 16 wire for distances
up to 800 feet or 244 metres (maximum of 4 ohms
per line). The contacts have ratings of 10 amperes
at 240 VAC.
4. Remote Start-Stop Connections: Use number 16
wire for up to 100 feet or 30 metres with a maxi¬
mum of 0.5 ohm per line.
A. Two-Wire Starting: Two-wire starting for
Onan water-cooled generator sets uses the
three terminals B+, GND (ground) and
REMOTE of terminal block TB1.
B. Three-Wire Starting: Three-wire starting for
Onan air-cooled generator sets uses the four
terminals, 1 (GND or ground), 2,3, and 4 (B+)
of terminal block TB10 which should connect
to respective terminals of the generator set.
5. Preheat Time Delay (Optional for Three-Wire
Starting Only): In addition to remote start-stop
wiring, the preheat time delay allows for a diesel
engine preheat period. To connect, first remove
the jumper from between terminals TB10-5 and
-6. Then connect a wire from TB10-5 (H) in the
cabinet to terminal H in the generator set control.
When preheat circuit is used, remove jumper between terminal “3”
and “H” in the engine control.
CLEANING OF CABINET
After mounting and wiring of cabinet are completed,
clean the interior with a vacuum cleaner to remove
any chips, filings, or dirt from the cabinet interior and
components.
CHECKOUT PROCEDURES
After the generator set and automatic transfer switch
are properly installed, check the various automatic
transfer switch functions. Follow the appropriate
checkout procedure for the automatic transfer
switch, depending on whether it has a solid-state or
relay control.
Exerciser Clock Settings (if Equipped)
1. Check exerciser. It normally has a factory pro¬
gram for one-half hour exercise once per week
(12:00 to 12:30 p.m. on Saturdays). If you want
other times, proceed to Step 2. If these times are
satisfactory, proceed to Step 3.
2. To change exerciser program:
A. On the large dial, install a trip pin (left-hand
thread) in the inside row of holes for the time
of day you want the generator set to start. See
Figure 7.
B. On the large dial, install a trip pin (left-hand
thread) in the outside row of holes for the time
you want to stop the generator set exercise
period.
Onan recommends settings which will operate the gen¬
erator set for at least 30 minutes each week. Exercising
for one long period is better than several short periods.
7

3. Set exerciser for correct day and hour.
PROGRAMMED
TRANSITION
TIME DELAY
A. Rotate the large dial clockwise until the cor¬
rect time of day aligns with the pointer.
B. Turn the small spoked wheel counterclock¬
wise until the correct day aligns with the
pointer.
Sixteen trip pins are supplied. Store any unused pins on
the time pointer bracket.
C. Install a trip pin (left-hand thread) into the
small spoked wheel for each day no exercise
is desired.
TURN LARGE DIAL
CLOCKWISE ONLY
TURN SPOKED WHEEL
COUNTERCLOCKWISE
EXERCISE CLOCK SET TO
START GENERATOR SET
AT 9 A.M. EACH FRIDAY
AND STOP IT AT 10 A.M.
NOTE: Trip pins are left-hand thread.
SC-1138
FIGURE 7. TYPICAL SETTING OF EXERCISER
Programmed Transition (if equipped)
1. Locate the programmed transition time delay on
the left inside wall of the cabinet (Figure 8). It
normal ly has factory settings fora few seconds. If
the setting is satisfactory, proceed to next check.
Otherwise, proceed to Step 2.
2. The programmed transition has either a time
range of 0.5 to 5 seconds, 1.5 to 15 seconds, or 5
to 50 seconds (three timers are available). Turn
the knob clockwise to increase delay, counter¬
clockwise to decrease time delay. Increments are
marked on the knob.
SC-1139
FIGURE 8. LOCATION OF PROGRAMMED
TRANSITION TIME DELAY
Overcrank Relay and Optional Generator
Failure Contact (Three-Wire Starting Only)
1. Locate the overcrank relay on the three-wire con¬
trol, as shown in Figure 9. It has a range of 0.6 to
60 seconds unless the three-wire control has the
optional relay with the generator failure contact.
Then the time range is from 6 to 60 seconds.
