Noob EG4 18kpv design on 200 amp service

[Stryker777]

I'm getting ready to purchase our first inverter and large battery bank for our home. I'm looking at the 18kpv with 3 of the pro wall mount batteries. This will be feeding our home with an estimated daily usage of 34.6kw. I have a max 12kw of solar on my array, 30 400w bifacial panels. I'm not counting the bifacial benefit. Unfortunately, we have a very power hungry electric furnace that I won't be able to feed by inverter power and is not in my calculations. If power fails, our home can be maintained with 2 1500 watt space heaters. I've read that the 18kpv has grid passthrough. Does that mean I can configure it to use grid to supplement the inverter to feed the furnace when the grid is up? Or, do I need to tap the grid for the inverter, connect the grid terminals with a breaker disconnect and configure the 18kpv to feed back to the grid tap for my breaker panel? I can still add a transfer switch and connect the load leads for when the grid is down. I'm just having trouble finding what the grid passthrough is really capable of.
Thank you for any and all input! This will be my first home setup.

 

[DIYrich]

Grid to grid connection.
Main panel ti load connection. Can passthrough 200a.
Put furnace on smartload, and program to disconnect when grid down.

 

[Stryker777]

Does this look right?

 

[jeff.lankford]

That looks good to me. Comments:

1. You don't have to use 3/0 copper unless you have specific de-rating or local code reasons to do so. 2/0 copper is sufficient for the 200A service.
2. I assume you will have DC bus bars, not shown, between the batteries and inverter. Also, you haven't indicated the wire gauge you plan for the battery connections.
3. You haven't shown equipment ground on your diagram, so people will ask... N-G bond only at the main disconnect, and EGC continuity throughout the system to MTS, panel, inverter, battery cases, etc.

 

[Stryker777]

Thank you for the input! I won't need a bus bar at this time because I'm using all EG4 Power Pro wall mount batteries with paralleling cables. I'll reduce to 2/0. It saves money, so that's a plus. N-G bonding is at the disconnect on our pole. We are on rural utilities and they install breakers on the pole for us and bond in that panel. I'll add it to my diagram. I'll also update how the batteries are shown.
Thanks again!

 

[DIYrich]

I would move the furnace to the smartload so you don't overload the 18kpv when the grid goes down.

 

[Stryker777]

Thank you. Will do. Thankfully, it should be unnecessary soon so I can just disconnect it and rerun it after the main install is finished.

 

[gari51]

Does this look right?
View attachment 275183

Nice schematic. What software did you use to draw it with?

 

[Stryker777]

Nice schematic. What software did you use to draw it with?

Thank you. I used DrawIO at app.diagrams.net It is a free product. You can do a lot with it.

 

[kscessnadriver]

That looks good to me. Comments:

1. You don't have to use 3/0 copper unless you have specific de-rating or local code reasons to do so. 2/0 copper is sufficient for the 200A service.
2. I assume you will have DC bus bars, not shown, between the batteries and inverter. Also, you haven't indicated the wire gauge you plan for the battery connections.
3. You haven't shown equipment ground on your diagram, so people will ask... N-G bond only at the main disconnect, and EGC continuity throughout the system to MTS, panel, inverter, battery cases, etc.

View attachment 275184

You sure about 310.12 here? I thought it only applied to the service side, and once you’re no longer on the service side, it doesn’t apply

 

[Hedges]

If it is allowed and feasible to have inverter backfeed toward meter, either net metering or zero export with CT at meter,
I would move electric furnace to a different panel supplied directly by grid, not through inverter.

"estimated daily usage of 34.6kw"

kW is the unit for instantaneous draw; kWh for daily usage.
What are these two figures in your case?

If draw is low enough that inverter can handle it, then having furnace downstream of inverter on a load-shed relay (SoC based) is a good thing to do.

 

[jeff.lankford]

You sure about 310.12 here? I thought it only applied to the service side, and once you’re no longer on the service side, it doesn’t apply

No, but I've always interpreted the service entrance to mean the conductors all the way to the main service panel (main breaker panel), with or without a main breaker (i.e. "main lug" panel).

I haven't installed many services. I'm not licensed, but I've had three installations pass permit inspection without challenge using 2/0 run to the main panel, for a 200A service. If there's an NEC citation that shows this is wrong, I'd like to see it, and I'll stop telling people 2/0 is OK. I don't want to spread misinformation...

 

[zanydroid]

It specifically says service and feeder though. Anything that serves a full dwelling load.

I don’t see it ambiguous at all? And they even denormalized/repeated language to disambiguate it more

310.12 Single-Phase Dwelling Services and Feeders.

New Table 310.12.

www.electricallicenserenewal.com

(B) Feeders. For a feeder rated 100 amperes through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.

 

[Hedges]

I think one of the reasons that's OK is the NEC table is for 3 current carrying conductors (3 phase), but split phase only has 2 at full current, 3rd wire zero, for the highest power dissipation case.

Temperature rise through the wire's insulation is the same, but 2/3 as much from there through conduit to ambient.

 

[kscessnadriver]

It specifically says service and feeder though. Anything that serves a full dwelling load.

