AT120A, AT140A, AT150A, AT175A
Universal Transformers
INSTALLATION INSTRUCTIONS
APPLICATION
Code Class 2 “not wet” and Class 3 “wet” requirements
and are Underwriters Laboratories (UL) Inc. listed under
UL 1585. They can be mounted through a 7/8 in. knock-
out on the accessory mounting plate (included), or with
the integral mounting feet. See Table 1 for additional
specifications.
These transformers are for use in 24 Vac nominal control
circuits. They are typically used in heating/cooling control
systems but can be used in any application that does not
exceed the load ratings. They meet National Electrical
Table 1. Model Specifications.
Primary
Secondary
Voltage
Input
Voltage
(60 Hz)
At Rated
Power
Output
Output Rating at
100 Percent Power
Factor
Model
Number
Wiring
Connections
Open
Circuit
Wiring
connections
AT120A
120/208/
240
9 in. leads
27.0
24.0
Screw
terminals
20 VA
AT140A
120
9 in. leads
27.0
24.0
Screw
terminals
40 VA
120/208/
240
120/240
208/240
AT150A
AT175A
120/208/
240
9 in. leads
9 in. leads
27.5
27.5
24.0
24.0
Screw
terminals
50 VA
75 VA
120/208/
240
Screw
terminals
4. After installation is complete, check out product
INSTALLATION
operation as provided in these instructions.
When Installing this Product …
CAUTION
Can cause electrical shock or equipment
damage.
Disconnect power supply before beginning
installation.
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard-
ous condition.
Electrical Hazard.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for
your application.
3. Installer must be a trained, experienced service
technician.
69-0251-3
AT120A, AT140A, AT150A, AT175A UNIVERSAL TRANSFORMERS
WITH RAISED PORTION OF KNOCKOUTS FACING YOU:
1. PRY UP TOP SECTION OF LARGE KNOCKOUT
BY INSERTING SCREWDRIVER FIRST AT ONE
SIDE OF SLOT AND THEN AT THE OTHER SIDE.
M12126
Fig. 3. When screw is tightened, clamp holds
plate on transformer.
THEN PRY UP BOTTOM SECTION OF KNOCKOUT.
2.
MOUNTING PLATE AT LAMINATIONS
1. Remove the large rectangular knockout in the
mounting plate as shown in Fig. 4.
2. Hold the transformer so the clamp on the end bell
faces you.
3. With the keyhole slots up, fit the mounting plate
over the primary leadwires and end bell. Insert
small tab at the bottom of the plate into the slot in
the transformer mounting foot.
4. Insert the mounting screw (supplied) through the
holes as shown in Fig. 5. Secure the plate to the
transformer, but do not overtighten the screw.
MOUNTING TRANSFORMER AND PLATE ON OUTLET BOX
The mounting plate can be mounted on 4 in. square
boxes, 2 x 4 in. rectangular boxes, and on 4 in. octagonal
boxes. See Fig. 4.
3. REMOVE BOTH SECTIONS OF KNOCKOUT WITH PLIERS.
SHADED AREAS REPRESENT KNOCKOUTS
AND SCREW SLOTS USED WITH 2 X 4 INCH
OR OCTAGONAL OUTLET BOXES.
1. Align the plate with the box to determine the correct
mounting holes. The mounting feet and secondary
terminals are outside the box.
2. Remove the mounting hole knockouts, if necessary.
Mount the plate on the outlet box using two screws
(obtained locally).
M9188A
Fig. 4. Use screwdriver to pry out both
sections of knockout.
TRANSFORMER
PLATE
Mounting Through Outlet Box Knockout Hole
The transformer can be mounted on an outlet box using
the clamp on the primary end bell. The mounting plate is
not used. To mount the transformer on an outlet box:
1. Turn the clamp screw almost all the way out.
2. From outside box, thread the primary leadwires
through suitable 7/8 in. knockout. Fit the clamp and
screw through the knockout. Do not mount the
transformer through a plastic knockout.
