It seems there are a couple ways to do this, but I haven't seen the exact solution I'm looking at so I wanted to check with the community on this. I have a 4KW patio heater I'd like to control with a countdown to avoid leaving it on for days.

An out of the box solution doesn't seem to exist, so I'm looking at controlling a 40A contactor with a countdown timer. I've seen solutions for a mechanical spring wound timer with a contactor, and a digital timer with a relay, but I'd like to use the digital timer with the contactor.

I figure it's easiest to just have everything at 240V, so I've speced a 240V contactor with coil volts at 240 as well, to avoid running a separate line just for the switch.

Timer rated 240V

Contactor 240V/ 240V coil

enter image description here

If the picture isn't quite clear L2 connects directly to A2 on the coil.

My understanding is that the mechanical spring wound timer, doesn't require a neutral.

The digital timer does require a neutral, so I can power it off of one leg coming in, and tie the neutral together. But this leaves 120V to the switch and 240V in the box, so I would need a common-trip 2pole breaker to power the circuit from the panel.

Anything else I'm missing here? Appreciate the help. This will be installed in a NEMA 4X box and I'll tie all the grounds to a grounding bar.

I'm getting conflicting solutions for low voltage solutions. What if I just used this timer? It's spring wound, which I don't love, but it's UL listed in the documentation from the supplier. And it's just one part for easy installation. Rated to 28A which should be sufficient for my 4000W heater.

If I were to wire it up with 120V. Would this be the right way to go? One side of the coil gets the white neutral wire, the other side gets a red switched hot wire from the switch. This seems to be the most straight forward in my head. Admittedly, and clearly, I don't have a ton of experience with 240V hence my confusion around neutral.

enter image description here

  • 1
    A 40A contactor at 240V is 9.6 KW (7.68 derated). You need 21A or greater (derated) for 4KW @240v, so likely a 25A contactor.
    – Ecnerwal
    Commented Mar 10, 2023 at 16:17
  • What kind of breaker is powering your heater? What type of cable runs from the breaker to the heater?
    – longneck
    Commented Mar 10, 2023 at 16:18
  • 1
    I would recommend a common-trip 2-pole breaker (a.k.a., a standard double breaker) anyway. But as far as neutral - there is actually no magic that an electronic timer (or motion sensor or smart switch) needs "neutral". It needs power, which means a complete circuit. In a 120V setting that means "hot" + "neutral", so that is where "need neutral for a smart switch" comes from. In a 240V setting that means "both hots" - and if finding a 240V timer (assuming the cost is reasonable) saves you running a neutral a long ways, it is worth it. Commented Mar 10, 2023 at 16:18
  • 1
    This is all a new installation. The junction box with the switches will be about 30 feet away from the main breaker panel. Specing a 30A breaker and the cable size to go with it. So running an extra 120V circuit in the same conduit is definitely doable, I was just wondering if I had to run the separate neutral.
    – ABethea
    Commented Mar 10, 2023 at 16:31
  • 1
    The 240V electronic switch does not need a third conductor ("neutral") if the cable routing is from the panel to the switch and then to the contactor. However if it's cabled as a switch loop it needs a /3 cable. The third wire is not strictly a "neutral", but it's an unswitched current path for the switch's power needs from the pole opposite to the switched one.
    – jay613
    Commented Mar 10, 2023 at 16:38

4 Answers 4


For a slightly different approach, mount a contactor with a 24V coil in the vicinity of your breaker panel and run thermostat wire (or its equivalent) to a spring-wound timer on the patio. With the human interface at 24V you'll eliminate any outdoor shock hazard. The 24V transformer can be mounted adjacent to the contactor. No neutral would be needed past the contactor and its transformer.

EDIT: With your wife's stated preference for a digital timer, Chris O points out that 24V digital timers are available. So you can have the best of both worlds.

  • My wife likes the idea of a digital timer rather than spring wound. I do like the idea of lower voltage.
    – ABethea
    Commented Mar 10, 2023 at 16:53
  • I was hoping to throw everything into one box, but now it seems, having one box for 24V and one box for 240V would make a lot of sense.
    – ABethea
    Commented Mar 10, 2023 at 17:05
  • 1
    So now that I'm lookign at 24 volt controls. I could have a 24V box with the switch and another box with 240V running a contactor like this. grainger.com/product/EATON-Definite-Purpose-Magnetic-49C072 Would just need a transformer and run the switch off an existing circuit. Heck, I could even put it inside with a bit of extra effort.
    – ABethea
    Commented Mar 10, 2023 at 17:11
  • @ABethea Just a note: contactors make a loud clack when they engage and some (most?) will hum noticeably. I mentioned locating it near the breaker panel; noise is one good reason not to have it in your main living space.
    – MTA
    Commented Mar 10, 2023 at 17:19
  • I do not think you can use thermostat wire with that 24V contactor. The two sides are not separated within their junction box, so once the 24V wire exits the box it has to be to high voltage standard, ie cannot be thermostat wire. If it's all inside one box you don't have a problem to solve but then it may as well be 120V on the switch side. There MAY be a way to install and mount the contactor so the 24V side is isolated. Worth researching?
    – jay613
    Commented Mar 10, 2023 at 17:43

I've done exactly this with a water heater. (setting aside the fact that you chose a specific purpose contactor). I used the existing 240V circuit that did not have neutral. Your "spring-wound timer" drawing looks correct to me, that's what I did.

