Control Switch Wiring for a In-Line Exhaust Fan Low Voltage Control Switch Wiring for an In-Line Exhaust Fan Greg, this is a great question and the person who installed this in-line bathroom exhaust fan had a very good idea, as long as the exhaust fan is rated large enough for the square footage and required air exchanges of both bathrooms. The low voltage control wiring is relatively simple. Exhaust Fan Wiring Diagram (Fan Timer Switch) Exhaust Fan Wiring Diagram (with Fan Timer) This exhaust fan or bathroom fan wiring configuration uses a fan timer switch along with a separate switch for controlling the built-in light. This is an excellent way to make sure the fan automatically kicks off after 20 or 30 minutes or whatever time you set. Auto Fan Control System™ Installation, Operation, and PDF fileInstallation, Operation, and Maintenance Instructions - 1 or 3 phase from control panel to fans (see wiring diagram.) - *1 or 3 phase power (Note: The exhaust fan will exhaust some air while rotating backward. You must check the direction arrow on the fan. How to Construct Wiring Diagrams | Industrial Controls A damper is to open and when it is opened, an exhaust fan will turn on. With the two preceding conditions met, an indicator lamp will light. The system will all be low voltage to save on wiring costs. We now have the information to begin a wiring diagram.