I plan to mount floodlights on the back of my house. I have a Romex running through the wall between the mounting point and my electrical box. I want to test my floodlight before I go to the effort of getting on a ladder and installing it - I want to make sure it is bright enough and dims appropriately. Next to my back door (my testing location) I have a normal 1-gang, 2 socket outlet.

The floodlight itself is dumb. Just a bulb socket and the neutral/load/ground wires. I very easily took an extension cord, cut it in half*, plugged it into the outlet, and wired the other end to the floodlight. Viola - easily test the floodlight, it lights up, it's bright.

Now I want to test the Smart Dimmer in the circuit, to make sure it dims the way I want it to. The smart dimmer requires a neutral wire. The way I am thinking about this is along the lines of "I just need to get power to this wire..." and I have this second outlet so... Can I just cut another extension cord in half, plug it into the second outlet and wire one of the wires to the smart switch's neutral wire? If so, which of the two wires would I use, and how would I determine which one to use with a multimeter (to be absolutely certain the outlet isn't wired backwards or something)?

* I didn't actually do this, I had a plug I cut off something I was throwing away but I figured this description was more complicated than it needed to be.

  • Type of light will be helpful. Old style incandescent should just work. New style LEDs types need to be dimmer friendly.
    – crip659
    Jan 27, 2023 at 22:29
  • how would I determine which one to use with a multimeter (to be absolutely certain the outlet isn't wired backwards or something) I don't think anyone answered that part - easiest is with a 3-light tester; with a multimeter, just compare the two other wires to ground - ~120V hot to ground, ~0V neutral to ground. Jul 24, 2023 at 15:13

2 Answers 2


Use the extension cord you already have. Extension cord hot to smart switch supply hot.

Lamp hot to smart switch lamp hot/switched hot.

Both neutrals to smart switch neutral.

Safety first, don't get nailed. If you want to put that in a junction box, that'll help.


Connect the dimmer's neutral to the extension cord's neutral that you use for the flood lights neutral.

If the line/neutral is reversed, the dimmer may or may not work but you won't damage it. It's not like DC polarity.

To identify line from neutral you can use a contactless tester, a screwdriver style line voltage tester or a multimeter in AC mode. The testers will read nothing on the neutral but will positively identify the live. The multimeter (or a 2 wire voltage tester) will read near 0V between neutral and ground (copper/green), but 120V between line and ground. (It will also read 120V between line and neutral but that still doesn't tell you which is which.)

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