I have a custom built new construction home, but I was not involved with the build process, so I don't know the thought behind some of the equipment decisions.

I am an engineer, so curiosity has me exploring some of the technical details of my home, I am not having any issues with the electrical system.

Near the main electrical panels, there are three low voltage DC power supplies. I am trying to understand what they are used for.

Using a multimeter, I was able to determine that they are powered via a circuit breaker in the main panel labeled "Low Voltage System". Turning this breaker off doesn't seem to make anything in my home stop functioning (Lighting, smoke alarms, HVAC all work normally with this breaker turned off).

They are not involved with the door bell or HVAC equipment (As there are standard AC transformers for this equipment).

My home is equipped with a generator transfer switch (See: Using portable generator with transfer switch), could these somehow be involved with that?

Does anyone know what these power supplies are used for?

Main Electrical Panels:
Main Electrical Panels

Cover Removed from power supply:
Low voltage power supply

  • That's not a transformer. That's a power supply. Transformers make AC voltage. Power supplies make a bunch of other stuff. This one is 12 volts DC, but it's injecting power into the AC mains wired through a single conduit, so the low voltage is mixed with the mains. That means everything it's connected to must be wired like AC mains - it can't switch over to thermostat wire or something like that. Do you have dimming? 0-10V dimming perhaps? Sep 21, 2020 at 20:26
  • We have no dimming for any of the lighting in the home. I have updated post change from transformer to power supply, thanks for the clarification.
    – cyclops
    Sep 21, 2020 at 20:38
  • 2
    Other than the obvious "ask the builder" could be something that's battery-backed (alarm/smoke alarm) though those are more commonly supplied at/near the "main panel" for the alarm system. Possibly DC outdoor lighting you might not have thought to check, or known was there?
    – Ecnerwal
    Sep 21, 2020 at 20:43
  • 2
    google search says it is an LED driver. You must have some kind of led lights - landscaping? soffit? staircase? under cabinet? - that stop working if the breaker is off for it. Sep 21, 2020 at 21:06
  • That it’s 12v I would look to see if your doorbell or furnace are connected these are normally 24v and use less expensive transformers. It could also be for some LED lighting 3 amps is not a lot at 12v but would be enough for some LED lighting at steps or entrances video or surveillance cameras?
    – Ed Beal
    Sep 22, 2020 at 1:50

1 Answer 1


After additional searching, I found that these power supplies are used for the full home audio system using similar (But not the same) wire as each speaker uses. The system was never fully installed, so I didn't notice it before.

Currently all of the speakers and outputs of these power supplies are just left un-terminated in giant spool of wire in the utility room. I don't believe this to be code compliant as the low voltage and high voltage wire share a single conduit.


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