FIGURE 9. LOCATION OF OVERCRANK RELAY AND
OPTIONAL PREHEAT TIME DELAY
2. The time delay has settings from 0 to 100 pe ant.
A 100 percent setting gives a 60 second delay, 50
percent gives 30 seconds, etc. Turn the knob
clockwise to increase the percentage of seconds,
counterclockwise to decrease the percentage.
8

Preheat Time Delay (Option for
Three-Wire Starting Only)
1. Locate the preheat time delay, as shown in Figure
9. It has a time range of 0.6 to 60 seconds.
2. The time delay has settings from Oto 100 percent.
A 100 percent setting gives a 60 second delay, 50
percent gives 30 seconds, etc. If you want a dif¬
ferent time other than the factory setting, turn the
knob clockwise to increase the percentage of
seconds, counterclockwise to decrease the
percentage.
Relay Control Start and Retransfer
Time Delay Settings (if equipped)
1. On the rear of the cabinet door, remove the con¬
trol cover to expose the control components. See
Figure 10.
2. Note the setting on the retransfer ti me delay i n the
upper left corner of the control. It is adjustable
from 3to 30minutes. Onan recommends a setting
of 10 to 15 minutes. To change setting, simply
turn knob to desired time.
START
TIME
DELAY
SC-1161
3. Note the setting of the start time delay in the
upper right corner of the control. It is adjustable
from 1.5 to 15 seconds. Onan recommends a set¬
ting of 1 to 3 seconds. To change setting, turn
knob to desired time.
4. Replace the control cover with the four screws.
Check Switch Positions
1. Exerciser (if equipped). Move the switch on the
exerciser to With Load or Without Load, depend¬
ing on whether you want the generator set to
exercise with or without load (with load selection
results in load transfer during exercise period).
2. Transfer Switch Disconnect Switch. Move the
disconnect switch to the up position for auto¬
matic operation. Close cabinet door when finished.
3. Operation Selector Switch. For a water-cooled
Onan generator set with two-wire starting, move
the operation selector switch on the generator set
control panel to Stop. For an air-cooled Onan
generator set with three-wire starting, move the
keyed Stop/Auto/Hand Crank switch on the OT
cabinet to Stop.
4. Test/Normal/Retransfer Switch. Move the key-
operated test switch on the OT cabinet to Normal.
Connect AC Line
If the transfer switch main contacts are not closed to
the Normal power source side, manually close the
transfer switch to the Normal side. Then connect AC
line power to the automatic transfer switch. The lamp
on the cabinet front should light.
Connect the Battery
warning \ High voltages within the cabinet and
rear side of cabinet door present a
shock hazard which might cause serious personal
injury or death. Use care when opening cabinet door.
Connect the battery and, if equipped with a battery
charger, note charging current by opening cabinet
door and observing ammeter on battery charger.
FIGURE 10. RELAY CONTROL TIME DELAYS
9

Test Overcrank Function,
Three-Wire Starting
A. Disconnect positive start lead from the start
solenoid or starter.
B. Move the Stop/Auto/Hand Crank switch to
Auto.
C. Move Test/Normal/Retransfer switch to Test.
Overcrank lamp on automatic transfer switch
should light at end of crank period (usually
factory set at 60 seconds).
D. Move Test/Normal/Retransfer switch to
Normal.
E. Move the Stop/Auto/Hand Crank switch to
Stop and push the Overcrank button (over¬
crank lamp should go out).
F. Reconnect positive lead to starter or start
solenoid.
G. Move the Stop/Auto/Hand Crank switch to
Auto.
Starting Test
1. Two-wire starting.
A. Move selector switch on engine control to
Run. Generator set should start and run.
B. Move selector switch to Remote. Generator
set should stop.
2. Three-wire starting.
A. Move the Stop/Auto/Hand Crank switch on
automatic transfer switch to Hand Crank.
B. Push start button on generator set control.
Generator set should start and run.
C. Move the Stop/Auto/Hand/Crank switch from
Hand Crank to Stop. Generator set should
stop.
D. Move the Stop/Auto/Hand Crank switch to
Auto. Generator set should not start.
Test Transfer With Load
1. If the OT has the optional exerciser, move the
With Load/Without Load selector switch to With
Load.
