resideo AT120A User manual

PRODUCT DATA
68-0054-06
AT120A-E; AT140A-E; AT150A,B,D-F;
AT160B; AT175A-D,F Transformers
APPLICATION
These general purpose transformers provide power to 24 Vac
circuits. They are typically used in heating/cooling control
systems, but can be used in any application that doesn’t
exceed the load ratings.
FEATURES
• AT120 is rated at 20 VA.
• AT140 is rated at 40 VA.
• AT150 is rated at 50 VA.
• AT160 is rated at 60 VA.
• AT175 is rated at 75 VA.
• All models meet National Electrical Code Class 2 not wet,
Class 3 wet transformer requirements.
• All models conform to Underwriters Laboratories Inc.
Standard UL 1585.
• Color-coded leadwires for primary connections and screw
terminals for secondary connections, fixed 1/4 inch
(6 mm) male quick-connects or color-coded leadwires for
both primary and secondary, are standard.
• Models available with stripped leadwires, leadwires with
variety of terminals, or special terminations as required on
both primary and secondary.
• Mounting options include clamp mounting on outlet box
knockout, plate mounting, foot mounting, panel
mounting, conduit/panel and a combination.
• Models available for 120V, 240V, 277V, 480V, 120/240V,
208/240V, 277/480V, 120/208/240V, 208/240/480V, or
208/277/480V supply at 60 Hz.
• “F” models include a button for manually resetting the
circuit breaker.
M38595
Contents
Application .......................................................................... 1
Features .............................................................................. 1
Specifications ..................................................................... 2
Installation .......................................................................... 8
Checkout ............................................................................. 12

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
68-0054—06 2
SPECIFICATIONS
IMPORTANT
The specifications given in this publication do not
include normal manufacturing tolerances. Therefore,
a sample unit may not match the listed specifica-
tions exactly. Also, this product is built and tested
under closely controlled conditions, and some minor
differences in performance can be expected if those
conditions are changed.
Models: AT120A-E; AT140A-E; AT150A,B,D-F; AT160B;
AT175A-D,F.
Electrical Ratings: See Table 1.
aRefer to regulation curves.
bVoltage is 27.0V on AT150F and AT175F models.
Wiring Connections:
“A”, “C”, and “D” models: Primary—9 inch (230 mm) leadwires;
Secondary—screw terminals.
“B” and “E” models: Primary—9 inch (230 mm) leadwires or
fixed 1/4 inch (6 mm) quick-connects. Different length
leadwires and leadwires with stripped ends or with termi-
nals attached also available. Specify when ordering.
Secondary—9 inch (230 mm) leadwires or fixed 1/4 inch (6
mm) quick-connects. Different length leadwires, leadwires
with stripped ends or with terminals attached, and screw
terminals also available. Specify when ordering.
“F” models: Primary and Secondary—9 inch (230 mm) lead-
wires.
Mounting Means:
Dimensions: See Fig. 1 through 5.
Regulation:
See transformer regulation curves, Fig. 6 through 10.
Overcurrent Protection:
Inherent on AT120, AT140, and AT150. Thermal fusible link on
AT160 and AT175. Circuit breaker on AT150F and AT175F
models.
Approvals:
UNDERWRITERS LABORATORIES INC. LISTED (“A”, “C” and “F”
models): File No. E14881, Guide No. XOKV.
UNDERWRITERS LABORATORIES INC. COMPONENT RECOG-
NIZED (“B,” “D,” “E” models): File No. E14881, Guide No.
XOKV2.
All models conform to Underwriters Laboratories Inc. Stan-
dard UL 1585.
NATIONAL ELECTRICAL CODE: Class 2 not wet, Class 3 wet.
Optional Specifications:
End bells or caps on “B” through “E” models.
Terminations on “B” through “E” models.
Circuit breaker reset button on “F” models.
National Electrical Code:
Class 2 not wet, Class 3 wet
Table 1. Electrical Ratings.
Model
Number
Output Rating at
100 Percent Power
FactoraPrimary Input Voltage
(60 Hz)
Secondary Output Voltage
Open Circuit At Rated Power Output
AT120 20 VA 120, 240, 277, 480, 120/240,
208/240, 240/277, 277/480,
120/208/240, 208/240/480,
or 208/277/480V
27.0 24.0
AT140 40 VA
AT150 50 VA 27.5b
AT160 60 VA
AT175 75 VA
Model Suffix
Letter Mounting Means
A Includes clamp for outlet box knockout, 4 x 4 inch mounting plate for 2 x 4 inch or 4 x 4 inch outlet box, and
mounting feet for surface mount.
B Foot-mounted.
C Includes clamp for outlet box knockout.
D Integral 4 x 4 inch mounting plate fits 2 x 4 inch or 4 x 4 inch outlet box.
E Panel mounted with two No. 8 screws (not included).
F Includes 1/2-14 NPSM conduit connector and lock nut for mounting on plate or panel (not included) with 7/8 in.
knockout, and mounting feet for surface mount.

