Switch - Identifying Line vs. Load wires

Something that might help others who, like me, have line and load wires both colored black instead of one black and one brown:

  • The line wire is typically connected to the bottom terminal of the existing switch, and the load to the top (though I think this is already called out in the installation instructions).

  • If you want to confirm further, or if your box is empty, inside the outlet box at the back the line/incoming wire typically comes into the box from the bottom, and the load/outgoing wire typically enters from the top.

Hope this helps someone!

Don’t guess. You can get one of these and you can use it to identify the line connection. Load will not have any power if the switch is off. When in doubt, hire an electrician.



Yeah I don’t think the OP’s advice is wise either. I would check both lines with a multitester against ground, both before and after shutting off power at the main panel.

You could also just use a light bulb tester.