18kpv - Check my wiring diagram with manual transfer switch

I'm installing an 18kpv with a rack of six EG4 batteries. My house power comes to a meter and that feeds straight into my Main Load Center with a 150A breaker. It is a Siemens load center, bus bar rated at 225A. I plan on using a 70A breaker in the bottom left side of the main panel going to the Grid input on the 18kpv. I will have a critical loads subpanel. In case of any issues I want to be able to feed the critical loads panel from either the inverter or switch it to grid (a second 70A breaker), disconnecting the inverter from the critical loads panel.

We use an average of 15KWH per day. My biggest loads are the wall oven (rarely used) and the well pump. I have been monitoring usage for several months with an Emporia system. Peak use is around 8,500 watts which only happens if the oven is on and the well pump kicks on at the same time. Propane for heat (hydronic radiant floor heat), hot water, cooktop, and dryer. I also have an EG4 24,000btu solar/hybrid minisplit. We live in New Hampshire so air conditioning usage is fairly minimal.

I would appreciate some feedback on whether my wiring diagram will work. The manual transfer switch would normally be in the down position feeding the Load output of the inverter to the critical loads subpanel.

Not having stared at this diagram for a considerable amount of time, I believe what you have will work just fine. I actually have something very similar except I'm off-grid so your grid output is actually my generator.

My switch isn't a super excellent switch so for me I would cut the power make the switch then enable the power since it's a mechanical throw switch.

Your neutral bond is in the main panel which is correct, the grounding looks correct. One item that looks odd is the CT on the main panel, this would in effect include current flowing even if the current was flowing to the critical loads panel and not the inverter. I would instead put the CT's between the inverter and the main panel if those CT's are for the inverter.

What is your hesitation about using the inverter as a passthrough and running everything on the inverter, not just critical loads?

You can have a bypass "just in case" the inverter goes kaput.

I've been running my entire property through a 15K with zero issues for 15 months now, before that for 2 years on two 6.5 K inverters, and before that two 5 K inverters. They handle clothes dryers, air conditioners, and EV charging without issue. I also use Emporia for circuit monitoring. I even have the Emporia EV charger and use it to do excess solar to charge the EV.

I would keep in mind that if you were wanting to sell back to the grid at any point, you would be limited to the 70A breaker.

jasonhc73 said:

What is your hesitation about using the inverter as a passthrough and running everything on the inverter, not just critical loads?

You can have a bypass "just in case" the inverter goes kaput.

I've been running my entire property through a 15K with zero issues for 15 months now, before that for 2 years on two 6.5 K inverters, and before that two 5 K inverters. They handle clothes dryers, air conditioners, and EV charging without issue. I also use Emporia for circuit monitoring. I even have the Emporia EV charger and use it to do excess solar to charge the EV.

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Hi Jason, no real hesitation. I was looking for a quick way to get up and running without having to deal with the power company coming out to pull the meter (no breaker at meter, straight into the main panel.) and getting an electrician to put in a 200A disconnect. It woud be ideal, just not ready for doing that yet. The critical loads panel ends up being just about all circuits in the house for me. I'll probably just keep the oven and some incidental circuits on the main panel. As I understand it - I can configure the 18kpv to use solar and battery to backfeed the main panel through the 70A breaker in the lower left of the main panel, zero export to the utility. If the grid goes down the inverter cuts anything from going to the main panel. The critical loads panel is supplied from the load output of the inverter unless I flip the manual transfer switch up to use power (limited to 70A from the breaker feeding it) from the utility. The inverter is isolated at that point. Why do this? Mostly because if something isn't working I want my wife to be able to just flip the transfer switch to just use the grid. I am hoping that everything is reliable enough to never really need to do this.

EG4_Jared said:

I would keep in mind that if you were wanting to sell back to the grid at any point, you would be limited to the 70A breaker.

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Thanks Jared. No plans to sell back. I'll be zero export which needs the CTs between my main and the meter. The 70A is plenty in my case. I ran the house on a 6500 watt generator during a few recent power outages (multiple days) off a 40A breaker. The 70A should allow me to run everything, based on about 8 months of monitored use. It helps to have the EG4 24,000btu minisplit with its own panels. Been running that since last Summer.

Next - I need to get some more panels. I only have six of the Canadian Solar 395W panels available for the 18kpv. I hope there is a sale/free shipping soon. Time to buy a full pallet!

MaikaiLifeDIY said:

One item that looks odd is the CT on the main panel, this would in effect include current flowing even if the current was flowing to the critical loads panel and not the inverter. I would instead put the CT's between the inverter and the main panel if those CT's are for the inverter.

Click to expand...

Hmmm...I have it there to prevent grid export. Pretty sure it needs to be between the meter and the main panel breaker. I'm fairly sure that the inverter will flow power into my main panel from the 70A breaker in the lower left of the main panel. The Grid connection at the inverter is bi-directional as long as there is utility power coming in.

Today I setup a temporary ground mount for six solar panels. I need to finish the cable runs to the inverter and with any luck I can power up the inverter tomorrow! My plan is to get my PV string into the inverter, have a couple of circuits transferred to my critical loads panel and then power up the system without making a connection on the Grid input on the inverter. I'll need to get the batteries charging, firmware updated, and get some settings dialed in, with Signature Solar's help!

Success! Six Canadian Solar 390W panels in series into PV1 of the inverter. Six EG4 rack mount batteries hooked up to inverter along with the EG4 communications hub. No loads or grid hooked up yet but firmware is updated on all (comm hub, batteries, inverter). Mobile app and web site logged into, all good. Batteries are charging now. Time to finish up the rest of the install! Oh, and yea I need to get more solar panels.