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
368-0054—06
Fig. 1. “A” model transformer dimensions in in. (mm).
1
Model
AT120
AT140
120, 208/240V
120/208/240V
AT150
AT175
in.
2-3/4
3
3
3
3-1/2
mm
70
76
76
76
89
in.
1-7/8
2
2
2-1/8
2-9/16
mm
48
51
51
54
65
in.
2-15/16
3-1/8
3-1/8
2-15/16
3-5/8
mm
75
79
79
75
92
ABCD
in.
1-7/16
1-9/16
1-3/4
1-3/4
2-1/8
mm
37
40
44
44
54
FOR AT120 MODELS, 1-15/16 (49).
FOR AT120 MODELS, 2-7/8 (73).
2
3FOR AT120 MODELS, 1-7/16 (37).
FOR AT120 MODELS, 1-7/8 (48).
4
3
4
A MAX.
M12123B
1
(44)
3
4
2
(60)
3
8
3
8(10)
3
16
(5)
PLATE OR OUTLET BOX MOUNTED
AT CLAMP ON END BELL
B MAX.
1
16
1 (27)
PLATE MOUNTED
AT THE LAMINATIONS
2
C MAX.
1
2
(57)
1
4
3
(81)
3
16
11
16 (22)
3
4(19)
FOOT MOUNTED
D

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
68-0054—06 4
Fig. 2. “B” and “E” model transformer dimensions in in. (mm).
Fig. 3. Mounting plate dimensions in in. (mm). Mounting plate is shipped with “A” model transformers and attached on “D” model
transformers.
D
B
G
(MAX)
F
E
3/8
(10)
A
C
3/16
(5)
3
1
2
4
1
1
Model
AT120
AT140
AT150
AT160
AT175
in.
2-13/16
3-1/8
3-1/8
3-1/8
3-1/8
mm
71
79
79
86
86
in.
1
7/8
7/8
1-3/8
1-3/8
mm
25
22
22
35
35
in.
3/16
3/16
7/32
7/32
7/32
mm
5
5
6
6
6
ABCDEFG
in.
15/16
13/16
7/8
1-1/4
1-7/16
mm
24
21
22
32
37
in.
1-5/8
2-1/4
2-1/4
2-1/4
2-1/4
mm
41
57
57
57
57
in.
1-7/8
2-9/16
2-9/16
2-9/16
2-9/16
mm
48
65
65
65
65
in.
1-3/4
1-11/16
1-3/4
2-1/4
2-1/4
mm
44
42
44
57
57
"B" MODELS AVAILABLE WITH
MOUNTING FEET; "E" MODELS
ARE LESS MOUNTING FEET.
AVAILABLE WITH LEADWIRES OR
FIXED 1/4 in. [6 mm] MALE QUICK-
CONNECTS. SCREW TERMINALS
AVAILABLE ON SECONDARY.
MOUNTING HOLES STANDARD
ON "E" MODELS ONLY.
1/4 in. (6 mm) ON AT175B.
2
3
4
1/16
(2)
M12107A
M12124B
2
(60)
3
8
1
8
(3)
2
(52)
1
16
1
4
(6)
3
16
(5)
4
(106)
3
16
3
(86)
3
8
3
8
3 (86)
1
4
3 (83)
5
16(8)
1
8(3)

