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EG4 Solar first, then batteries, then GRID as BACKUP ONLY - How to wire sub-panel and transfer switch

energyhunter

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Off grid neighborhood house. I am currently wiring (2) EG4 6500 inverters for split phase 240v. Most components purchased from Signature Solar... They are helpful but tech cannot volunteer information regarding sub panel or transfer switch types or installation advice. I will have a licensed electrician look over my work before I flip the switch.

I have (21) 445 watt solar panels mounted on the roof and (6) EG4LL batteries, about 30kw. My goal is off grid but still having grid accessible for back up only when the batteries are drained from prolonged lack of sunshine/PV input. I finally understand most of the system wiring needed but am confused when researching the transfer switch and how the sub panel is wired. I am NOT feeding into the grid and must prevent that. I just need my system to power all my existing main panel loads (not just critical loads) as already wired;

I've seen a mechanical transfer switch plate in a main box (used with a gas generator) but am thinking the EG4 must have software controls that determine the order of load service. I bought an 8 space 125 amp subpanel with a 60 amp breaker and do not intend to use it for additional circuits. Do/can I use a 100 amp breaker in the main to the subpanel that has a 60 amp breaker? Is a safety/disconnect switch necessary between the subpanel and the main?
 
Not sure exactly what you are asking.
the eg4 6500 inverters can NOT feed TO the grid. no worrys there
you should not need a transfer switch, I do have one but its not required
do you have the grid avbl if you want it ?

My house is all off grid except for the water heater
I have a 200 amp panel on the outside of my house with grid power. I have a 125 amp sub panel in workshop 100 ft away. This is where the off grid system lives.
at the workshop sub panel is a 60 amp breaker feeding the inverters
from the workshop inverters provide 60 amps to a 125 amp panel inside the main house which powers all house loads

I can provide more details if you have questions
 
Sounds like you want a whole home setup. In that case you could use as you mention a transfer switch or interlock before your main panel. Some people use a mechanical interlock on the main panel power supply breakers. This allows you to power the main panel only from grid or from your inverters but not both at the same time. For this setup you do not need a critical sub panel. Yes you could just feed grid into your inverters as "AC in" and use the inverter to select grid or battery/PV to supply your Main panel (no other power going to Main!) You however than are limited to the max power the inverters can deliver.

The EG4's do not have any load shaving or selecting capacity.

Do not mix a whole home concept with a critical load concept.

Untitled Diagram.png
 
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Not sure exactly what you are asking.
the eg4 6500 inverters can NOT feed TO the grid. no worrys there
you should not need a transfer switch, I do have one but its not required
do you have the grid avbl if you want it ?

My house is all off grid except for the water heater
I have a 200 amp panel on the outside of my house with grid power. I have a 125 amp sub panel in workshop 100 ft away. This is where the off grid system lives.
at the workshop sub panel is a 60 amp breaker feeding the inverters
from the workshop inverters provide 60 amps to a 125 amp panel inside the main house which powers all house loads

I can provide more details if you have questions
Thank you Texican for replying to my post. The idea of no transfer switch necessary is awesome! Yes, my garage has the main breaker panel, installed in 1987. All the house loads are there. Not sure of the amps for that but it is powering a typical 3/2 house 1600 sq ft. Right now I am 100% on grid. The inverters are right there next to the main and the sub panel will be also, on the other side.

Today I finished wiring the inverters, Nader breakers, bus/battery connections etc. Still have to connect the batteries together. The next part is the inverters hookup to the sub panel, then the sub panel to the main. I referred to Will Prowse's layout and also Eric's videos at "Country Living Experience". Eric has nearly exactly my system except my solar panels are roof mounted. Neither Will nor Eric show how their sub panel is wired to the main; really important considering I want to power that whole main breaker panel for whole house coverage, sunshine permitting. Do I just run the sub panel wiring to another breaker (amps?) mounted with the other breakers in the main? How does the main physically bypass it's grid input to accept battery/solar input in it's place?

I didn't mention that we are also building the same system for my son who lives around the corner with his family. We want both systems wired and ready for the visiting electrician next month. I very much value your input, thank you!
 
Sounds like you want a whole home setup. In that case you could use as you mention a transfer switch or interlock before your main panel. Some people use a mechanical interlock on the main panel power supply breakers. This allows you to power the main panel only from grid or from your inverters but not both at the same time. For this setup you do not need a critical sub panel. Yes you could just feed grid into your inverters as "AC in" and use the inverter to select grid or battery/PV to supply your Main panel (no other power going to Main!) You however than are limited to the max power the inverters can deliver.

The EG4's do not have any load shaving or selecting capacity.

Do not mix a whole home concept with a critical load concept.

