Electrical – How do we wire a new bathroom exhaust fan to our bathroom

electricalexhaust-fanswitchwiring

In our attic we have a junction box that has the power wire connected to a hallway ceiling light. Can we tap into that to get power to install a bathroom exhaust fan? We would be putting in a double rocker light switch in the bathroom (top switch would be for the vanity light and the bottom switch would be for the exhaust fan switch). How would we wire this?

Best Answer

There's several parts here

Can I tap into the junction box for power?

Yes, provided it's not overloaded with wires.

How do I wire it?

If I were you, I'd add a second junction box. You'll have

  • 2-line power from the existing box
  • 2-line cable run to your fan
  • 3-line cable run to the switch

Find the breaker to the box you want to tap into and turn it off. If it's 15A, buy 14 gauge wire (Romex is white), if it's 20A, buy 12 gauge (Romex is yellow). Be sure to clamp the cables if any box is metal.

Inside the new box, wire

  • All 3 white wires together
  • All the bare grounding wires together (run an extra one to your box grounding screw if the box is metal)
  • The incoming black wire from the other junction box to your 3-line black wire
  • The black wire going to your fan to the red wire

Inside the junction box for your switch, it sounds like you have an existing switch. If so

  • Break the tab on the side of your double-switch
  • Wire the old switch wire to one of the switches
  • Wire the new black and red to the other switch
  • Cap your new white wire with a wire nut
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