Wiring diagram for 2 parallel inverters

[newtosa]

I'm planning the AC wiring for my inverters, at a country house where we have a backup generator and are planning a PV array and battery bank. Like many others, I'm using multiple 6000xp inverters (Luxpower, labeled as EG4) because of the AC grid pass-through functionality. I have a few questions for the group, and if you have relevant experience I'd appreciate your feedback.

Main objectives:

• The purpose of the PV/battery bank is to reduce reliance on the power company (not to eliminate it). No plans to sell back, given current power company capability/policies and net metering trends in general.
• For everyday use, the plan is to have the house load powered by PV power when it's producing, battery when PV is not producing, and a combination of PV+grid when load demand is high enough to require the AC pass-through.
• My family isn't as into this whole scene as I am, so there has to be an "easy button" for them to return to full power-company power if needed (e.g., all the inverters fail, or some similar situation). As a result, I planned a bypass circuit using a manual transfer switch... throwing that switch to grid, plus hitting the RSD on the inverters if needed, would bypass the inverters completely.
• The generator is there as a backup for short-duration outages at the power company (local weather, grid problems, etc.). My preference is to leave its wiring alone (i.e., it will continue to serve as a "backup grid" in this setup).
• All the other typical goals: no grid backfeed, etc.

Details and Questions for the group:

• The attached wiring diagram has the current hardware and wiring (shaded in white) and the planned additions/changes (shaded in yellow).
  • Currently (in white), the power company mains goes from the meter to the ATS. The ATS feeds either grid or genset power to the load side in a 200A main-breaker service panel. That main panel serves the large 240v appliances and a shop directly, and the house's 120v circuits in an interior service panel inside the house.
  • The new wiring (in yellow) will feed the ATS output to a distribution panel (200A bus rated), which feeds all the inverters through 50A circuit breakers (one per inverter). From the inverters, the 50A circuits are combined and fed to the MTS bypass switch.
  • The distribution panel's feed-through lugs pass power to the MTS bypass switch... normal operation for that MTS is to leave this grid circuit open and keep the inverter circuit closed (I know the diagram shows otherwise, but I got tired of messing with the drawing tool).
  • Does this wiring diagram accomplish the main goals?
  • Any concerns?
    • I still need to confirm my ATS has an outbound circuit breaker... otherwise of course I'll need the Distribution Panel to be a main-breaker panel, vs a main-lugs panel.
    • Also, the grid bypass circuit (at the top of the diagram) isn't switched on its own... I see pros and cons to that. The pro is that the MTS bypass switch is truly an "easy button" (no circuit breaker to check, in a scenario where the inverters all fail and there's no way for grid or genset power to get to the house). The con is that I would have to take the whole house down by opening the ATS outbound circuit breaker in order to work inside the bypass switch/MTS. Anything I should be considering here that I'm not?
  • Anything I'm doing that could safely be done with fewer steps or less-expensive hardware?
• The inverter's AC inputs are spec'ed at 8awg. I hear it will accommodate 6awg. Is that a wise move? In a 2-inverter scenario, I expect each inverter will be running between 3k and 6k watts during the summer peak hours (summer whole-house consumption runs 3kW-5kW in the afternoon, 4kW-10kW from 8pm-11pm, and 2kW-5kW until about 2am). If I see we're running the inverters too close to full duty rating, I'll add a 3rd inverter (which seems to be the appeal of the 6000xp).
• Generator AC connection: is there any advantage to routing this to the inverter's Generator Input vs as it's currently wired (into an ATS with the power company mains, where either source will appear to the inverter as Grid)?
• Neutral: Is this correct as drawn?
• Manual transfer switch rating:
  • Obviously there's a huge price delta between 100A and 200A MTSs.
  • I've had a Sense home energy monitor on the house for about 10 months now (covering the summer, when we often have both AC units and the oven running in addition to 1-2 circuits in the shop, etc.)... that peak load is 14.5kW, mostly to 240v loads (so 60 Amps). If you bump that up a little (some of the 14.5kW is to 120v loads)... even an adjusted 16kW is only 67A. I still need to put soft-starts on my non-inverter AC units, so that will come down some.
  • Nutshell: peak load in the summer is between 60A and 67A (and will be lower once I get around to soft-starting the compressors).
  • In a scenario where I choose a 100A MTS instead of a 200A MTS, here are the things I'm thinking about:
    • The 100A MTS doesn't accommodate 2/0awg copper (which is what I have now from the meter into the ATS, and on to the service entry panel).
    • If I were to use 2awg (rated for 130A if THHN) from the Distribution Panel to the Bypass Switch, and then to the SE/Loads Panel... the 200A breaker in my SE Panel may not adequately protect that wire. Would I need to change out the main-breaker in that panel to a 100A or 125A?
    • If I did all that... is there anything else I would need to solve for? Or should I keep this all as currently drawn, use the 2/0 wire, and just get over the cost of a 200A-rated MTS?

