I've been 100% solar since July but with the shorter days in winter and need for electric heat I'll probably need to go back on the grid. Although I probably won't be able to run the entire house I was hoping to run some circuits with solar. I would just plug them into the inverter(s), not going thru my breaker box. So I would want to run most of the house on grid power but some from my inverters simultaneously. The hard one is the water heater, it would be nice just to put a plug on the incoming power line and plug it in but this seems to be a no-no. It was recommended that I use a manual transfer switch, I'm looking at the Reliance CSR302, basically just a generator transfer switch. Then I could wire the WH thru the transfer switch. My question is is the transfer switch totally isolated from grid power, (my breaker box) when set to line? In essence I would be running most of my house from the grid but have the WH running from my inverters at the same time. I won't wire this myself I just need to know if this will work so that I can order what I need before the end of the year so that I can take the 30% tax break.

I put a reliance multi circuit transfer switch in my last house and the breaker had off/line/generator positions. When in the generator position it was isolated from the breaker box. It’s easy to wire in if you’re comfortable in the breaker box.

Because or the complexity of electric code and the fact that this isn’t as simple as a switch or outlet, I’d find a good electrician.

Shut your water heater breaker off in your panel when you transfer to solar. Can’t feed back then.

Working with utility electricity flesheatingvirus really has the right answer. Our house is off grid solar with a propane powered backup generator. When the propane powered generator dies the day before we were entertaining my entire family for Thanksgiving dinner (linner really), the electrician who installed the setup opened up the generator and spliced the wires going to the line input of the solar system to a pigtail plugged into my diesel powered welder. Ran the welder in the morning, charged up the batteries, then shut off the welder before guests arrived.

Cleaning up afterwards, I installed a transfer switch between the propane powered backup generator and the line input to the solar system. On the other side of the switch I wired an outdoor box where I could attach a cable that I could plug into my welder. Transfer switch in the up position, it feeds from the welder assuming it is connected. Transfer switch in the down position, it feeds from the (since fixed) auto starting propane powered backup generator. Handle in the middle, there is no feed on the line input into the solar system.

I felt comfortable making these mods as it was pretty straightforward and nothing was connected to the grid. Were I dealing with switch between power company line input and local generator input into my solar system I would have “called the man”.

I’ll change the 480v fuses on the wells as needed (after downing power, visually verifying that the knives are out, and then using a volt meter to verify no voltage at all between any of the three legs on either side of the fuses), but that is as close as I am getting to messing with line power.

ETA: If you’re 100% solar, do you have batteries? What system do you have controlling everything? Outback? Xantrax?

If your system is like ours (Outback), you may be able to take line voltage as an input into the system and configure you system to only use utility power when you want it to. Again, unless you are very familiar with the ins and outs of the system, I’d “Call the man” for help correctly configuring your system and safely (and legally) connecting utility power to your system.