2. Move the Test/Normai/Retransfer switch to Test.
Generator set should start after time delay (the
load will be transferred to the generator), and
light the red Emergency lamp on the cabinet
door.
3. Check operation of the AC meters (if equipped)
on the cabinet door.
4. Move the Test/Normal/Retransfer switch to Nor¬
mal. The transfer switch should retransfer load to
the Normal power source and stop the generator
set after any time delays. The Normal lamp
should light.
ELECTRONIC CONTROL SETTINGS
Time Delay/Undervoltage/Overvoltage/
Frequency
The adjustments on the electronic modules are fac¬
tory set and normally do not require field adjustment.
If desired, the Pickup, Dropout and Time Delay set-
tings may be adjusted to other than factory settings
as outlined below. However, the calibration (Cal)
adjustments should be changed only if the nominal
voltage is significantly different than the nameplate
rating, or when installing a replacement sensor
module.
I Haphazard setting of the module
—- l calibration (Cal) adjustments may
result in abnormal operation of the transfer switch.
Complete all installation procedures before any
adjustments are made. All adjustments are made with
a screwdriver through openings in the module panels
by turning a potentiometer (see Figures 12 and 13).
A separate voltage sensor is used for each power
source. They are located one on each side of the time
delay module (Figure 11).
Place the Motor Disconnect Switch (Figure 3) in the
down position when making adjustments. Return
switch to up position after adjustments are
completed.
! warning k High voltages are present within the
control cabinet which might cause
serious personal injury or death. Proceed with care!
FIGURE 11. CONTROL PANEL LAMPS AND MODULES
10

Time Delay Module: The time delay module controls
the following functions:
• Start time delay
• Stop time delay
• Transfer time delay
• Retransfer time delay
If other than factory setting is desired, align the slot
on the potentiometer to the desired markings on the
module panel. See Figure 12. Range of adjustments
and factory settings are as follows:
DELAY
ADJUSTMENT FACTORY
RANGE SETTING
Start
Transfer
Retransfer
Stop
0-6 seconds
0-120 seconds
0-32 minutes
0-8 minutes
2 seconds
2 seconds
15 minutes
5 minutes
Time Delay Module
Start Stop Retranatar Transfer
SC-1269
FIGURE 12. TIME DELAY MODULE
Undervoltage Sensor: The standard voltage sensor
modules monitor the Normal and Emergency power
source foran undervoltage condition. The undervolt¬
age rangeof adjustment is shown below. If otherthan
factory setting is desired, align the slot on the poten¬
tiometer to the desired markings on the module
panel.
ADJUSTMENT FACTORY
FUNCTION RANGE SETTING
Dropout 75% to 98% 85%
Pickup 85% to 100% 95%
1
Under Voltage
i % jgo
—
Voltage
Sensor !
EARLY VERSION
If necessary, the undervoltage sensor for either the
Normal or Emergency sources may be calibrated as
follows (see Figure 11 for location):
1. Ensure that nominal voltage is present on all
phases of the source being calibrated (Normal or
Emergency). On voltage sensors with the fre¬
quency sensing option, the source frequency
must be within the limits set by the Frequency
Pickup Band potentiometer.
2. Turn the Undervoltage Pickup and Dropout
potentiometers on the voltage sensor fully
clockwise.
3. Turn the Undervoltage calibration (Cal) potenti¬
ometer fully clockwise. The Source OK lamp cor¬
responding to source sensor being calibrated
should be on (Source One OK-Normal source,
Source 2 OK-Emergency source). If the Source
OK lamp fails to come on, and the voltage sensor
has an overvoltage sensing option, turn overvolt¬
age Limit and Cal potentiometers fully clock¬
wise.
4. Turn the Cal potentiometer counterclockwise
until the Source OK lamp turns off.
5. Slowly turn the Cal potentiometer until the
Source OK lamp just turns on again.
6. The Undervoltage sensor is now calibrated. If the
Overvoltage sensor was adjusted in Step 3, then
recalibrate it by using the Overvoltage Sensor
calibration procedure.
After calibration, reset the Pickup and Dropout
potentiometers to the factory settings or to desired
setting.
Overvoltage Sensor: The optional overvoltage sensor
detects when the source voltage has exceeded the
overvoltage limit.