Thanks in advance for the feedback and ideas!
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Other background if helpful...

• I've reviewed the threads here:
  • https://diysolarforum.com/threads/dual-eg4-6000xp-wiring-please-review.78087/
  • https://diysolarforum.com/threads/6...for-system-with-optimizers-eg4-battery.77937/
  • and watched the typical youtube videos for multiple parallel 6000xps
• Not pictured (planning these separately and will pull it all together soon):
  • Generator wiring into the ATS (whole-house genset into the ATS has been in place for 2+ years; no plans to change any of that)
  • PV arrays and DC disconnects into the inverters (still thinking/sizing panels & strings into the MPPTs on each inverter)
  • Battery bank (60kWh gets me ~250 days of full-day coverage per year... am waiting for 280Ah vs 100Ah pricing to stabilize a little more, and will plan from there)
  • Stop/RSD circuit
  • etc.
• Based on my location and the AHJ, there are no inspections required. That said, it's important to me that the system is reliable and safe, and that we follow code with this project.

 

[ricardocello]

Quick Compliments: Nice drawing. You seem well organized, and listed your objectives.
Initial Thoughts: Your objectives are remarkably similar to what mine were, so I’ll give this a detailed look tonight.
Thanks for explaining what you want to do up front, it saves people asking lots of questions.

Quick Questions
Have you looked for distribution and combiner panels?
Have you considered using off-the-shelf generator interlocks on standard panels as an option for bypass switches?
What ATS do you have and will soon have another? Do you trust it?
Have you considered a 6x6 or 8x8 wiring trough under the 6000xp?

 

[newtosa]

Quick Compliments: Nice drawing. You seem well organized, and listed your objectives.
Initial Thoughts: Your objectives are remarkably similar to what mine were, so I’ll give this a detailed look tonight.
Thanks for explaining what you want to do up front, it saves people asking lots of questions.

Quick Questions
Have you looked for distribution and combiner panels?
Have you considered using off-the-shelf generator interlocks on standard panels as an option for bypass switches?
What ATS do you have and will soon have another? Do you trust it?
Have you considered a 6x6 or 8x8 wiring trough under the 6000xp?

Thanks for the quick feedback.
Here are a few things I've been looking at.

