How do I identify and label wires in my gang box?

Warning: Any work with high voltage equipment can be dangerous or even fatal. It should be performed by a qualified electrician. Please ensure that you comply with local electrical codes and regulations. Improper installation can lead to device failure and even cause a fire. Damage to thermostat due to improper installation is not covered under warranty.

Firstly, make sure to have the breaker turned off before removing your existing thermostat form the gang box. This helps protect you during installation. Line voltage thermostats such as Mysa are connected to dangerous voltages. 

This article presents two methods to determine which cables you need to hook up Mysa. Method 1 is based on rules of thumb, and method 2 is based on verifying with a voltmeter/multimeter.

Method One

Below are tips that may help you identify what wires are supply wires, heater load wires, neutral wires, etc. Please note the tips below assume an electrician has installed the gang box and wiring according to national building code and standards (especially when it comes to colours of the heater cables and wires). Sometimes, electricians use different colours or switch colours around.

Step 1:

Pull out all the wires from gang box, so it is easier for you to see what is there.

Count how many heater cables are coming into your gang box. In other words, how many cables (or bundles of wires) are entering the gang box? The picture below has four wires, but only two cables.

Mysa_Installation_Diagrams_2C-B_W.png

Step 2:

Two Cables

If there are only two heater cables, the answer is pretty straightforward:

  • One heater cable is coming from the electrical panel (most commonly the top one)
    • This cable should have two wires coming out of it;  one black wire and either one red (240V) or white (120V) wire
  • One heater cable is going to the baseboard heater
    • This cable should have two wires coming out of it;  one black wire and either one red (240V) or white (120V) wire

Wire up Mysa. Remember, if the display doesn't light up once you power up the device, it is likely that you mixed up the supply and load wires. Simply turn off the breaker, remove Mysa from the wall, and switch Mysa's black and red wire around in the gang box.

Three Cables 

If you have more than three heater cables, then you should follow the installation wizard, here. It will guide you through the rules of thumb to get Mysa wired correctly. 

Method 2 

You can determine which cable is coming from the electrical panel and which cables go to the heater by using a voltmeter. Reference the tables to below to determine the identification voltages. To determine if you have a 240 or 120-volt installation, read here.

240V Installations

  Mysa Wires     Gang Box Wires Identification Voltages 
gret.png Mysa White Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.58_PM.png   Second Phase Leg (L2) (240V)  Ground to L2 (120V)
Screen_Shot_2018-10-22_at_1.51.54_PM.png Mysa Black Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Supply Wire (L1)  Ground to L1 (120V)
 Screen_Shot_2018-10-22_at_1.51.58_PM.png  Mysa Red Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Load Wire   Ground to Load (0V)
Screen_Shot_2018-10-22_at_1.52.02_PM.png Mysa Green Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.52.02_PM.png  Group/Copper   N/A

 

120V Installations
Mysa V1-0

  Mysa Wires     Gang Box Wires Identification Voltages
gret.png Mysa White Screen_Shot_2018-10-22_at_1.49.46_PM.png gret.png  Neutral Wire (N) Ground to N (0V)
Screen_Shot_2018-10-22_at_1.51.54_PM.png Mysa Black Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Supply Wire (L1) Ground to L1 (120V)
 Screen_Shot_2018-10-22_at_1.51.58_PM.png  Mysa Red Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Load Wire  Ground to Load (0V)
Screen_Shot_2018-10-22_at_1.52.02_PM.png Mysa Green Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.52.02_PM.png  Group/Copper  N/A

 

Mysa V1-1

Screen_Shot_2018-10-22_at_1.51.58_PM.png Mysa L2 Screen_Shot_2018-10-22_at_1.49.46_PM.png gret.png  Neutral Wire (N)
Screen_Shot_2018-10-22_at_1.51.54_PM.png Mysa L1 Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Supply Wire (L1)
Screen_Shot_2018-10-22_at_1.51.54_PM.png Mysa Load Screen_Shot_2018-10-22_at_1.49.46_PM.png Screen_Shot_2018-10-22_at_1.51.54_PM.png  Load Wire
         

 

 

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