Wiring Reference Guide
Warning: Mysa for In-Floor Heating operates on line voltage (120V or 240V). Working with line voltage electricity is dangerous and can result in serious injury or death. Turn off the breaker and verify power is off before making any connections. If you're not confident in your electrical skills, hire a licensed electrician.
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Terminal Overview
Your Mysa for In-Floor Heating has distinct terminal groups for power and sensors:
- LINE terminals — Connect to your circuit breaker (power source)
- LOAD terminals — Connect to your floor heating system
- Sensor terminals — Connect your floor temperature sensor
- Ground connection — Safety ground wire
Keep these separate. Mixing them up will prevent your thermostat from working.
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LINE Terminals (Power In)
The LINE terminals receive power from your circuit breaker.
120V Wiring
- L1 — Hot wire from circuit breaker
- L2/N — Neutral wire from circuit breaker
240V Wiring
- L1 — First hot wire from circuit breaker
- L2 — Second hot wire from circuit breaker (no neutral on 240V)
Important: On 240V circuits, you use both L1 and L2 as hot wires. There is no neutral connection.
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LOAD Terminals (Power Out)
The LOAD terminals send power to your floor heating system.
120V Configuration
- Load — Single wire to your floor heating system
240V Configuration
- Load — Both L1 and L2 carry power to your floor heating system
Critical: LOAD terminals must connect only to your heating system, never to the breaker.
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Floor Sensor Terminals
The sensor terminals (separate from power wiring) connect your floor temperature sensor.
- Sensor + — One wire from floor sensor probe
- Sensor - — Other wire from floor sensor probe
Important: Floor sensor wires are low voltage and must stay away from power wiring. Don't bundle them together.
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Ground Connection
Your thermostat includes a ground screw for safety grounding.
- Connect the bare copper or green ground wire from your circuit breaker to this screw
- Ensure the connection is tight
- Do not skip this step — proper grounding is essential for safety
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Common Wiring Mistakes
Mistake #1: Swapping LINE and LOAD
The problem: If you connect your LINE wires (from the breaker) to the LOAD terminals instead of the LINE terminals, your thermostat will not power on. The faceplate will not illuminate, and the system won't respond.
How to avoid it: Remember:
- LINE = power coming in from the breaker
- LOAD = power going out to the heater
Double-check your connections before turning on the breaker.
Mistake #2: Mixing 120V and 240V Wiring
The problem: Connecting a 240V circuit to a thermostat designed for 120V (or vice versa) will damage the device and create a fire hazard.
How to avoid it: Use a voltmeter to confirm your circuit voltage before making any connections. See our Pre-Installation Checklist for voltage verification steps.
Mistake #3: Connecting Sensor Wires to Power Terminals
The problem: Floor sensor wires are low-voltage. Connecting them to LINE or LOAD terminals can damage the sensor and thermostat.
How to avoid it: Keep sensor wires separate. They connect to dedicated Sensor + and Sensor - terminals only.
Mistake #4: Skipping the Ground Wire
The problem: A missing ground connection reduces electrical safety and may prevent proper GFCI function.
How to avoid it: Always connect the ground wire from your breaker to the ground screw on your thermostat.
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Wiring Diagrams
120V Single-Pole Circuit
Breaker (120V) ├─ Hot (L1) → LINE (L1) ├─ Neutral (N) → LINE (L2/N) └─ Ground → Ground Screw
Thermostat ├─ LOAD → Floor Heater ├─ Sensor +/- → Floor Sensor
240V Double-Pole Circuit
Breaker (240V) ├─ Hot 1 (L1) → LINE (L1) ├─ Hot 2 (L2) → LINE (L2) └─ Ground → Ground Screw
Thermostat ├─ LOAD (L1 + L2) → Floor Heater ├─ Sensor +/- → Floor Sensor
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Verification Checklist
Before turning on the breaker:
- [ ] LINE terminals connect to breaker wires
- [ ] LOAD terminals connect to floor heating system
- [ ] Sensor wires connect to Sensor +/- terminals only
- [ ] Ground wire is connected and tight
- [ ] All wires are properly stripped (about 3/4 inch)
- [ ] No bare wire is exposed outside the terminals
- [ ] Thermostat is secure in the wall box
- [ ] You've double-checked voltage matches your circuit
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After Installation
Once everything is connected:
- Turn on the breaker — The faceplate should illuminate
- Verify the display — You should see the current temperature
- Test LOAD power — After setup, verify your floor heater turns on when you increase the temperature
- Check sensor reading — The app should show floor temperature from your sensor
If the faceplate doesn't illuminate, check:
- Are LINE and LOAD wires in the correct terminals?
- Is the breaker actually on?
- Is there a complete power connection?
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Need Help?
If you're unsure about any wiring connections, stop and consult a licensed electrician:
Email: install@getmysa.com
It's better to ask than to risk damaging equipment or creating a safety hazard.