• Hardware:
  • Distribution options:
    • https://www.lowes.com/pd/Siemens-SN...in-Lug-Plug-on-Neutral-Load-Center/5014560029
    • https://www.lowes.com/pd/Eaton-BR-1...reaker-Plug-On-Neutral-Load-Center/1000551245
    • (if I need a main-breaker instead of a main-lug into the distribution panel)
  • Combiner options:
    • https://www.lowes.com/pd/GE-100-Amp-20-Spaces-20-Circuit-Main-Breaker-Load-Center/3151505
  • Outdoor vs Indoor: So far I'm thinking everything will be in an outdoor box, so I can mount it all to a cement-fiber board on top of existing drywall. Anything else I should be thinking of there?
  • While we're on this topic... it's not important to me that everything is the same brand... but similar dimensions might influence my choice. What would really influence my choice is the compatibility of actual circuit breakers. I wouldn't say I'm a prepper... but thinking through which circuit breakers might be available if, say, another global pandemic-induced supply chain disruption were to occur... that seems like only good sense. I haven't done any research on this at all (I've just worked within the boundaries of what's already in a house when I buy it)... have you spent any time identifying circuit breaker types that are more universally compatible vs others?
  • MTS options:
    • 100A: https://www.homedepot.com/p/GE-100-...ency-Power-Transfer-Switch-TC10323R/100171587
    • There's also a 200A version of this same switch... but it's almost a $500 difference based on where I am.
• Interlocks as an option to give me bypass switch functionality:
  • I used a manual interlock in the past (really just to treat my main SE panel as a Critical Loads Panel, when I was using a portable generator), and overall I was happy with it... but it did require *me* to actually be the one doing the switching. Since we spend a lot of time at this house - and when I travel for work my wife would be the one throwing the switch - I'm trying to keep it more straightforward for her.
  • I guess I really don't expect that to happen often, but as soon as I plan for the "best-case" scenario....
  • It's funny how many of us plan systems around that requirement: https://diysolarforum.com/threads/18kpv-check-my-wiring-diagram-with-manual-transfer-switch.84346/
• My current ATS is a Generac 200A (I think its CB is 225A rated, but can't remember for sure). It's been very dependable. I keep extra 6.3A fuses around, because in the early days the generator would lose track of whether the power-company mains was on or not... but I think this was probably more about me not understanding how the 12v battery-charge circuit on the Generac works (and not disconnecting the charge circuit before messing with the battery), than about the ATS reliability. I guess my design does depend on that ATS operating as intended at all times... need to think some more about that.
• On the wiring trough idea: exactly where I was headed next. On my boats I've gotten good at planning clean conduit runs for wiring, but it seems like there's too much going on with this project for it to look nice using individual conduit runs. Haven't thought through it yet... but I'm going to do some more thinking about keeping everything at about waist height using a trough. Haven't made battery decisions yet (am leaning server rack), so the height of my battery bank might also influence this.

Would love to continue to compare ideas, since it seems like we have similar projects/goals. Look forward to hearing more after you've had a chance to think through it.

 

[ricardocello]

For everyday use, the plan is to have the house load powered by PV power when it's producing, battery when PV is not producing, and a combination of PV+grid when load demand is high enough to require the AC pass-through.

I'm not as battery driven as you, I like to keep my batteries at 90% overnight in case of power outages during the night or in the morning.
But that is just a charge scheduling difference. I like every solar watt I generate feeding the loads, or charging the battery, in that order.

My family isn't as into this whole scene as I am, so there has to be an "easy button" for them to return to full power-company power if needed

I chose interlocks on two critical loads subpanels to go back to grid, and have shown the wife and family, and they get it (I think).
They should never need to switch it back, and have not for the last year.

Quite honestly, the switch to battery/PV when the grid goes down is so seamless, the only thing they notice is the oven clock going blank.

The generator is there as a backup for short-duration outages at the power company

I had already installed an outdoor L14-30 inlet to power critical loads, so I kept it when I added the critical load subpanels.
It is setup to feed into my Quattros, similarly how your xp6000 will work.

However, the EG4 Chargeverter changed my approach, so now I plug the Chargeverter into my generator L14-30 outlets to keep the batteries charged and supply power to the inverters. Way, way better than dealing with crappy generator power (no blinky lights), even with the double conversion losses. Not necessary if you have a nice generator with AVR, or a Honda inverter generator.

no grid backfeed

This is harder than you think when big inductive loads like HVAC shutoff. I have up to 1.25 seconds of backfeed, even with CTs and Energy Meters running at 10 Hz to compensate. I've posted here a bunch on this, but I don't know if the 6000xps are better or worse than my Victron Quattros. The laws of physics shall be obeyed, regardless, nothing is instantaneous. Maybe you have an ancient mechanical meter like I do, then you don't care because no one will notice.

The con is that I would have to take the whole house down by opening the ATS outbound circuit breaker in order to work inside the bypass switch/MTS.

