What is an NEC code-compliant way to install a 15A 120V dimmer switch --> driver --> led strip set up that enables the driver to be concealed or out of view but accessible for an in-wall lighting effect similar to below:

LED Inlay in drywall

The switch is to be close to the wall in which the LED strip and channel is embedded. Can the driver be located elsewhere in a cool/clean environment or inside some kind of junction box with the low-voltage connection run back to the LED strip? Since you cannot enclose electrical devices inside a wall cavity, how does a professional electrician conceal the driver while still being able to control the light via switch?

  • Couldn't the LED driver simply share a junction box with the switch, provided physical and Code fill limits are obeyed? – ThreePhaseEel Sep 3 '19 at 3:20
  • 1
    I think the issue may be the physical size of the driver. I'm thinking these staged areas must use a centralized power distribution hub/rack/shelf/plywood with screws/etc. in side a utility closet or near the breaker, run the supply to the dimmer switch, back to the driver near the breaker and then run a low voltage run to the light fixture? From what I've seen from the manufacturer: lightology.com/index.php?module=prod_detail&prod_id=356361 they use a nail-in junction box but don't address where the driver is placed. – 2and2IS5 Sep 3 '19 at 3:28

Eek! Don't use a 120V dimmer "switch" to drive low voltage LEDs.

In the 120VAC world, the scheme for dimming is an extremely hanky-janky hack, which was only made to work with incandescents. LEDs are immune to it. Dimmable LEDs need a microcomputer onboard to "outsmart" the janky dimmer scheme, reverse-engineer what the dimmer is trying to do, and then set dimming to that level. It's a true Rube Goldberg contraption already. Now try to add AC dimming a low voltage driver, and you have a totally unworkable train wreck.

In the 12 VDC world, LED dimming is blissfully easy. You make constant 12V, then you take that to an electronic "PWM" dimmer. This is an elegant method that plays to LED's strengths. It scales infinitely (you could dim a whole stadium using this method), you can carry dimming long distances as a signal, and then power each bank of lights locally, responding to the dimming command. You can have any dim level possible, limited only by the resolution of the dimmer. You can even "dim" RGBW, meaning select any color you want.

So yeah. Do your dimming on the 12V side. Also, it's low-voltage, so the easy low-voltage wiring rules apply.

So yeah. Stick the 120v-12V driver in the basement, and bring 12V up to the switch and/or lights. You could even put a battery there and replace the driver with a charger, along with a solar panel and charge controller. Then the lights would work during outages!

There are two ways to go about it.

Power to dimmer -> power onward to LEDs

Pretty straightforward: bring 12V to the switch, dim it, then send 12V (dimmed) to the lamps proper.

Signal to dimmer -> separate amplifiers driving LEDs

In this case, you send 12V +/- to the dimmer, and get "dim" (-) back as a signal (so 3-wires, low current; thermostat wire is fine).

Separately, you send to a basement amplifier:

  • 12V +/- power supply
  • the "dim" signal (-, and the dimmer's + also if this is a different power supply) as the signal input to the amplifier.
  • Some number of LEDs on the output of the amplifier

This can be repeated for as many [power supply]/amplifier/LED sets that you wish to drive.

If you want to do this with RGB, then the dimmer will output three "-" wires (and one + if you're talking to a different power supply or driving LEDs directly). The LEDs will take 4 wires: R G B and common.

If you want to do this with RGBW, then the dimmer outputs 4 "-" wires (and one "+"). LEDs will take 5 wires: R G B, W and common.

  • Thank you Harper. I will do what you suggested with the 120v --> 12V conversion and then run that up to the switch and then on to the lights. Is "to code" to enclose the transformer into a metal enclosure next to/near the breaker to keep it clean and centralized? – 2and2IS5 Sep 3 '19 at 4:23
  • 1
    @2and2IS5 That's fine, although 12 volts is very sensitive to voltage drop, so I would install it as close as practicable to the lights proper. Watch your voltage drop calculations! – Harper - Reinstate Monica Sep 3 '19 at 4:53
  • wouldn't 120v to the switch, 120v switch to an outlet inside a cabinet (bathroom vanity) and then the driver plugged into the 120v switched outlet, and then low volt from the driver to the leds be the way to go? – Fresh Codemonger Sep 3 '19 at 7:12
  • 3
    @FreshCodemonger ... No, because he wants dimming. Well, Maybe. You could ignore the dimmer/switch, run 120V to the cabinet, have the 12V power supply and an amplifier there, then run some 8-wire thermostat wire from there to the dimmer/switch. 8 for if you ever want to upgrade to RGBW. Two wires would be 12V supply and the other two would be PWM from dimmer to amplifier. You'd use the PWM dimmer output as signal to control the amp, not as power to drive LEDs directly. – Harper - Reinstate Monica Sep 3 '19 at 7:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.