240V baseboard heater with no neutral

Hi, I have a 240V in-wall heater controlled by a single pole dial thermostat…both L and N are 120V so 240V total.

I’ve been doing a ton of research and would like some validation/suggestions to make it smart.

I’m thinking of using a Shelly mini R3 with S-mate…would that work?

I found a diagram online of another possible solution. I’m wondering if this will allow me to use the old dial thermostat to trigger the heater as well. I believe the device is a Sonoff mini, but not sure what model as I’d want it to handle at least 15A.

Any help would be appreciated!

Here is what my current setup looks like

This is a non-sequitur. N should be zero.
What country are you in?
Is the thermostat a separate device or is it physically part of the heater?
A link to the heater model would help a lot.

Your description appears incomplete. Here is how 240V is typically supplied in a US home:


Don’t put a mini on a 15 amp circuit. 10amp rating it has is pushing it as is.

A switch capable of switching at LEAST 15 amp at 240 is what you sound like you need, Don’t get too hung up on the L and N designations, nothing is ground referenced.

Now what I said there is pretty basic Electrician speak. It any of that confused you or you are not sure what I said,
PLEASE get a licensed Electrician to advise you or better yet do it for you so to do not get hurt…


:warning: DANGER OF ELECTROCUTION :warning:

If your device connects to mains electricity (AC power) there is danger of electrocution if not installed properly. If you don’t know how to install it, please call an electrician.

Beware: certain countries prohibit installation without a licensed electrician present

Remember: SAFETY FIRST. It is not worth the risk to yourself, your family and your home if you don’t know exactly what you are doing. Never tinker or try to flash a device using the serial programming interface while it is connected to MAINS ELECTRICITY (AC power).

I’m in the USA. I shouldn’t have said L and N, maybe L1 and L2 is more appropriate. The thermostat is separate and single pole. The breaker is 240v with 2 live 120v wires and a ground. One line goes directly to the heater the other passes through the thermostat and to the heater.

Yeah I wanted at least 15A, would a Shelly Plus 1PM UL work? The Shelly mini r3 that I mentioned can also handle up to 16A.

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If you use a relay at the rated power for continuous periods, it will fail. You need a contactor for high currents.

Who installed the heater? From your sketchy description, I don’t think it would be up to code. Switching only one leg of a 220V circuit would definitely fail a code inspection.

I would really need to see a more complete schematic. It doesn’t have to be pretty. Just draw it on paper and scan it. Specifically what wires go where. From the breaker, through the switch box with the thermostat, then to the heater.