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
568-0054—06
Fig. 4. “C” and “D” model transformer dimensions in in. (mm).
D
B
C
A
1
1
Model
AT120
AT140
AT150
AT175
in.
1-7/8
2-1/4
2-1/4
2-1/4
mm
48
57
57
57
in.
13/16
1-1/16
1-1/16
1-1/2
mm
21
27
27
38
in.
1-15/16
2-1/4
2-1/4
2-1/4
mm
49
57
57
57
ABCD
in.
2-1/4
2-5/8
2-5/8
2-5/8
mm
57
67
67
67
SECONDARY AVAILABLE WITH LEADWIRES, FIXED 1/4 in. (6 mm)
MALE QUICK CONNECTS, OR SCREW TERMINALS.
PRIMARY ON "D" MODELS AVAILABLE WITH LEADWIRES
OR FIXED 1/4 in. (6 mm) MALE QUICK CONNECTS.
2
M12122B
1
4
1 (32)
7
8(22) 7
8(22)
SIDE VIEW
TOP VIEW
"C" MODEL
B
D
C
2
1
2
(60)
3
8
2
(52)
1
16
1
4
(6)
3
16
(5)
4
(106)
3
16
3
(86)
3
8
3
8
3 (86)
7
16
1 (37)
1
4
3 (83)
5
16(8)
1
8(3)
7
8(22)
FRONT VIEW SIDE VIEW
"D" MODEL
TRANSFORMER MOUNTED
ON OUTLET BOX KNOCKOUT

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
68-0054—06 6
Fig. 5. “F” model transformer dimensions in in. (mm).
Fig. 6. AT120 regulation curve. Fig. 7. AT140 regulation curve.
A
7/16
(11)
B
M12115A
7/16
(11)
11/16 (17)
3-3/16
(81)
2-3/16 (56)
C
Model
AT150F
AT175F
in.
1-3/4
1-3/4
mm
45
45
in.
1-3/4
2-1/8
mm
45
54
in.
3-5/8
3-15/16
mm
93
102
ABC
1.00.5 1.50 3.0 3.52.0 2.5
15
20
25
30
35
SECONDARY CURRENT (AMPS)
SECONDARY VOLTAGE (VOLTS)
M12110A
AT120 REGULATION
1.00.5 1.50 3.0 3.52.0 2.5
15
20
25
30
35
SECONDARY CURRENT (AMPS)
SECONDARY VOLTAGE (VOLTS)
M12111A
AT140 REGULATION

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
768-0054—06
Fig. 8. AT150 regulation curve.
Fig. 9. AT160 regulation curve.
Fig. 10. AT175 regulation curve.
1.00.5 1.50 3.0 3.52.0 2.5
15
20
25
30
35
SECONDARY CURRENT (AMPS)
SECONDARY VOLTAGE (VOLTS)
M12112A
AT150 REGULATION
1.00.5 1.50 3.0 3.52.0 2.5
15
20
25
30
35
SECONDARY CURRENT (AMPS)
SECONDARY VOLTAGE (VOLTS)
M12113A
AT160 REGULATION
1.00.5 1.50 3.0 3.52.0 2.5
15
20
25
30
35
SECONDARY CURRENT (AMPS)
SECONDARY VOLTAGE (VOLTS)
M12114A
AT175 REGULATION

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
68-0054—06 8
INSTALLATION
When Installing this Product…
1. Read these instructions carefully. Failure to follow them
could damage the product or cause a hazardous condi-
tion.
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 techni-
cian.
4. After installation is complete, check out system opera-
tion as suggested in these instructions.
CAUTION
Disconnect power supply before beginning installation
to prevent electrical shock or equipment damage.
Foot Mounting (“A”, “B”, and “F” Models
Only)
Mount using screws (not supplied) through the two (“B”
models) or four (“A”, “F” models) holes in the mounting feet.
Refer to Fig. 11. Line voltage primary connections must be
made within an approved electrical enclosure. Discard the
mounting plate (“A” models only).
Plate Mounting (Refer to Fig. 12) (“A”
and “D” models only) Mounting Plate to
Transformer (“A” models only)
Mount the plate to the transformer either:
a. at the clamp on the primary end ball…OR…
b. at the laminations.
Fig. 11. Foot mounting.
M12125B
USE SCREWS OR BOLTS
THROUGH SLOTS (4) IN
MOUNTING FEET
USE SCREWS OR BOLTS
THROUGH HOLES IN
MOUNTING FEET
"F" MODELS
"B" MODELS
"A" MODELS
USE SCREWS OR BOLTS
THROUGH SLOTS (4) IN
MOUNTING FEET

