EV Shared Power – GreenBuildingAdvisor

You would use a manual transfer switch to do this, such as this:

https://www.zoro.com/siemens-nonfusible-safety-switch-heavy-duty-600v-ac-3pst-30-a-nema-1-dtnf361/i/G8652892/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping%20feed&utm_content=free%20google%20shopping%20clicks&campaignid=21427636968&productid=G8652892&v=&gad_source=1&gclid=CjwKCAiA3Na5BhAZEiwAzrfagHJbSVKZ6wV6zdrqqShGX30BjqUrHk8sMSu6rtF3sfNRgSzFvZrrgRoCFfQQAvD_BwE&gclsrc=aw.ds

Note that you’d just use two of the three contacts on the “3 phase” switch when using it in your application. You could possibly find a 2 pole switch too, I just posted a link to the first thing I found as an example of what I’m talking about.

It’s much cheaper to just use a small electric panel like this though:

https://www.amazon.com/Siemens-E0408ML1125SU-Circuit-125-Amp-Surface/dp/B00002NB09/ref=asc_df_B00002NB09?mcid=b8e72fcf434a35afb552b89f93a80942&tag=hyprod-20&linkCode=df0&hvadid=693410589815&hvpos=&hvnetw=g&hvrand=1506806078878310277&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9016990&hvtargid=pla-362690116767&psc=1

Put a pair of 20A double pole breakers in that panel, one for the A/C, and the other for the EV charger. Only turn on the breaker for the device you want to use.

Note that you could just have both devices connected at the same time if they are both plug-in (not hardwired) devices. The existing circuit’s 20A breaker will trip if both units try to run at the same time and overload the circuit. This is similar to having two hairdryers connected to one circuit: you can run either hair dryer without trouble, but if you turn them both on at the same time, the circuit will trip. It is safer to have some kind of interlock as you’re asking about though.

BTW, most EV chargers are going to want a 240v 40A circuit to be able to charge at full power (some need even more than this). You can usually set the charger to tell the car to only draw up to xx amps though, so I recommend you “dial it down” so that it knows it only has a 20A circuit available, which allows for 16A in “continuous” (more than 3 hours) loads, which would include the EV charger.

Bill