# Control 12V LED circuit and 120V power supply from one switch

I want to have two switches (preferably in the same box) that control two separate runs of LED lights, both powered by a single Allanson power supply:

I plan to switch the lights by breaking the 12V negative leg of each light run (tell me if this is a bad idea).

I believe that when both LED light runs are off:

1. The power supply shouldn't be powered by the mains because it has no load and could be damaged
2. Even if point 1 is wrong, the power supply needlessly consumes power

Based on these assumptions, I want both switches to also switch the 120V hot powering the power supply. Therefore, the power supply should be off if BOTH switches are off, and on if EITHER switch is on.

What parts and wiring configuration is needed to accomplish this?

I'm in the United States.

I read this question which describes a double pole switch; however the research I've done gives me the strong impression having 120V and 12V in the same box is not permitted.

Edit: Local building codes prohibit low- and high-voltage from coexisting in the same box, even if both use conductors rated for the highest voltage. Now what?

• You don't need to switch the 12v side. Just switch the 120volt to the ballast. Then the ballast will not draw any power when the switch is off. Aug 16, 2017 at 15:42
• That would work if I only had one strip of lights I want to switch, but I have two, both powered by the same transformer. I'll edit the question a bit to make that point more clear. Aug 16, 2017 at 15:44
• But the o.o wants 2 separate strings of led's controlled by 1 transformer. Aug 16, 2017 at 15:45
• If they are in the same box, all wire has to be insulated for the higher voltage. So, you can't use cheap wire on the 12 volt side. Double pole switches would do what you want. A divider is not required by the Code until you have more than 300 volts between switches as with 2-277 volt switches on different phases. It's always a good idea though. Aug 16, 2017 at 15:53
• You would have to hook it up to a "Kill-a-Watt" type device and actually measure how much power it uses driving into no load. It may not be enough to care about. At 12 cents a KWH (a common power price in US/EU/UK), 1 watt run continuously costs 100 cents per year. Aug 16, 2017 at 22:04