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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
Table 1. Model Specifications.
Voltage Wiring Open
Number (60Hz) Connections Circuit
AT120A \ 120/208/ 9 in. leads 27.0
AT140A 120 9 in. leads 27.0
AT150A 120/208/ 9 in. leads 27.5
AT175A 120/208/ 9 in. leads 27.5
When Installing this Product …
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazardous
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for
3. Installer must be a trained, experienced service
At Rated Output Rating at
Power Wiring 100 Percent Power
Output connections Factor
24.0 Screw 20VA
24.0 Screw 40VA
24.0 Screw SOVA
24.0 Screw 75VA
4. After installation is complete, check out product
operation as provided in these instructions.
Can cause electrical shock or equipment
Disconnect power supply before beginning
AT120A. AT140A, AT150A, AT175A UNIVERSAL TRANSFORMERS
The transformer can be mounted in one of three ways:
– foot mounting.
– plate mounting.
– mounting through outlet box knockout hole.
1. Mount the transformer using screws (not supplied}
through the four 3/16 in. x 3/8 in. holes in the
mounting feet. . . .
2. Make line voltage primary connections w1th1n an
approved enclosure. See Fig. 1.
3. Discard the mounting plate.
Fig. 1. Foot mounting.
MOUNTING PLATE TO lRANSFORMER
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
LARGE CENTER KNOO<OUT
PLATE MOUNTED AT THE LAMINATIONS
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
thread the primary leadwires
. through the round center hole in the plate.
Fit the clamp and screw through the round hole. !: While holding the plate in place