Turn off the breaker and verify power is off before touching any wires when installing a bathroom exhaust fan with motion and humidity sensors.

Start by confirming you have the correct replacement fan and that its sensor functions are compatible with your existing wiring and switch type. Remove the old fan and note how the hot, neutral, and ground were connected in the junction box so you can restore equivalent connections. After turning off the circuit breaker, test each wire with a non contact voltage detector and then with a two pole tester if available to ensure there is truly no live voltage present. Use a cable connector to secure the nonmetallic sheathed cable where it enters the junction box and strip conductors to the length specified by the fan and connector manufacturers. Use Wago lever wire connectors sized for the conductor gauge to join like conductors: all neutrals together, all grounds together, and the hot feed to the fan hot and to the sensor hot lead as required. Fold wires neatly into the box without excess twisting so covers seat flat and recheck that every connection is tight by giving gentle tugs on each conductor before restoring power.

A common mistake is assuming the light switch feed is the only hot conductor which can leave a second always hot feed accidentally tied and energizing the box, so identify all hot conductors and separate switched hots from constant hots and mark them with tape if needed; then connect the sensor hot only to the intended switched hot. Another error is using backstab or loose wire connectors which can overheat, so use rated lever connectors or properly filled twist on wire connectors and verify pull out strength before finishing the job. People also neglect grounding the fan and sensor which can create shock risk, so bond all bare or green grounding conductors together and attach the pigtail to the fan grounding screw and to the metal box if present.

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