I don't see a way around that. With my manual interlocks on critical load panels, when I switch back to grid mode to work on the system, I have to tell everyone in the house that the power will glitch for a second. All of the stupid Deebot vacuums leave their station and return. Very comical.

• Anything I'm doing that could safely be done with fewer steps or less-expensive hardware?

There are people on the forum who will undoubtedly help with this.

I hear it will accommodate 6awg.

I like oversizing, but not if they don't spec it. Get 90 deg C THHN 8 AWG, rated to 55A, keep it short, and run it to wire trough and use 6 AWG everywhere else, perhaps with a power distribution block to parallel the 6000xps. Make sure you have additional room for a third inverter.

Obviously there's a huge price delta between 100A and 200A MTSs.

Which is why I prefer panels with generator interlock kits, way cheaper, just as valid for code.

I still need to put soft-starts on my non-inverter AC units, so that will come down some.

Highly recommended, I use two EasyStart 368s for my two HVACs (3 and 3.5 ton).

the 200A breaker in my SE Panel may not adequately protect that wire. Would I need to change out the main-breaker in that panel to a 100A or 125A?

You MUST protect the wire with the appropriate breaker, no exceptions!

just get over the cost of a 200A-rated MTS?

I vomited, and went with panel interlocks. Turns out there are some cheaper ones that are still UL listed.

PV arrays and DC disconnects into the inverters

The 6000xp goes to 480 VDC, use as much of that as you can without going over it with Voc of panels at coldest temperature.
You've got 2 MPPTs, maybe orient the panels differently if you need to.
Roof or ground mount?

Battery bank (60kWh gets me ~250 days of full-day coverage per year.

Consider an outdoor or separate location for 60 kWh. I am reconsidering my battery location based on the "house burned down" thread.

Based on my location and the AHJ, there are no inspections required. That said, it's important to me that the system is reliable and safe, and that we follow code with this project.

I did my best to follow code for the same reasons, and the areas I was ignorant about aren't that critical.
Sometimes though, the code is less about safety, and more about industry protection and special interest groups.
Nevertheless, saying "I did everything to code" is definitely the right path.

 

[ricardocello]

Outdoor vs Indoor: So far I'm thinking everything will be in an outdoor box, so I can mount it all to a cement-fiber board on top of existing drywall. Anything else I should be thinking of there?

The 6000xps need to be indoor for temperature and ingress reasons.
You plan to use outdoor rated boxes inside on cement board? OK I guess, slightly more expensive.

wouldn't say I'm a prepper... but thinking through which circuit breakers might be available if, say, another global pandemic-induced supply chain disruption were to occur

My house is SquareD HOM (Schneider) and you can get them anywhere. QO would have been better, but oh well.
One of the sparky's here can tell you what is the most common (Eaton Cutler Hammer, GE, Siemens, etc.).
Also, if the SHTF, I expect you are going to have bigger problems than finding a breaker. I keep some spares for that reason.

My current ATS is a Generac 200A

Holy moly, those are expensive. But I understand the need.

 

[ricardocello]

Would love to continue to compare ideas, since it seems like we have similar projects/goals.

One of my objectives (not on your list) was that I did not want the house to be integrated with the inverters, charge controllers, and batteries.
So I rewired my house with Critical Load subpanels and 50A inlets.

All of my gear is on rollable movable racks. I could roll them right out of here if I wanted to (for inspectors or upgrades).
As the inlets are on the panel interlocks, everything is up to code on the wall in the utility room.
I'm not suggesting you do that, it's a lot of custom work.

This is your thread, but here is my single line diagram, maybe it gives you some ideas.
For me, planning all of this out was the fun part, I hope you are enjoying it.

 

[ricardocello]

Also, did you consider a single EG4 18kPV instead of two 6000xps?

 

[newtosa]

This is harder than you think when big inductive loads like HVAC shutoff. I have up to 1.25 seconds of backfeed, even with CTs and Energy Meters running at 10 Hz to compensate. I've posted here a bunch on this, but I don't know if the 6000xps are better or worse than my Victron Quattros. The laws of physics shall be obeyed, regardless, nothing is instantaneous. Maybe you have an ancient mechanical meter like I do, then you don't care because no one will notice.