I don’t see it ambiguous at all? And they even denormalized/repeated language to disambiguate it more

310.12 Single-Phase Dwelling Services and Feeders.

New Table 310.12.

www.electricallicenserenewal.com

(B) Feeders. For a feeder rated 100 amperes through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.

Depends on which code cycle you’re on for sure. It was just more of a curiosity for me

 

[jeff.lankford]

Depends on which code cycle you’re on for sure. It was just more of a curiosity for me

Well, this same table is in my 1975 hard copy edition of the NEC, so how far back might you be thinking?

 

[jeff.lankford]

Well, this same table is in my 1975 hard copy edition of the NEC, so how far back might you be thinking?

(although it's not a table in 1975, it's textual, and it only goes up to conductor size 2/0 Cu for 200 amp)

 

[Stryker777]

After reading more into the code, I think 2/0 thwn is ok for the 200amp service, but I have a disconnect between. It looks like it says to the first disconnect then 3/0 after. Is that right? I already bought all of my 2/0 to do the job. It goes from pole on 4/0 aluminum to a 200a disconnect. Then I was going to use 2/0 copper thwn for 10ft from disconnect to my gridboss with a 200 amp disconnect. Then from it 24ft to my home panel with 2/0 thwn. I have a 200a breaker in the house but I won't be feeding that much from the inverter. My biggest concern is from the 10ft disconnect box to the grid controller. I can buy 3/0 for that, but didn't want to spend another $170. Still, I want to be safe though. Eventually, I think I'll change out to 3/0 to the house too, but I already got my 2/0 delivered.

 

[Stryker777]

New Diagram... Though I may need to change some things if 2/0 isn't going to work.

 

[jeff.lankford]

I still think you're good with 2/0 Cu all the way through the GB to your main panel. I have a 35ft run from my feeder tap to the inverter, and then back to the main panel via MTS, all using 2/0. I guess the code language considers it "service" to the first disconnect, and then "feeder" from that disconnect to the main panel disconnect. Note that 310.12 states both "service" and "feeder supplying entire load". It seems very unnecessary to me to step up in conductor size from the service wiring to the premise wiring.

Perhaps @timselectric could provide his opinion about what the code for 310.12 means.

 

[jeff.lankford]

New Diagram... Though I may need to change some things if 2/0 isn't going to work.

Your battery to inverter cable size of 2 awg looks too small. It should be sized for a sustained current of 312 DC amps. I would use a pair of 2/0 welding cables.

Your battery parallel interconnects need to be sized for 2/3 the maximum, or 208 A DC. A single 2/0 cable will suffice.

Flexboss sustained (6 minutes) peak power is 15 kW
(15 kW / 94% ) / 51.2VDC = 311.7 A

 

[wpns]

Your battery to inverter cable size of 2 awg looks too small. It should be sized for a sustained current of 312 DC amps. I would use a pair of 2/0 welding cables.

Your battery parallel interconnects need to be sized for 2/3 the maximum, or 208 A DC. A single 2/0 cable will suffice.

The EG4 paralleling cables (and the inverter cables that come with the batteries) are 2/0, so I suspect the above is a typo.
You'll want TWO of the battery <--> Inverter cables from the middle battery to the inverter, and then connect the two additional batteries to the middle battery. [Or I suppose you could connect each of the left and right batteries to the inverter and parallel them through the middle battery.]

 

[jeff.lankford]

The EG4 paralleling cables (and the inverter cables that come with the batteries) are 2/0, so I suspect the above is a typo.
You'll want TWO of the battery <--> Inverter cables from the middle battery to the inverter, and then connect the two additional batteries to the middle battery. [Or I suppose you could connect each of the left and right batteries to the inverter and parallel them through the middle battery.]

I would opt for your second configuration - a chain of batteries with positive to the inverter connected at one end and negative connected at the other end.

Connecting the inverter to the center battery with parallel branches left and right will cause the center battery to do more of the work - discharge deeper and recharge more. The batteries will stay equalized when idle, but the center unit would get more cycle life over time since it would have a lower path resistance to the inverter.

 

[Stryker777]

You are correct, it is a typo. I'm using the included cables and it is two positive and two negative that go up to the inverter. Depending on length of cables, I will try to hook positive to one end of the batteries and negative to the opposite end. I'm not sure they will reach though. They will have comm cables too, so I don't think it will be an issue. They haven't arrived yet, so I have a few unknowns. The 2awg was from the S2 site in the specs. I talked to them and they said it was a typo. I just forgot to update my layout.

 

[jeff.lankford]

You are correct, it is a typo. I'm using the included cables and it is two positive and two negative that go up to the inverter. Depending on length of cables, I will try to hook positive to one end of the batteries and negative to the opposite end. I'm not sure they will reach though. They will have comm cables too, so I don't think it will be an issue. They haven't arrived yet, so I have a few unknowns. The 2awg was from the S2 site in the specs. I talked to them and they said it was a typo. I just forgot to update my layout.

If the inverter cables aren't long enough to connect to either end of the chain, then doing what @wpns suggested by connecting the center unit in a 'T' configuration would be the next best configuration, rather than connecting both pos & neg to one end of the chain.