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
968-0054—06
Fig. 12. On “A” models, plate may be mounted to transformer
in either of two positions. On “D” models, plate is factory-
mounted at laminations.
To Mount Plate at Primary End Bell:
1. Turn the screw on the clamp almost completely out.
2. Hold the mounting plate with the keyhole slots up and
the raised portion of the large center knockout away
from you.
3. From the back, thread the primary leadwires through the
round center hole in the plate.
4. Fit the clamp and screw through the round hole.
5. While holding the plate in place, tighten the setscrew
securely against the rim of the hole. Refer to Fig. 13.
Avoid damaging the leadwires with the screwdriver.
Fig. 13. When screw is tightened, clamp holds plate on
transformer.
PLATE MOUNTED AT CLAMP ON PRIMARY END BELL
MOUNTING
PLATE
MOUNTING PLATE
PLATE MOUNTED AT THE LAMINATIONS
M12109A
END
BELL
CLAMP SCREW
AND CLAMP
RAISED PORTION OF
LARGE CENTER KNOCKOUT
LEADWIRES
FOR PRIMARY
CONNECTIONS
LEADWIRES
FOR PRIMARY
CONNECTIONS
MOUNTING
SCREW SCREW
TERMINALS FOR
SECONDARY
CONNECTIONS
SCREW
TERMINALS FOR
SECONDARY
CONNECTIONS
MOUNTING FEET ON "A" MODELS ONLY.
1
1
1
M12126A

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
68-0054—06 10
Fig. 14. screwdriver to pry out both sections of knockout.
To Mount Plate at Laminations:
1. Remove the large rectangular knockout in the mounting
plate as shown in Fig. 14.
2. Hold the transformer with the clamp on the end bell fac-
ing you.
3. With the keyhole slots up, fit the mounting plate over the
primary leadwires and the end bell. Insert the small tab
at the bottom of the plate into the slot in the transformer
mounting foot.
4. Insert the mounting screw (provided) through the holes
as shown in Fig. 15. Secure the plate to the transformer,
but do not overtighten the screw.
Fig. 15. Secure plate on transformer with mounting screw and
tab.
Mounting Transformer and Plate on Outlet Box
The mounting plate may be mounted on 4 inch square boxes,
2 x 4 inch rectangular boxes, and on 4 inch octagonal boxes.
1. Line up the plate with the box to determine the proper
mounting holes. The mounting feet and secondary ter-
minals will be outside the box.
2. Remove the mounting hole knockouts if necessary.
3. Mount the plate on the outlet box using two screws
(obtain locally).
Mounting Through Outlet Box Knockout
(“A” and “C” Models Only)
The transformer can be mounted on an outlet box using the
clamp on the primary end bell. The mounting plate (“A”
models only) is not used. To mount the transformer on an
outlet box:
1. Turn the clamp screw almost completely out.
2. From outside box, thread the primary leadwires through
suitable 7/8 inch knockout. Fit the clamp and screw
through the knockout.
3. Tighten the clamp screw securely against the rim of the
knockout. Avoid damaging the leadwires with the
screwdriver.
Panel Mounting (“E” Models Only)
“E” model transformers are designed for mounting inside a
panel using No. 8 screws and washers (obtain locally) through
at least two of the four holes in the laminations. Refer to
Fig. 16.
M9188B
WITH RAISED PORTION OF KNOCKOUTS FACING YOU:
PRY UP TOP SECTION OF LARGE KNOCKOUT
BY INSERTING SCREWDRIVER FIRST AT ONE
SIDE OF SLOT AND THEN AT THE OTHER SIDE.
1.
THEN PRY UP BOTTOM SECTION OF KNOCKOUT.
2.
REMOVE BOTH SECTIONS OF KNOCKOUT WITH PLIERS.3.
SHADED AREAS REPRESENT KNOCKOUTS
AND SCREW SLOTS USED WITH 2 X 4 INCH
OR OCTAGONAL OUTLET BOXES.
IMPORTANT
MOUNT
TRANSFORMER
OTHER SIDE
M9163A
TRANSFORMER
PLATE