If other than factory setting is desired, align the slot
on the potentiometer to the desired markings on the
module panel. See Figure 13. Range of adjustments
and factory settings are shown below.
ADJUSTMENT FACTORY
FUNCTION RANGE SETTING
Limit 105 to 135% 110%
Time Delay 0 to 2 minutes 5 seconds
—
UNDERVOLTAGE
a o IK
FREQUENCY
; S:S
OVERVOLTAGE
O -0-
L*-STANDARD- ►
l< OPTIONAL-^
—OPTIONAL- ►
LATER VERSION
SC-1283
FIGURE 13. VOLTAGE/FREQUENCY SENSOR MODULE
11

The overvoltage pickup point is fixed at 5 percent
below the Limit setting. The adjustable dropout Time
Delay overrides momentary overshoots in voltage.
If necessary, the Overvoltage sensor may be cali¬
brated as follows:
It the Undervoltage sensor has not been calibrated, do so before
proceeding.
1. Ensure that nominal voltage is present on all
phases of the source being calibrated (Normal or
Emergency). On voltage sensors with the fre¬
quency sensing option, the source frequency
must be wiothin the limits set by the Frequency
Pickup Band potentiometer.
2. Turn the overvoltage Limit and Time Delay poten¬
tiometers fully counterclockwise.
3. Turn the Overvoltage Cal potentiometer fully
clockwise. The Source OK lamp for the selected
source should light (Figure 11).
4. Turn the Cal potentiometer counterclockwise
until the Source OK lamp turns off.
5. Slowly turn the Cal potentiometer clockwise until
the Source OK lamp just turns on again.
After calibration, reset the Overvoltage Limit and
Time Delay potentiometers to the desired values.
Frequency Sensor: The optional frequency sensor
detects when the source frequency is ■ f h i n an
acceptable band. This band is centered out the
nominal system frequency (50 or 60 hertz
If other than factory setting is desired, all: :he slot
on the potentiometer to the desired mark on the
module panel. See Figure 13. Range of a otments
and factory settings are shown below.
ADJUSTMENT F TORY
FUNCTION RANGE "TING
Pickup Band ±4 to ±20% ±10%
Time Delay Oto 15 Seconds Seconds
The dropout bandwidth is always 2.5% wider (on
each end) than the pickup bandwidth.
The adjustable dropout Time Delay allows the con¬
trol to ignore momentary dips or rises in frequency.
12

Description
Onan automatic transfer switches basically control
transfer of the load to either Normal power source or
to Emergency power source (generator set) without
operator involvement. Throughout this manual, fre¬
quent references are made to two-wire and three-
wire start-stop functions of generator sets. Onan
water-cooled generator sets have two-wire start con¬
trols and the air-cooled sets have three-wire start
controls.
Standard items and features of the transfer switch are
covered in the first part of this section. Descriptions
of options and accessories appear in the second part.
CABINET
The standard Onan OT cabinet meets requirements
of the National Electrical Manufacturers Association
(NEMA) for a “Type 1” cabinet. This type is desig¬
nated as a general purpose, indoor cabinet. Exterior
itemson atypical OT cabinet are shown in Figure 14.
Indicator Lamps
Two lamps on the cabinet door indicate which power
source is connected to the load. The Normal lamp
when lit indicates the Normal power source is supply¬
ing load. The Emergency lamp will light when the
Emergency power source is supplying the load.
Test Transfer Switch
This switch has three positions and can simulate a
power outage for test purposes. In the Normal posi¬
tion, the transfer switch is set for automatic opera¬
tion. Moving the switch to Test sends a start signal to
the generator set. The generator set will start and
assume load as long as the switch is in this position.
Moving the switch to Normal causes load transfer to
the Normal power source after the retransfer time
delay expires (see Control section for time delay des¬
cription). To avoid the delay and have fast retransfer
of load to the Normal power source, the switch can be
moved to the Retransfer position.
