1. ecobee Support
2. Thermostats
3. Thermostat Installation & Wiring Diagrams

I currently own a Smart Si and use a Power Extender Kit (PEK). Can I use the same Power Extender Kit for ecobee3 lite?

Unfortunately, no. Because the wiring required for the Smart Si and the ecobee3 lite are different, you’ll have to replace it with the PEK that came with your new ecobee3 lite. Find instructions to do so here.