ANT
T
IMPOR
MOUNT
TRANSFORMER
OTHER SIDE
3. Tighten the clamp screw securely against the rim of
the knockout. Avoid damaging the leadwires with
the screwdriver.
M9163
Fig. 5. Mounting screw and tab hold plate on
transformer.
3
69-0251-3
AT120A, AT140A, AT150A, AT175A UNIVERSAL TRANSFORMERS
5. Do not put system into operation unless correct
Mounting Through Outlet Box Knockout
primary and secondary voltages are measured.
The transformer can be mounted on an outlet box using
the clamp on the primary end bell. The mounting plate is
not used. To mount the transformer on an outlet box:
1. Turn the clamp screw almost all the way out.
2. From outside box, thread the primary leadwires
through suitable 7/8 in. knockout. Fit the clamp and
screw through the knockout. Do not mount the
transformer through a plastic knockout.
SINGLE VOLTAGE MODELS
2
COMMON
BLACK
VOLTAGE
PRIMARY
3
SECONDARY
1
VARIES
WITH MODEL
3. Tighten the clamp screw securely against the rim
of the knockout. Avoid damaging the leadwires
with the screwdriver.
120 V - WHITE
208 V - RED
240 V - ORANGE
277 V - BROWN
480 V - BLACK/RED
120/240 MODELS
WIRING
2
COMMON
BLACK
All wiring must comply with local codes and ordinances.
Disconnect power before making wiring connections to
prevent electrical shock or equipment damage.
1. Make primary connections to the line voltage
power supply. On multitap models, be sure to use
correct leads for available power supply. See
Fig. 6.
2. On multitap models, insulate the ends of the
unused leads using wire nuts or capping with a
solderless connector.
120 V
WHITE
PRIMARY
3
SECONDARY
1
240 V
ORANGE
208/240 VAC MODELS
2
COMMON
208 V
240 V
BLACK
3. Make secondary connections to 24 Vac control
circuit.
PRIMARY
3
SECONDARY
1
RED
ORANGE
CHECKOUT
120/208/240 VAC MODELS
2
COMMON
BLACK
120 V
CAUTION
Overload current protection is inherent on
AT120, AT140, and AT150. A fused 3.5 Amp
secondary is used on AT175.
PRIMARY
3
SECONDARY
208 V
240 V
WHITE
RED
Voltage Check Hazard.
1
ORANGE
Do not short transformer secondary terminals.
1
2
3
SECONDARY CONNECTIONS ARE SCREW TERMINALS, 1/4 INCH
QUICK-CONNECTS OR BLUE AND YELLOW LEADWIRES.
BLACK IS COMMON WITH RESPECT TO THE TRANSFORMER
WINDING ONLY AND NOT THE EXTERNAL CIRCUIT.
Voltage Check
After installation is complete, turn on power supply and
perform a voltage check:
SOME MODELS AVAILABLE WITH 1/4 INCH QUICK CONNECTS.
M22974
1. Place controlled equipment in operation and
observe through one complete cycle.
2. Using a voltmeter, check for proper primary and
secondary voltages.
Fig. 6. Schematics for single and multitap
transformers.
3. If voltage readings are incorrect, be sure primary
voltage connections are made correctly.
4. Measure voltage again:
a. If correct primary voltage is measured and
secondary voltage is significantly less than the
voltage shown on the regulation curves,
transformer winding is damaged. Replace
transformer and repeat checkout procedures.
b. If primary voltage is 0V, be sure power supply
is connected correctly or repair, if necessary.
Repeat checkout procedures.
Automation and Control Solutions
Honeywell International Inc.
1985 Douglas Drive North
Golden Valley, MN 55422
customer.honeywell.com
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario M1V 4Z9
® U.S. Registered Trademark
© 2005 Honeywell International Inc.
69-0251-3 G.H. Rev. 06-05
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