Mind you, I used a normal spring-wound timer. It simplified the installation. If you lack wrists or are a millennial, then perhaps you don't have that option. In that case I would point out that the switch is rated for 120-277 volts, and the 277V world is actually 480V 3-phase in "wye" configuration, with 277V from any phase to neutral.

So for use in a 240V context, when they say "neutral" they really mean "L2".
Your use of black & black to the timer switch there is correct; since the two wires are "L1 always-hot" & "L1 switched-hot". They are both L1. I prefer to reserve red for L2. Thus the "smart timer switch" diagram is oddball and that's why you're having trouble visualising "L2 as substitute for neutral".

I mean if you want to throw a neutral wire in the conduit go for it... I could've done that, I just didn't bother. Also I'm a bit cheap and wasn't willing to use that much #10 white. And I have a bunch of 30A single-pole breakers bought in error; they have no useful use except travel trailers. By not running neutral, I can handle-tie two of them. With neutral I would need to buy a 2-pole breaker.


Here is how I would try to approach this. Other answers are good but each presents problems that I would prefer not to solve. I think this one is easier.

[Updated, now that you've described the layout] Since you're replacing your panel now, and the switch location is outdoors not far from the panel, we'll use three new GFCI breakers and conduit to the switch.

  • Choose a location on a wall near the heater for an exterior-rated junction box with a 3-gang front that can house a contactor and switch.
  • In the panel install a duplex GFI 30A breaker for the heater and a single 20A GFI breaker for the switch and a bonus outlet.
  • Run PVC conduit from the panel to the switch location. If you don't mind seeing it on the wall, that would be easiest, otherwise bury it. 1/2 inch conduit is enough for this but I would install 3/4 because, why not.
  • To the new box, pull a black and red #10, and black, white, green #12.
  • Run another conduit from the box to the heater with red, black #10 and green #12.
  • Buy a contactor with 120V coil voltage, and buy a 120V timer or smart switch that provides whatever functions you'll enjoy. By going with 120V you get lots of choices.
  • Connect the switch and contactor according to the last diagram you added to the question, which is correct. If you're using a contactor with spade connectors, make sure to buy connectors with appropriate current rating and to use a correct crimping tool, not pliers.
  • Since you have the GFI breaker and 120V circuit available, add an outlet to the box. All you need is a GFI sticker.
  • Cover the whole thing with a wet-in-use cover.

The timer may not be exterior rated but with a proper enclosure and cover I'd go with it anyway.

Since you have the new 120V circuit you could also extend the #12 wiring up to the ceiling through the same conduit and from there add some lights. If you plan to do that, I would use one two-gang box for the contactor and outlet, and another for the heater switch and light switch.

  • 1
    My main panel is on the outside on the side of my house. I'm actually having it replaced right now. The patio is on the back of my house about 30 feet away. So adding another breaker or pulling more wire is very easy. I'm just trying to do this the right way and it seems people have different opinions on the matter. My plan was to put the whole thing in an exterior rated enclosure on the side of the house. I coudl go with this contactor grainger.com/product/DAYTON-Definite-Purpose-Magnetic-6GNZ2 and just about any 120V switch/timer.
    – ABethea
    Commented Mar 10, 2023 at 21:48
  • I made revisions to this answer based on new information in the question and comments including the above one.
    – jay613
    Commented Mar 11, 2023 at 14:41
  • Thanks for your help here. I feel much more confident in this. Just curious about one more thing. If I were to run the switch (120V) into the house, instead of having them in the box. Are there any issues with that? Same gauge wires and everything, but run a new switch off an existing plug in the house, then run the cable outside in a conduit to the box with the contactor in it. I like the idea of physically isolating people from the 240V box, but curious if it's acceptable to run 120V wire from a box with 240V in it. I would assume yes.
    – ABethea
    Commented Mar 11, 2023 at 19:55
  • "Protecting people from 240V" isn't really a thing. Usually, especially outdoors, danger is from live to ground. There's 120V from either live wire to ground. To be exposed to 240V, a person would have to touch each of the two live wires connected to the contactor without first popping the GFI breaker or becoming electrocuted by "only" 120V, which is more than enough. IF they somehow manage to do this, it won't be because the timer switch is in the same box! What you want to protect them from is becoming a path for ANY live wire to ground. And that is what the GFI breakers do. [1/2]
    – jay613
    Commented Mar 11, 2023 at 20:39
  • [2/2] IMO you should guide yourself with what's functional and convenient. If it makes sense to put the switch indoors, then yes you can power from an existing circuit and don't need GFI. Then you just run a 12/2 wire (or 14/2 if it's a 15A circuit) from there out to the contactor (the switched live and neutral, just as in your pic). Some additional minor issues with routing of that wire from inside to outside, with details that depend on layout and access and that are covered extensively in other questions. In the answer I took advantage of the easy layout of a conduit from panel to box.
    – jay613
    Commented Mar 11, 2023 at 20:45

Building on MTA's answer, 24V is definitely the way to go.

However, once you're settled on low-volt controls, there is no need to go spring-wound if your wife isn't into the old-timey rotary switch. There are lots of other options for 24V controls, such as this digital one from Legrand. Fits a Decora wall plate and standard 1-gang mud ring so it blends in nicely with existing switches.

Not a specific product recommendation - that's just the first one I found.

enter image description here


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.