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A common wire (C)  is required for 
5-wire thermostats. If there are only 4 
wires to your existing thermostat (i.e. 
there is no C wire), you can use the 
ecobee Power Extender Kit to power 
your thermostat. 

Step 1. Install Wiring Harness

The Power Extender wiring harness must be installed in an indoor, dry 
location, near the HVAC equipment. When choosing a location, the 
distance between the wiring harness and the HVAC equipment must not 
exceed 24 inches (0.6 m) .

This equipment is sensitive to electrostatic discharge (ESD). Before 
starting, discharge your body of static electricity by touching a 
grounded metal object. Always hold the devices by their edges 
and do not touch any of the internal components. 

1.  Power off the HVAC equipment. 

2.  Remove the top cover of the wiring harness by gently squeezing its 

sides.

3.   Use 2 #6 pan-head screws or double-sided adhesive to attach the 

wiring harness to a flat surface (for example, the furnace casing).

!

Step 2. Install Diode

The diode is designed to be installed behind the thermostat, within the 
thermostat’s backpanel wire opening.

1.  Use your fingers to gently pry the thermostat away from its base.

2.  Using the thermostat’s backpanel wire opening as a guide, gently 

bend the diode wires 90 degrees so that they can be inserted into the 
W O/B and Y terminals:

 

The diode itself should stay within the wire opening.

3.  Clip the diode legs so that you can insert them into the W and Y 

terminals. DO NOT over clip the legs.

4.  Connect the diode legs to the W O/B and Y terminals.

Y N/C

W

O/B

G

RC

RH

C

Y2

W2

AUX

W

Y

N/C

G

RC

RH

C

Y2

W2

AUX

W

Y

W

O/B

Y

Wiring Channel

Removeable Cover

Power Extender Kit

W

Y

Diode

G

C

W

Y

RH

RC

G

C

W

Y

RH

RC

STAT

EQUIP

Thermostat Side

HVAC Side

Mounting Hole

Mounting Hole

Power Extender Kit 

User Manual

Wiring Harness

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