My wife has a fish tank in the living room. It requires continuous power for the pump/filter, and automatically controlled power for lights and a CO2 solenoid. Since water is nearby I'll be putting it on a GFCI circuit. My wife would also like to flip a switch to override the automatic schedule and turn on the lights; same for the CO2.

We currently have everything on an extension cord and a mechanical timer. I plan to replace that with a custom WiFi-enabled electronic gizmo and some proper receptacles.

Is the following an okay plan?

Mounted in three gang wall box behind the fish tank:

  • One duplex GFCI outlet (two receptacles). This will provide GFCI protection to everything as well as two always-on receptacles. 15A receptacles (20A feed through). Tamper resistant. LEVITON GFTR1-W
  • One duplex outlet (two receptacles) marked "controlled" on both receptacles. Hot tab broken. One will be for lights; the other for CO2 solenoid. 15A. Tamper resistant. LEVITON TBR15-S2W
  • One duplex combination toggle switch (two switches in one gang); both will be three-way. Each switch will switch one "controlled" receptacle between automatic control and always-on. 20A. LEVITON 5640-W

Wall box diagram: Wiring diagram

I'll tap into the existing outlet circuit in the room. Hand-wavy control circuitry will be mounted in the crawlspace below the floor.

Am I allowed to use three-way switches like this?

I know I'll need 12AWG wire. Will I need $$$ 12/4 (with ground) wiring to/from the control circuitry, or can I do that with two runs of 12/2 (with ground)?

As stated above I'm imagining the receptacles and switches (image above) living in an old work box in the interior wall behind the fish tank, and fishing wires through the wall down to some kind of enclosure between the floor joists where the control circuitry will be hardwired in.

The crawlspace below this floor is 5+ feet high, unfinished, and you access it by opening a trap door in a closet and climbing down a portable ladder that's usually there. I'll ask my AHJ, but I bet the control circuitry will be considered "accessible" since it doesn't require modifying the structure or removing drywall or anything like that, and also because there are already outlets (in the NEC sense of the word) down there (for well pump, sump pumps, water softener, etc).

We live in Michigan, USA. This is the other half to this question.

  • Of course the cheaper alternative would be a couple of COTS WiFi outlets on a GFCI circuit. But where's the fun in that? Jan 11 at 3:10
  • How do you plan to be able to override the controls to off for servicing? Jan 11 at 4:27
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    @MattThomas: " I'm a programmer by day". In that case, you may want to check out Home Assistant as a controller. If you plan to add more automation in the future it has a lot of advantages.
    – Orbit
    Jan 11 at 7:58
  • 2
    I'd give a vote to HA (Home Assistant) to control it and Shelly 1 relays (UL Listed) to make up your "3-way" switching options. A simple toggle switch, when wired with the Shelly 1 behind it will, with some very simple automation in HA will do everything you need. You can even manually override with the switch, then start a timer to automatically turn off again after a specified period of time so you don't forget to turn it off.
    – FreeMan
    Jan 11 at 14:00
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    Another way to do this, close to your idea where you have a wall switch without home automation but no 12/4 is a wireless ceiling fan and light controller such as this one. I respect your desire to learn, but I can tell you running 12/4 through your crawl space is NOT the part of it that will fill you with satisfaction.
    – jay613
    Jan 11 at 17:02

4 Answers 4


That looks impressively legit.

You cannot use dual 12/2 because currents must be balanced in each cable or conduit. This is AC we're dealing with, anything the power goes around becomes the core of a transformer. That stuff doesn't matter on DC. (if it's actually DC; PWM isn't DC quite.)

However, the fact that you want to use NM cable (Romex) tells me that both the switch box and the equipment box are mounted in the wall. (Because NM cable is NOT usable for any other purpose; it is definitely not extension cord).

As such, you might as well use conduit between the boxes. Smurf tube would be ok in the walls, EMT would be ok on the surface of the walls. Once the conduit is installed, you can use individual wires in the conduit - again with all wires in the conduit balanced so all power that goes out that way comes back that way.

