| Frequency | 60 Hz |
| Electrical Ratings | Primary voltage--120 Vac; Secondary voltage--27 V.O.C. |
| Mounting | Foot-mounted |
| Includes | Metal end bells |
| Dimensions | 1 11/16 in. high x 3 3/16 in. wide x 1 3/4 in. deep |
| UL | UL Listed: A,C,F models. File # E14881 |
| CSA | CSA Certified: A & B models. |
| Temperature Range (F) | -20 F to +105 F |
| Approvals, N.E.C. | NEC Class 2 |
| Electrical Connections (Primary)(in.) | 9 in. leadwires |
| Electrical Connections (Secondary)(in.) | 9 in. leadwires |
| Electrical Ratings, Output | 24 Vac at 20 VA |
Description
The AT120B1028 is a control transformer from Resideo (Honeywell Home), 120 Vac primary, 24 Vac secondary, foot mounted.
Almost every heating and cooling control runs on 24 volts, and the transformer is what makes it. It takes line voltage in and delivers the low-voltage supply the thermostat, the zone valves, the relays and the gas valve all share.
Size it by VA, not by voltage. Every device on the control circuit adds load — a zone valve pulls current while it drives, a relay coil holds current the whole time it is energized, a Wi-Fi thermostat draws continuously. A transformer adequate for the original equipment is not automatically adequate after two zones and a smart stat have been added, and the symptom is intermittent.
Filed here under thermostat accessories, but this is a transformer and belongs with them.
- Brand: Resideo (Honeywell Home)
- Manufacturer Part #: AT120B1028/U
- Type: Control transformer
- Primary: 120 Vac
- Secondary: 24 Vac
- Mounting: Foot-mounted
- Rating: 24 Vac at 20 VA
- Leadwires: 9 in. leadwires
- Operating range: -20 F to +105 F
- UPC: 085267034920
- Category: Transformers