OPTIONAL
FREQUENCY METER
(FOR EMERGENCY
POWER SOURCE)
OPTIONAL AC VOLTMETER
(FOR EMERGENCY POWER SOURCE)
NORMAL POWER SOURCE
INDICATOR LAMP
EMERGENCY POWER SOURCE
INDICATOR LAMP
OPTIONAL AC AMMETER
(FOR EMERGENCY POWER SOURCE)
PHASE SELECTOR SWITCH
(FOR USE WITH OPTIONAL
AC VOLTMETER AND AC AMMETER
ON THREE-PHASE SYSTEMS)
OVERCRANK LAMP/RESET
WITH THREE-WIRE START
OPTION ONLY
LOCKING DOOR
HANDLE FOR CABINET
STOP/AUTO/HAND CRANK
SELECTOR SWITCH — WITH
THREE-WIRE START OPTION ONLY
TEST/NORMAL/RETRANSFER
SWITCH*
OPTIONAL RUNNING
TIME METER (FOR
EMERGENCY POWER
SOURCE)
‘KEY-OPERATED
FIGURE 14. OT CABINET WITH OPTIONS

TRANSFER SWITCH
The transfer switch opens and closes the contacts
that transfer the load between Normal and Emer¬
gency power. The transfer switch is mechanically
interlocked to prevent simultaneous closing to both
power sources. The main parts of the transfer switch
discussed here are the contact assemblies, linear
^actuator, motor disconnect switch, and auxiliary
contacts.
Contact Assemblies
Series OT transfer switches are two or three pole,
with a neutral block. The contact assemblies make
and break the current flow. When closed to either
Normal or Emergency power source, the contacts are
mechanically held. A mechanical interlock prevents
them from closing to both power sources at the same
time.
Linear Actuator
The linear actuator is a linear induction motor that
actuates the contact assemblies. It moves the contact
assemblies between the Normal power source and
Emergency power source as required. The linear
actuator operation is initiated automatically with
automatic transfer switches. Manual operation of the
transfer switch is possible. Refer to manual operation
in the OPERATION section.
Motor Disconnect Switch
The motor disconnect toggle switch opens and
closes the linear actuator circuit. It is located on the
transfer switch panel as in Figure 3. It is placed in the
down position for manual operation and the up posi¬
tion for automatic operation.
Auxiliary Contacts
Auxiliary contacts are provided on the Normal and
Emergency side of the transfer switch. They are actu¬
ated by operation of the transfer switch during
transfer and retransfer. The auxiliary contacts have
current ratings of 10 amperes at 480 VAC.
ELECTRONIC CONTROL
This section describes the standard electronic con¬
trol. A description of the basic circuits follows.
Starting Circuits
The starting circuit is a basic supervisory function of
the OT control. Water-cooled Onan generator sets
use a two-wire start control.
Although the logic is more involved, the two-wire
starting circuit can be thought of as a single pole,
single throw switch. A closed switch signals the gen¬
erator set to start. An open switch signals the electric
generator set to stop. The starting battery of the gen¬
erator set provides the operating voltage.
An OT option is available for Onan air-cooled generator sets which
require a three-wire starting control. See OPTIONS later in this
section for a description.
Time Delays
Start Time Delay: is adjustable from zero to six
seconds. This brief time delay (factory set at two
seconds) prevents generator set starting from power
interruptions of short duration. Timing starts the
moment of Normal power interruption. If the duration
of interruption exceeds the delay time, the OT signals
the generator set to start.
Stop Time Delay: is adjustable from zero to eight
minutes, is factory set for five minutes. It begins tim¬
ing when the load is retransferred to the Normal
power source. At the end of delay, the stop signal is
sent to the generator set. This time delay allows the
generator set to cool down at no load before
stopping.
Transfer Time Delay: begins when generator voltage
and frequency reach the settings of the control. After
the delay, the transfer switch transfers the load to the
Emergency power source. This brief time delay (fac¬
tory set at two seconds) allows the generator set to
stabilize before load is applied. It has an adjustable
range of zero to two minutes.
Retransfer Time Delay: is factory set for 15 minutes
and begins the moment Normal line voltage and fre¬
quency return. After the delay, the transfer switch can
retransfer the load to the Normal source. The delay
allows the Normal source to stabilize before re¬
transfer. It has an adjustable range of 0 to 32 minutes.
14

Undervoltage Sensing
If the monitored source voltage falls to the dropout
point, a signal from the time delay module tranfers
the load to the other power source (if present and
within acceptable limits). The time delay module
logic looks at the source OK signals from both sour¬
ces and decides which one to transfer to after the-
appropriate time delay. The undervoltage sensor
only decides if the source it is monitoring is OK.
