Honeywell, AT140A1000/U, Transformer, 120 V, 60 Hz

Honeywell AT140A1000/U 40 VA Transformer – 120V to 24/27V Step-Down Class 2 Transformer

The Honeywell AT140A1000/U is a 40 VA Class 2 transformer designed to supply low-voltage control power to thermostats, gas valves, relays, and other HVAC system components. It converts 120 VAC input to a nominal 24–27 VAC output and is rated for continuous duty in heating and cooling applications. The transformer is suitable for use in residential and light commercial systems and complies with UL 1585 and NEC Class 2 requirements.

This unit is configured for versatile mounting and includes multiple wiring termination methods, making it adaptable for both replacement and new construction installations.

Functional Details

• Primary Voltage: 120 VAC, 60 Hz
• Secondary Voltage: 24–27 VAC
• Power Rating: 40 VA
• Frequency: 60 Hz
• Class: NEC Class 2 rated
• Compliance: UL 1585 listed

Physical Specifications

• Dimensions: 3-3/16" H x 2-3/8" W x 3-1/8" D
• Temperature Range: -20°F to 105°F (-29°C to 40°C)
• Mounting Types: Foot mount, plate mount, clamp mount, or panel mount
• Primary Wiring: Color-coded lead wires
• Secondary Wiring: Screw terminal connections

Installation Requirements

The transformer must be installed by qualified personnel familiar with electrical wiring and local code compliance. Ensure correct input voltage and appropriate load calculations prior to energizing the circuit. Secure mounting and clear identification of primary and secondary connections are essential to system reliability and service safety.

Contractor Notes

The Honeywell AT140A1000/U is widely used for retrofit and replacement in HVAC controls requiring low-voltage power. Its 40 VA rating supports most single-zone heating/cooling control circuits and is compatible with a wide range of thermostats and relays. Multiple mounting configurations simplify installation across a variety of system designs.