I have about 80ft of exterior stairs with two landings to which I want to add three zones of low-voltage lights. I would like a 3-way switch controlling each zone at the top and the bottom of the zone. I believe I could use one transformer and run low-voltage wire to all my switches however, I am having a hard time finding appropriate exterior switches and the equivalent of 3-wire wet-location low voltage wire.

My 120V brain says to just use UF-B 120V wiring and wet location switches/boxes that then feed three separate GFCI outlets into which I plug three separate transformers. The expensive part of the project are the lights so paying more for UF-B 14/3 or 12/3, for instance, appears nominal.

I'm using 12guage and a 20amp GFCI breaker wire in the example in case I need to use the outlet for electrical tools in the future. Other than having to buy three transformers instead of one, what are the benefits of a all low-voltage system over what I am proposing?

This is the only DC wall switch I can find: Leviton 12021-2I (SPST)

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  • 1
    What is the wattage of the lighting and how many? Hopefully you are using LED lights. Why do you want 3 zones? Ambiance? Appearance? If LED, you could easily run it all at once on a single transformer of sufficient capacity. Also LED would allow you to run MUCH LESS EXPENSIVE wiring. – George Anderson Oct 11 '20 at 14:34
  • Yeah, how many watts of lighting are we talking here? – ThreePhaseEel Oct 11 '20 at 14:41
  • Fifteen to eighteen 2W lights in each zone roughly. This is primarily stairway lighting. This is a secondary residence so I don't it on every "dusk to dawn" as it will just be used occasionally. LED. Zoned as I want to be able to turn on/off sections of stairs as you go up/down. – drjrt Oct 11 '20 at 14:54
  • @drjrt -- what voltage are you planning to use for the low-voltage side of the system? – ThreePhaseEel Oct 11 '20 at 17:36
  • The lights I chose were 12V – drjrt Oct 11 '20 at 18:07

I'd use relays for this

The simplest way to get out of this jam without throwing a bunch of lighting transformers at it would be to use single-pole/single-throw switches to switch on and off SPDT relays that control the lighting loads, as SPDT relay contacts can be wired in the same fashion as 3-way switches. For the switches, you can use Leviton 56021s with Bell 5123 (single) and 5127 (double) weatherproof covers; you have a couple options for relays, though. If you have space around where you're installing the switches, you can thread Functional Devices RIBU1C-N4 relays into hubs on the switch boxes; an alternative approach would be to use AP&C PAM-4 relays mounted inside the boxes, but this requires a fair bit of box real estate at each switch location. Both of these relays are rated for switching significant resistive load at 28VDC (7A for the PAM-4, 10A for the RIBU1C-N4), so 3A of LED lighting shouldn't be a significant challenge.

  • I started looking for SPDT (ON-NONE-ON) rocker switches for DCV thinking I could embed them in some type of plate but even that has been hard to find. Looks like relays. Functional Devices RIBU1C-N4 relays should match up with the threads on standard 3/4" water proof boxes? Also, this would work with my two 2-wire supply to each box; the extra wire would provide neutral for relay? I need to schematic this out.... – drjrt Oct 12 '20 at 20:52
  • @drjrt -- you'll probably want to use THHN in PVC conduit for the runs for this circuit just so you can get the wires you need without fretting about what UF cable configs are available. I haven't tried threading a RIBU1C-N4 into a hub on a Bell box, but I think it should fit? (You may have to do a bit of experimenting) – ThreePhaseEel Oct 13 '20 at 0:54

Since it is low voltage, you could do things that are not OK with mains voltage, such as running 2 2-wire cables you can easily source (wire-tied together) where you can't easily source 3-wire cable. You could also use 3-wire UF-B as overqualified low-voltage cable. It might confuse the next person to see it, but it would be perfectly safe/adequate.

Wet-location switch boxes that are set up to operate a "normal" switch protected inside the box exist, and AC/DC rated switches also exist, though they are harder to find than AC-Only switches. I have not throughly investigated sources for wet-location low-voltage DC-only 3-ways at this point. Boating suppliers might be a good place to look, for instance.

If going with the 120V approach, I'll always suggest conduit as superior to UF cable.

  • Well, there's the rub. I simply cannot find SPDT DC rated switches after several hours on my good friend Google. – drjrt Oct 11 '20 at 15:52
  • Remember that you can also use half of a DPDT. The extra pole won't cost you extra, normally. And that google can be less than utterly helpful in sending you to the right places; they like to misdirect your search to their special friends who give them money. Mouser electronics lists multiple in-stock waterproof DC toggle switches, for one. Not shockingly, so does West Marine. Digi-Key and Newark electronics probably also have them (from the electronic parts side), as would any other boating supplier. Industrial controls is another direction to look... – Ecnerwal Oct 11 '20 at 16:14
  • Well, I can find many toggle switches but I'm looking for something that will have the look and feel of a traditional switch – drjrt Oct 11 '20 at 16:35
  • Another 1-1/2 hours searching. No SPDT or DPDT DC rated wall switches to be found. Leviton makes a few DC rated but the only DT is momentary contact. Sigh. – drjrt Oct 11 '20 at 17:32

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