I will NOT open the "can of worms" about whether the special equipment is UL Listed. If you need UL listed AC switching equipment that is controlled by a micro controller, there are loads of ways to stick a WiFi or Bluetooth shield on a Raspberry Pi or Arduino, and have it control UL-listed commodity plug-in smart appliance switches. Or BSR X-10 is a tried-and-true way of doing that.

  • Yes I imagine the whole shebang will be hardwired. I'd lean toward running wires in the interior wall. I'll keep smurf tube in mind if I use individual conductors. I'll talk with my AHJ about it, but my impression is as long as my control circuitry passes his inspection then to Insurance Company Inc. it's as good as being UL listed? Jan 11 at 14:15
  • "running wires in the interior wall" - Just to reiterate/clarify what Harper is saying: If stuff is inside the wall it must either be proper cable (e.g., Romex) or inside conduit. You can't have loose wires except in a junction box. Jan 11 at 15:12
  • @manassehkatz-Moving2Codidact I understand. Thank you for reiterating it. I guess my comment does sound like I'm confused about whether conduit is optional with individual conductors, but in reality I'm only confused about if smurf tube is optional (or if there are other kinds of conduit that you can fish inside a wall... it seems like EMT or PVC would be a lot more difficult). But that's a separate question :) Jan 11 at 16:47
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    Any kind of conduit will work. The suggestion of smurf tube was because since it is flexible it is generally the easiest to retrofit. If you don't mind tearing up the wall, EMT or PVC is fine. Jan 11 at 16:59
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    @Matt yes, don't let me deter you from using FMC if you prefer! My point is that conduit lets you use individual conductors, which solves the 4-wire problem nicely with room for expansion. Jan 11 at 20:46

If you want to take an approach very similar to the one you designed with a wall switch near the door but want to avoid running cable through the crawl space, buying expensive 12/4, and also don't want phone apps .... here's an option.

Follow your design almost exactly, but instead of the duplex switch use a wireless ceiling fan controller like this one.

enter image description here

Everything else about your design is identical. You still need a 3-gang box to accommodate the receiver. You wire it identically to your design, there just is no cable to the switch. You'll need to buy a 2+blank cover plate for the junction box it's in.

If you already have a 12/2 cable and switch in the wall you can keep that as a master power switch overriding the remote.


Yes, you will need 12/4 to that control box. Or alternatively, run conduit and individual wires.

The control box must be accessible. Not sure that the crawlspace counts. I'd try to find a way to mount it all either in or on the wall near the fish tank. Also, since that control box will be dealing with 120V power, it needs to be built to code. Meaning: no funny imported non-UL/ETL listed parts.

  • 1
    The crawlspace is 5+ feet tall and (obviously) unfinished; you access it by opening a trap door in a closet and climbing down a ladder. Worth it to ask my AHJ if the floor joists are "accessible"? Jan 11 at 3:35

I'd put the low/high voltage boundary over here, instead of over there

My solution to this problem would be to move the low voltage/high voltage boundary to this junction box using a hub mounted 24VAC transformer, such as a Functional Devices TR20VA004, and a pair of RIBTELS optoisolated enclosed relays with override switches and high/low separation. This lets you just run a 18/4 or 18/5 thermostat wire over to your fancy custom WiFi gizmo with just an Altronix VR1TM5 there to generate 5VDC from the 24VAC, and incorporates the override/disconnect functionality into the hardwiring with clear labels instead of requiring things to be unplugged from the rig to service them.

It does have the downside of not being quite as "tidy" as your proposed solution, due to the need to keep the RIBTELS and their override switches accessible, but one could hack the RIBTELS to move its override switch to the coverplate if one wished, which'd yield a reasonably neat way of doing things provided you could find a suitable filler for the hole in the box said switch leaves behind.

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