Using a countdown timer to control a 40A 240V contactor

Question

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

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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.