For the way I'm planning to wire this, my understanding was that backfeed was prevented (meter --> ATS --> inverters --> loads panel, in the "normal operation" scenario; and meter --> ATS --> MTS (bypassing the inverters) --> loads panel, in the exception scenario). Do I have that right?

Make sure you have additional room for a third inverter.

All good advice; am going to plan space / wiring / service panel capacity for this possibility... that means I'll probably change the 100A combiner panel plan to 150A or 200A.

You MUST protect the wire with the appropriate breaker, no exceptions!

Agree for sure. So I would either:

1. Go with the 2awg wire from MTS --> SE loads panel and change out the mains-breaker on the SE Panel to a 100A (I'm limited first by the 100A-rated bus on the MTS, then by the 115A-rated 2awg 75C THHN)
2. Keep the 2/0awg wire as planned, and change to a 200A-rated MTS
3. Use an interlock device on a more reasonably-priced panel with 200A CB.

Is that about right? I don't like option 1, so I'll think further about options 2 and 3.

Turns out there are some cheaper ones that are still UL listed.

Will do a little more searching there; thanks for the tip. I still think that "just switch everything over to the power company" has to be as easy as throwing one switch when I'm out of town)... so if I can find a listed MTS for less, that might be the magic.

The 6000xp goes to 480 VDC, use as much of that as you can without going over it with Voc of panels at coldest temperature.
You've got 2 MPPTs, maybe orient the panels differently if you need to.
Roof or ground mount?

Haven't really gotten into planning the PV yet. Thanks for the advice on maximizing the VDC into the inverters (subject to cold Voc)... I like the thought of 2 orientations, and if I go rooftop that will work perfectly. We have enough space for ground array, so I need to think about the pros/cons of trenching and copper vs install and maintenance on the roof.

My house is SquareD HOM (Schneider) and you can get them anywhere. QO would have been better, but oh well.
One of the sparky's here can tell you what is the most common (Eaton Cutler Hammer, GE, Siemens, etc.).

I think I'll plan around the Eaton panels (seems they are approved for the widest range of different breaker brands). Do others agree there?

One of my objectives (not on your list) was that I did not want the house to be integrated with the inverters, charge controllers, and batteries.
So I rewired my house with Critical Load subpanels and 50A inlets

That's a pretty interesting idea! It may give me some ideas for mine too (more on the modularity/upgrade side, vs the inspection side for this particular house, but I definitely understand the use case).

Also, did you consider a single EG4 18kPV instead of two 6000xps?

I did. I like the idea of it... but keeping an on-hand spare is much more expensive that way. Other than avoiding the need for a combiner box (and an extra distribution CB), is there anything else I would gain with the 18kPV?


Really appreciate all the feedback and ideas!

 

[newtosa]

A question for the group: For the way I'm planning to wire this (meter --> ATS --> inverters --> loads panel, in the "normal operation" scenario; and meter --> ATS --> MTS (bypassing the inverters) --> loads panel, in the exception scenario, my understanding is that backfeed is prevented. Do I have that right?

 

[ricardocello]

A question for the group

This Planning subforum does not get a lot of traffic, and as much as cross-posting is frowned upon, I would post in the main DIY Solar Forum with a link to your original post, but you need an attention grabbing title like “Dual EG4 6000XP AC Wiring and Disconnects for the Country House”
That should get the 6000xp people and the sparkys interested. The forum has over 100,000 members, it can be challenging sometimes.
Or ask a moderator to move your thread as is. But I’d still change the title.

 

[newtosa]

This Planning subforum does not get a lot of traffic, and as much as cross-posting is frowned upon, I would post in the main DIY Solar Forum with a link to your original post, but you need an attention grabbing title like “Dual EG4 6000XP AC Wiring and Disconnects for the Country House”
That should get the 6000xp people and the sparkys interested. The forum has over 100,000 members, it can be challenging sometimes.
Or ask a moderator to move your thread as is. But I’d still change the title.

Thank you sir! Appreciate all the advice and thinking through this.