Can we use an 'A-B Option Switch' between an EV charger and a heater on a 240 volt Line

Question

I recently helped my son-in-law install a ChargePoint Homeflex level II EV charger in his garage. It draws 48 amps max and we have it hardwired with #6 AWG THHN to a 60 amp breaker. He would like to install a 7500 watt Tempware forced air electric heater (https://a.co/d/0WoNGj9) in the same garage. It draws a maximum of 32 amps and recommends a 40 amp breaker and 8 AWG copper wire.
We would like to run it off of the same 60 amp breaker as the EV charger and avoid having to run a separate circuit from the other side of the house. I realize that the combined load would exceed the capacity of the 60 amp breaker and the #6 AWG copper but individually they would be within NEC requirements. He only uses the EV charger overnight when costs are the lowest and plans to use the heater during the day or early evening.
My question is:
Can we split off the existing line running to the EV charger with a 240 volt A-B option switch in the garage that would isolate the EV charger when the Tempware heater is running and vice versa when the EV charger needs to run?

There may be another option for a small sub panel in the garage feeding off the 60 amp circuit which was recommended in a similar question but I doubt that is workable within the NEC in this situation because the individual circuits need to be isolated.
We're open to any suggestions.

Answer 1

I started writing a long post about how/why this just won't work. But actually, I think it will work. It turns out you can get a double-pole double-throw safety switch that should do the job. Likely designed more for "two sources of power to one device", but it can be used just as effectively for "two devices on one source of power". For example, Eaton DT222URH:

But these things are quite expensive. A quick online search shows the $600 - $700 range. Very likely less expensive if you can get a local electrical supply house to sell it to you at a contractor rate (as opposed to a homeowner rate).

But a far cheaper solution is a subpanel. That gives you two options:

• Subpanel with 2 breakers and an interlock. That will work fine for now, using: breaker off/slide interlock/breaker on as the switching method.
• Subpanel with a larger feed. This is the better long-term solution as you can add additional circuits for other things. But in order to make this work you need a feed large enough for both loads at the same time, which means new cable or wires from the main panel. (And load calculations, etc.)

Assuming your garage has space for a subpanel (you need proper clearance in front of it, per code), I would put in at least a 12-space subpanel (you'll use 4 spaces right now). Wire up the existing feeder to the lugs and install breakers for the EVSE and heater. Install an interlock ("generator interlock" - you're using it for a different purpose here, and that's OK). Then in the future you can replace the feeder, remove the interlock and add other circuits as desired.

Answer 2

EV expert here. This is a terrible idea. Unless you're only running that heater a few hours a year, you will go broke running that heater. Better to spend your money on a Mini-Split heat pump, particularly the newer DIY friendly types, for 2 reasons: #1 massive electricity savings in winter. #2 A/C in summer. Because I bet you don't have A/C in there in the summer. Now you do.

Oh, did I mention that heat pumps take far less elecricity, which mean smaller breakers?

Now, let's add Part 2 to this. The trick is, what Technology Connections says right here.

Wow! Who knew 48A wasn't mandatory, and in fact is absolutely bonkers overkill for HOME charging. You're only replacing the day's use; just ABC Always Be Charging (during cheap electric rates) and you don't need much - 16A will cover almost everyone. The 48A setting exists because they same charging units are used at hotels, RV parks and AirBnB's where a traveler may need a complete overnight fill for onward travel.

The Chargepoint "FLEX" is defined by its ability to be set to 16A, 32A, 48A or 50A using internal switch settings.

So there are 3 ways we can go here.

First, go mini-split, derate the Chargepoint down to 32A or 40A if offered, and install a subpanel with both loads running concurrently. The rest of the wire capacity is there for the mini-split.

Second stay with the inefficient electric heater, set the Chargepoint to 32A, so now we have harmonized breaker size to be equal for both units. And a simple double-throw disconnect will suffice. I said double-throw not double-pole because DP is not needed.

Third, use a subpanel, and assure non-simultaneous use by applying an Interlock of these model numbers.

• Eaton CH uses CHML
• Square D "QO" uses QO2DTI
• Siemens panels use ECSBPK02

The trick - the really big trick - is finding a 4-space panel in one of those flavors that has all 4 spaces abreast (next to each other) so the interlock will fit. Most Siemens have an annoying gap, most Eatons are across from each other, etc. You can always go 6-space. Or more, and power more stuff in the garage, especially if you derate the Chargepoint to 32A.

All of this assumes you actually do have 60A of spare room in the Load Calculation. The vast majority of DIY installations never think about that, or for that matter, torque screwdrivers. We're going to see house fires - we already are, see Randall Cobb.