I bought a house with a low-voltage lighting system, where the switches have low-voltage wires that power relays that actually power the full-voltage lights. I want to find out if I can take advantage of all the low-voltage wiring to install a system that can integrate with home-automation systems. The relays are all centrally located, so I am hoping that a centrally located computer could do the work of the old relays.

I am assuming that I would have to replace all the switches and relays with something more compatible with computer I/O voltages or something like that, but I am not very proficient with electronics, which is why I am asking here.

A description of the system can be found here: https://www.kyleswitchplates.com/sierra-electric-low-voltage-lighting-info/

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Any ideas?

  • 1
    get an accurate schematic of how the switches and relays interact Jul 30, 2018 at 10:14
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    Sounds like a GE 12v relay system
    – Kris
    Jul 30, 2018 at 11:59
  • @ratchetfreak @Kris I just found this website selling replacement parts. Mine is the Sierra system. Looks like 24V relays, but I can double-check that with my multimeter. kyleswitchplates.com/sierra-electric-low-voltage-lighting-info Jul 30, 2018 at 13:47
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    I would suggest that you leave the relays and switches and simply use your own low voltage relays to control the existing relays. There are kits for computer activated relays.
    – Dan D.
    Jul 30, 2018 at 15:15
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    I would use MOSFETs to switch the existing relays; they wire up about the same as a low-voltage relay but don't use holding power, have no moving parts or heat, and are cheaper. If you're not an electronics whiz, they sell "solid state DC relays" that are essentially MOSFET modules.
    – dandavis
    Jul 30, 2018 at 16:28

2 Answers 2


I would use the system as it is and add a low voltage relay that the computer controls to fire the existing relay. With this method the existing switches would still be functional as an overide, one example might be similar to an arduino relay board using the arduino micro controller my grand son and I built a 12 channel Christmas light controller, in your case you use the relay to bypass the switch and pull in the larger relay using the existing low voltage control.

  • I want to be able to program my computer keep track of whether the light is already on or off. Can I just add a connection (with the appropriate resistor?) from the wire between the switch/relay and an IO port? Jul 30, 2018 at 19:21
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    There are several ways to track with the computer, some systems I use current transformers they produce a voltage when a wire going through the center of a coil causes a voltage output totally isolated from the branch circuit , another way depending on your relay is to use an unused set of contacts or possibly a aux contact set that follows the relay state, this can be powered by the controller, or use the low voltage side to watch a voltage. These are the common ways there are halleffect sesors that detect power but these may not work well depending on wiring.
    – Ed Beal
    Jul 30, 2018 at 20:33

That brings back memories! A friend had a similar system in his house growing up. This is know as a 3 wire low voltage system. Only way to integrate aditional control points(computer or aditional switch locations) is to extend the 3 wires that are connected to the switch. You will need 2 relays for momentary contact purpose. Red wire is to signal the relay to turn on. Black wire is to signal the relay to turn off. The third wire is the common power for both relays. With those wired to the normally open contacts of the relays then you just need to wire the relays to the computer and program it for momentary energizing of the requested relay(s).

  • If I understand correctly, you're saying that I need 2 new relays (one for "on" and one for "off") to send "on" and "off" signals to the existing relay, the same way that the switch sends those signals to the existing relay? Jul 30, 2018 at 19:36
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    That is correct. The switches send a low voltage pulse to the corresponding coil in the relay. You would need 2 relays , one for on and one for off. Keep in mind that the relay needed to control this low voltage control can be quite small. Probably circuit board size of small.
    – user68386
    Jul 30, 2018 at 19:52

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