The sensors are factory set to pick up at 95 percent of
the nominal voltage and drop out at 85 percent. The
pickup setting is adjustable from 85 to 100 percent of"
the nominal voltage, and the dropout setting from 75
to 98 percent of the pickup voltage.
To transfer load to the Normal power source, for
example, the Normal source voltage would have to be
95 percent of the nominal voltage. Once connected,
the voltage sensor would not signal for a drop of load
unless Normal voltage fell below 85 percent of the
pickup voltage.
The standard OT will have undervoltage sensing for
all phases of the Normal and Emergency power
source.
Options
Three Wire Starting Control: A three-wire starting
control enables the transfer switch to start and stop a
three-wire start generator set (Onan air-cooled). See
Figure 15. Three-wire starting logic is similar to a
single-pole, double-throw switch. A common is
closed to one side to send a start signal, and to the
opposite side to send a stop signal. In addition to start
and stop functions, the control has an Overcrank
Relay, Overcrank Lamp/Reset Switch, and Auto/Stop/
Hand Crank Switch described below.
Overcrank Relay: (Figure 15) protects the
engine starter motor by limiting cranking
time. If the generator set does not start within
the adjustable time limit (up to 60 seconds),
the relay opens the starting circuit. The Over¬
crank lamp lights to indicate an overcrank
condition.
Overcrank Lamp/Reset Switch: is located on
the cabinet door, Figure 14, and is operated
by the overcrank relay. It lights to indicate the
engine starting circuit has opened. After the
starting problem is corrected, the circuit is
reset by pushing the lamp inward and
releasing.
Auto/Stop/Hand Crank Switch: is located on
the cabinet door, Figure 14. Thisswitch is the
operation selector switch for the three-wire
start Onan generator set. The three positions
Auto, Stop, and Hand Crank, function as
follows:
AUTO: Allows the generator set to
start and assume the load if a
power outage occurs. This is
the normal operating posi¬
tion.
STOP: Shuts down the generator
set and prevents it from
starting. Use this position
when servicing the genera¬
tor set.
HAND CRANK: Prevents the automatic
transfer switch from starting
the generator set but allows
starting and stopping at the
set. Use this position for
generator set maintenance.
15

EXERCISER
PROGRAMMED
TRANSITION
THREE WIRE
STARTING CONTROL
OVERCRANK RELAY
PREHEAT
TIME DELAY
BATTERY CHARGER
FIGURE 15. OT OPTIONS WITHIN CABINET
Generator Failure Contact
(Three-Wire Starting Only): This option has a two-
place terminal connection for a remote signal device
to indicate a generator failure such as an overcrank
condition described previously. The relay with this
contact is located within the three wire starting
control.
Preheat Time Delay (Three-Wire Starting Only): If the
application requires, a time delay relay can be
installed which delays cranking of a three-wire start
Onan diesel generator set for preheating (Figure 15).
This relay prevents the engine starter motor from
functioning until the adjustable preheat time delay,
0.6 to 60 seconds, is complete.
Exerciser: The exerciser initiates generator set start¬
ing and exercising for preheat intervals. See Figure
15. It is a fourteen-day, twenty-four hour clock. A
large dial divides the twenty-four hour day into
fifteen-minute intervals. Asmallerspoked dial divides
two weeks into one-day segments. Placement of trip
cms in the diai faces determines exercise periods.
Preferably, the generator set should have load during
the exercise periods. However, the With Load/With¬
out Load selector switch on the exerciser gives the
option of exercise load conditions. The With Load
position means the generator set will assume any
loads (during exercise periods) that normally are
supplied through the transfer switch from the utility.
Battery Charger: An OT automatic transfer switch
can be equipped with either a float battery charger or
a trickle battery charger. Both can be used with lead-
acid or nickel-cadmium batteries.
Float Battery Charger: A float-charge batter
charger regulates its charge voltage to con ¬
tinuously charge without damage to the bat
tery. As the battery approaches full charge,
the charging current automatically tapers to
zero amperes or to steady-state load on the
battery. The battery charger has an ammeter
for indication of charging current and has a
fuse for protection of the battery charger
circuit.
16