Currently I have 4 small low voltage transformers connected to 4 circuits of low voltage yard lights. They are under my deck, and I turn then on and off using switches above the deck.

I want to consolidate those transformers into one transformer.


My question is how do I use these switches to turn lights on and off from the deck.

I would like to use the same switches from the old transformers to do this.

It would be impractical to have to crawl under the deck to turn the lights on and off.

Should I connect the low voltage light wires to the switches, and then run wire from the switches to the transformer for each light circuit. I will have to leave the transformer in the ON state all the time.

What is the best way to do this? Any help would be appreciated. Thank you,

  • 2
    If it ain't broke, why are you spending perfectly good money to "fix" it? Sounds like you have a working set-up now - for what reason do you "want to consolidate" the 4 transformers (you already own, and can switch off) into one you don't already own that also requires re-wiring your switches and wasting power to keep it on all the time??
    – Ecnerwal
    Aug 9, 2021 at 18:32
  • 1
    Seems to me that a more logical question would be "I've got 4 sets of lights controlled by 1 transformer/switch and I want to be able to switch them independently, how do I do that?" Having individual control does seem to make more sense, and it seems you want to maintain that. What is the purpose of switching to a single transformer instead of the 4 individual ones?
    – FreeMan
    Aug 9, 2021 at 18:36
  • How much re-wiring are you willing to do? Is "a lot" OK? Aug 9, 2021 at 18:42
  • One of the transformers is failing. They are over 20 years old. Wires are coming loose. They need to be replaced. Also under the deck mess of wires. Just wanted to simplify. Thanks
    – RLM
    Aug 9, 2021 at 18:44
  • I know product recommendations are OT here, but I have a toroidal core transformer from Volt Lighting and it's awesome. Mine has 2 independent circuits built in. I gather that you want to continue to be able to control your 4 "zones" of outdoor lighting independently. If so you'll obviously need to move the switch connections between output (low voltage side) of the new transformer and the lamps. That transformer will draw very little power if none of the lights are on, so it being "on" all the time is not a worry. You'll have some re-wiring to do, but it sounds like it's time for that anyway Aug 9, 2021 at 19:12

1 Answer 1


Doing it right will be somewhat complex.

The transformer (300 Watts) puts out 20 or 25 Amps at 15 or 12 Volts AC, so typical 15A switches are not really suitable, unless you split it down through 15A breakers or fuses before the switches. The built-in breaker is 25A.

While perhaps none your 4 lighting loads may be more than 15A individually, the fault current in the case of a short will be the full power available from the transformer.

At least it's not DC - that's harder to find good switches for, though they do exist.

It's not particularly clear that "one transformer to drive them all" will result in any reduction/simplification of "wires under the deck" given that you'll need to run wires from the transformer, to the switches, back to the lights. Depending how the prior work was done, you may be able to clean up a bunch, or you may just rip it out and find yourself pretty much as complex as it was before, if somewhat differently.

TLDR: You almost certainly cannot re-use your existing switches (at least without adding MORE complexity, such as using the switches to control high-current relays that control the lighting circuits on the low-voltage side, so the current the switches are seeing is within their limits; or adding 4 circuit breakers on the low-voltage side to limit the current each switch sees that way.)

  • Will this work to connect 3 low voltage cables to 1 switch wire?
    – RLM
    Aug 9, 2021 at 21:03
  • With adequate work on your part, I suppose it can, while being 585 volts and 20A of overkill in one direction, and requiring a bunch of jumpers to do the job in the other. A 15 cent wire nut, used correctly, will do the same job - you can even buy a nice box to house it neatly with the money you save.
    – Ecnerwal
    Aug 9, 2021 at 21:12

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