Powering Thermostats Without a C-Wire (ADC-T3000 / ADC-T2000)
Most thermostats can run on batteries, but hardwiring is preferred for reliability. If your system lacks a C-wire, here are safe options and requirements for Alarm.com Smart Thermostats.
Power Requirements
Thermostat | Voltage | Max Current |
---|---|---|
Alarm.com Smart Thermostat (ADC-T3000) | 24 VAC | Up to 1 A |
Alarm.com Smart Thermostat (ADC-T2000) | 24 VAC | Up to 1 A |
Note: For other thermostat models, confirm voltage and current limits in the manufacturer’s manual.
Typical C-Wire Connections
On 24 VAC systems, one transformer lead lands on R/Rh/Rc and the other on C. Verify the wiring diagram for your specific thermostat and air handler/furnace.
Option: Standalone 24 VAC Transformer (No C-Wire)
The ADC-T3000/T2000 can be powered by an external 24 VAC transformer separate from the HVAC, with limitations:
- Wire transformer leads to R (Rh or Rc, whichever is unused) and C on the thermostat.
- Remove any Rh–Rc jumper if present and follow the thermostat’s configuration prompts.
- Limitation: This setup supports heat-only or cool-only control (not both) when using a standalone transformer for power.
Best Practices
- Confirm transformer output is 24 VAC and adequately rated (≥ the thermostat’s current requirement).
- Secure low-voltage cable runs and strain-relief at the thermostat and transformer.
- If adding a C-wire kit or fishing new cable, power down the HVAC at the service switch/breaker first.
- After wiring, restore power and complete thermostat setup; verify mode and fan operation.
Need Help?
True Protection can assess your wiring, provide options (C-wire add-a-wire kit, transformer, or new cable), and complete a safe install.