Built a bathroom onto our office and need to run a switched line for bathroom ceiling light and exhaust fan. For simplicity's sake, looking to pull power source off the end of a line already on a switch. The already established line powers two ceiling lights in the office and I understand that this line needs to be switched on for power to go to bathroom. This is fine, nobody will be using the bathroom unless the office is in use anyway. Just want to know if this is okay. Thank you!

  • Can you post photos of the inside of the existing switch box please? Feb 12, 2020 at 2:35
  • can do that tomorrow. Thanks for responding. I can tell you that the light I'm planning on tying into only has the one hot wire, one neutral wire and the ground coming into it from the first light, if that helps! I was just planning on continuing the circuit.
    – Mark C
    Feb 12, 2020 at 2:51
  • Are you aiming to pull this from a light, or the switch? Feb 12, 2020 at 3:46
  • Pull from the light, the existing light in the office ceiling is adjacent to the new bathroom wall and for ease and simplicity, I want to just tie into that. I already have the bathroom light and vent wired to a new box and switch in the new wall. I have new wiring tied to the new switch and box running up the new wall into the dropped ceiling of the office. just need to connect it to power. Basically just continuing a circuit but with a switch in line to a circuit thats already switched. It's fine with me that both lines need to be powered on for the new light to work. Thanks again!
    – Mark C
    Feb 12, 2020 at 4:21
  • Just want to make sure this is safe and okay!
    – Mark C
    Feb 12, 2020 at 4:22

2 Answers 2


Electrical work should really be done by a licensed Electrical Contractor. Please only undertake DIY wiring if you REALLY understand what you are doing.

What you are suggesting is not ideal, and should be avoided if possible.
How are you planning to switch the new fittings? Sometimes, for example when retrofitting say an exhaust fan to a bathroom or WC, there is no access, and the only way is to tap into the light, generally using a pull-cord switch. Not ideal but sometimes unavoidable.

  • ThreePhaseEel.........I pulled the cover off of the existing switch box and saw instantly where you're going with this. I'm under such a time constraint before a preliminary inspection to open this office that I'm trying to shortcut things and forgot to think. ( doing the framing, drywall, spackling, plumbing , dropped ceiling, painting , etc...., myself, after working regular job all day. ) No need for photos. The switch IS powered by the light. Just one black wire to the switch and one whlte wire out from the switch along with the ground. I'll tie into the power source at the first light.
    – Mark C
    Feb 12, 2020 at 23:31
  • Thanks for bringing back down to earth. :-)
    – Mark C
    Feb 12, 2020 at 23:32

You can do that but when the switch in the office is turned off, it will also turn of the light and exhaust fan in the bathroom while in use.

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