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
11 68-0054—06
Fig. 16. Mounting “E” model transformer in a panel cutout.
Conduit/Panel Mounting
Mount the transformer on a plate or panel (not included) with
a 7/8 in. knockout. The transformer has a 1/2-14 NPSM
conduit connector and lock nut.
NOTE: To meet UL requirements, mount the transformer on
a plate or panel with a maximum thickness of 0.15 in.
This allows three and one-half threads of the conduit
spud to be exposed after the transformer is mounted.
1. With the conduit connector side of the transformer fac-
ing the plate, thread the leadwires through the plate
knockout.
2. Insert the connector in the knockout.
3. While holding the plate in place, assemble and tighten
the lock nut to fasten the transformer securely. See
Fig. 17. Avoid damaging the leadwires with the screw-
driver.
4. Make line voltage primary connections within an
approved enclosure.
Fig. 17. Conduit/panel mounting (plate not included).
Fig. 18. Schematic for single and multitap transformers.
WIRING
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, make sure to use the cor-
rect leads or terminals for the available power supply.
Refer to Fig. 18.
2. On multitap models with leadwires, insulate the ends of
the unused leads by taping or capping with a solderless
connector.
3. Make secondary connections to 24 Vac control circuit.
M12127A
MOUNTING
PLATE (NOT
INCLUDED)
END
BELL
LEADWIRES
FOR PRIMARY
AND SECONDARY
CONNECTIONS
LOCK NUT
CONDUIT
CONNECTOR
M6906
A
RESET
BUTTON
VOLTAGE
VARIES
WITH MODEL
2
SECONDARY
M12108B
COMMON
PRIMARY
BLACK
120V - WHITE
208V - RED
240V - ORANGE
277V - BROWN
480V - BLACK/RED
1
3
SINGLE VOLTAGE MODELS
208V
2
SECONDARY
COMMON
PRIMARY
BLACK
ORANGE
1
3
208/240 VAC MODELS
240V RED
208V
120V
2
SECONDARY
COMMON
PRIMARY
BLACK
ORANGE
1
1 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.
SOME MODELS AVAILABLE WITH 1/4 INCH QUICK-CONNECTS.
2
3
3
120/208/240 VAC MODELS
240V RED
WHITE
277V
208V
2
SECONDARY
COMMON
PRIMARY
BLACK
BLACK/RED
1
208/277/480 VAC MODELS
480V BROWN
RED

AT120A-E; AT140A-E; AT150A,B,D-F; AT160B; AT175A-D,F TRANSFORMERS
© 2021 Resideo Technologies, Inc. All rights reserved.
This product is manufactured by Resideo Technologies, Inc. and its affiliates.
www.resideo.com
Resideo Technologies, Inc.
1985 Douglas Drive North, Golden Valley, MN 55422
1-800-468-1502
68-0054—06 M.S. Rev. 03-21 | Printed in United States
CHECKOUT
CAUTION
Do not short transformer secondary terminals.
Overload current protection inherent on AT120,
AT140, and AT150. 3.5 Amp fuse available on AT160B
and AT175A-D.
Voltage Check
After installation is complete, turn on power supply and
perform a voltage check.
1. Place the controlled equipment in operation and
observe through one complete cycle.
2. Using a voltmeter, verify proper primary and secondary
voltages.
3. If voltage readings are incorrect, ensure primary volt-
age connections are made properly (refer to Fig. 18).
4. Measure voltage again.
a. If proper primary voltage is measured and second-
ary voltage is significantly less than the voltage
shown on the regulation curves, transformer wind-
ing is damaged. Replace transformer and repeat
checkout procedures.
b. If primary voltage is 0V, make sure power supply is
connected properly or repair if necessary. Repeat
checkout procedures.
5. Do not put the system into operation unless correct
primary and secondary voltages are measured.
Circuit Breaker (AT150F, AT175F
Models only)
Overloading the AT150F or AT175F Transformer results in
tripping the circuit breaker. If the secondary side of the
transformer is short circuited, the circuit breaker trips in less
than one minute. Reset the circuit breaker by pressing the
reset button on the top of the transformer. It can take up to
one hour for the transformer to cool, allowing it to reset. If the
circuit breaker continues to trip, thoroughly check the system
for short circuits and the current draw.