Easy DYI heavy-duty appliance (240v/20a) switch

I wanted to offer a quick report on a small DYI project I just finished in hopes that other folks in the community might find this useful.

I wanted to be able to control the power an A/C unit that takes 240v 20a input (NEMA 6-20 type plug). The few off-the shelf solutions I found (ELK9200, Intermatic CA3750 and Aeon ZW078) would’ve all involved heavy-duty wiring, which I wanted to avoid doing. Additionally, NEMA 6 plugs/receptacles seem to be expensive and hard to find.

I decided to take a dumb (non-connected) heavy duty timer, and modify it to be controllable with Z-wave. The components I used were Oracle Garden Supply 240v Digital Timer ($20 on eBay) and Fortrezz MIMOLite Z-Wave relay ($60 on Amazon).

I got lucky and the timer turned out to have been built in a modular way, where the timer control logic and the heavy duty relay are not soldered together, but connected via a 5 pin header. With a bit of reverse-engineering, I figured out that the bottom 2 pins control the heavy-duty normally-open relay (when the pins are unconnected the relay is open).

From there it was a simple matter of wiring up these pins to the normally-closed terminals on the MIMOLite, and – voila – I had myself a smart heavy duty power switch.


@mag wow this is good news. I’m very interested in this can you let me know how it works and also did you write a device type to use with smartthings etc. Does the cover fit back on and useable?

@llcanada So far it seems to work very well!
I drilled a small hole in the side of the housing cover to let the control wires out.
MIMOLite has various device drivers floating around… I used this one by Barry Burke, although I did have to replace the “Relay Switch” capability with just “Switch” to get it to work.

@mag I have a dryer 220v that I need to monitor and I think this will do it. The switch you use is for the garden and I wonder will it work for a dryer?

If you need to monitor a dryer, get a $25 1st gen home energy monitor from Amazon.

Also. I don’t really see how a mimo lite + case + contactors pencils out to any reasonable advantage over a aeotec heavy duty switch which is ul certified etc etc.

@codytruscott I will try that and thanks.