resideo AT120A Universal Transformers Instruction Manual

AT120A Universal Transformers
Instruction Manual

APPLICATION

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 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. knockout on the accessory mounting plate (included), or with the integral mounting feet. See Table 1 for additional  pecifications.
Table 1. Model Specifications.

120/208/240
120/240
208/240
AT150A| 120/208/240| 9 in. leads| 28.| 24.0| Screw terminals| 50 VA
AT175A| 120/208/240| 9 in. leads| 28.| 24.0| Screw terminals| 75 VA

INSTALLATION

When Installing this Product… 1. Read these instructions carefully. Failure to follow them could damage the product or cause a haz-ardous condition. 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. 4. After installation is complete, check out product operation as provided in these instructions.

CAUTION
Electrical Hazard. Can cause electrical shock or equipment damage. Disconnect power supply before beginning installation.
Mounting
The transformer can be mounted in one of three ways:

• foot mounting.
• plate mounting.
• mounting through outlet box knockout hole.

Foot Mounting

1. Mount the transformer using screws (not sup-plied) through the four 3/16 in. x 3/8 in. holes in the mounting feet.
2. Make line voltage primary connections within an approved enclosure. See Fig. 1.
3. Discard the mounting plate.

Plate Mounting
MOUNTING PLATE TO TRANSFORMER Mount the plate to the transformer in either of two positions (see Fig. 2):

• at clamp on primary end bell.
• at laminations.

PLATE MOUNTED AT CLAMP ON PRIMARY END BELL

PLATE MOUNTED AT THE LAMINATIONS

MOUNTING FEET ON “A” MODELS ONLY. M9162
Fig. 2. Mounting plate to transformer in either of two positions.
MOUNTING PLATE AT CLAMP ON PRIMARY END BELL

1. Turn the screw on the clamp almost all the way 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 set-screw securely against the rim of the hole. See Fig. 3. Avoid damaging the leadwires with the screwdriver.

Fig. 3. When screw is tightened, clamp holds plate on transformer.

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.

1. Align the plate with the box to determine the cor-rect mounting holes. The mounting feet and sec-ondary terminals are outside the box.
2. Remove the mounting hole knockouts, if neces-sary. Mount the plate on the outlet box using two screws (obtained locally).

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.
3. Tighten the clamp screw securely against the rim of the knockout. Avoid damaging the leadwires with the screwdriver.

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.

2. THEN PRY UP BOTTOM SECTION OF KNOCKOUT.

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.
   M9188A
   Fig. 4. Use screwdriver to pry out both sections of knockout.
   Fig. 5. Mounting screw and tab hold plate on transformer.

Mounting Through Outlet Box Knockout
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.
3. Tighten the clamp screw securely against the rim of the knockout. Avoid damaging the leadwires with the screwdriver.

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, 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.
3. Make secondary connections to 24 Vac control circuit.

CHECKOUT

CAUTION
Voltage Check Hazard. Overload current protection is inherent on AT120, AT140, and AT150. A fused 3.5 Amp secondary is used on AT175. Do not short transformer secondary terminals.
Voltage Check
After installation is complete, turn on power supply and perform a voltage check:

1. Place controlled equipment in operation and observe through one complete cycle.

2. Using a voltmeter, check for proper primary and secondary voltages.

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 OV, be sure power supply is connected correctly or repair, if necessary. Repeat checkout procedures.

5. Do not put system into operation unless correct primary and secondary voltages are measured.

Fig. 6. Schematics for single and multitap transformers.

Resideo Technologies, Inc.
1985 Douglas Drive North, Golden Valley, MN 55422 1-800-468-1502
69-0251-04 M.S. Rev. 08-20 I Printed in United States
www.resideo.com
© 2020 Resideo Technologies, Inc. All rights reserved.
This product is manufactured by Resideo Technologies, Inc. and its affiliates.

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