View attachment 117793
Thank you MattB4 for replying to my post. If you read my reply to Texican then you might understand the nature of my confusion. I think I will post a photo of my system and main panel, possibly tomorrow with better natural light. I still don't understand the mechanics of how the main's input from the grid is cut off while the solar/battery input is powering the panel. I was thinking maybe the transfer switch is mounted by the utility between the outside meter and the main. I also have seen the sliding metal plate for the manual switching when using a gas generator for the whole house power. Thank you for the flow diagrams.
 
you can not send the inverter A/C ouput to the same panel where the inverter A?C input comes from., if that is what you are thinking.

you need to install that new panel and move all the house circuits that you want to be off grid to this new panel and thats where your inverter A/C ouput will go. this would be an off grid panel with no grid power at all.

the inverter A/C input will come from the main panel using grid power

is this what you are planning ?,

If its any easier

you could add a new main panel instead of a smaller panel
and move the grid main wires from the old main box to the new main box,
then keep all the house circuits in the old main box using it as the off grid panel ( may need the elec co to remove power while main wires are moved)

again, I know of no way you can use the same panel for inverter AC input and inverter AC output, at least not if you want to fully use the inverters utility supplement/passthru capabilities

if you just want the choice of powering the whole house with either grid power or solar/battery power then you could use the CB transfer switch/lockout method and do not even hook up the inverters AC input at all, of course if your batteries get low you will lose all power to house instead of automatic grid power coming on thru the inverters

are you familiar with the SBU and SUB functions that the inverters have ?
 
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Thank you MattB4 for replying to my post. If you read my reply to Texican then you might understand the nature of my confusion. I think I will post a photo of my system and main panel, possibly tomorrow with better natural light. I still don't understand the mechanics of how the main's input from the grid is cut off while the solar/battery input is powering the panel. I was thinking maybe the transfer switch is mounted by the utility between the outside meter and the main. I also have seen the sliding metal plate for the manual switching when using a gas generator for the whole house power. Thank you for the flow diagrams.
The main is cutoff either through a transfer switch that allows only one supply (utility or gen/inverter) to pass to your main breaker panel or through the breaker interlock method. However the interlock method has a problem. You may want the AIO to have AC in as well as battery/PV. Obviously you would not supply the AC Out of your inverter to a panel supplying the AC In to it.

If you go the sub panel route the EG4 would take power from the main panel from a breaker mounted in it going to the AC In at the EG4's and from the AC Outs you would feed your sub panel. At no point would you put power back to the Main panel or you would create a major fault since the utility and the EG4's are not in sync.

So you need to decide are you going to power the main or a sub panel? How you setup depends on that decision.

ETA: The utility company does not provide or wire in transfer switches. That is up to you to provide after the meter and disconnect (Note: not all residential electrical systems have a disconnect between meter and house Main panel.). For this you might need permits and a licensed electrician.
 
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Mattb4, exactly right
he spent 10 grand on the 6 batteries alone, with that investment, no way would I install it without AC in, allowing use of SBU and SUB modes. I use mine all the time if its partly cloudy. I run in SUB mode if my solar will not cover my load during parts of the day. I need to charge my batts during day not discharge them.
with 6 eg6 batts I have only 1 day, max of 2, maybe,, no extra days
having grid be able to supplement the solar in SUB mode is important, not to mention SBU mode automaticly going to grid power if BAtts reach X percent
 
The main is cutoff either through a transfer switch that allows only one supply (utility or gen/inverter) to pass to your main breaker panel or through the breaker interlock method. However the interlock method has a problem. You may want the AIO to have AC in as well as battery/PV. Obviously you would not supply the AC Out of your inverter to a panel supplying the AC In to it.

If you go the sub panel route the EG4 would take power from the main panel from a breaker mounted in it going to the AC In at the EG4's and from the AC Outs you would feed your sub panel. At no point would you put power back to the Main panel or you would create a major fault since the utility and the EG4's are not in sync.

So you need to decide are you going to power the main or a sub panel? How you setup depends on that decision.

ETA: The utility company does not provide or wire in transfer switches. That is up to you to provide after the meter and disconnect (Note: not all residential electrical systems have a disconnect between meter and house Main panel.). For this you might need permits and a licensed electrician.
Now I understand why I would not want to use the interlock method, thank you. About making a decision, my goal is to have whole house coverage, NOT 'critical loads only' coverage. So it seems to me I will need an electrician to install a transfer switch besides just looking over my system.
 
Mattb4, exactly right
he spent 10 grand on the 6 batteries alone, with that investment, no way would I install it without AC in, allowing use of SBU and SUB modes. I use mine all the time if its partly cloudy. I run in SUB mode if my solar will not cover my load during parts of the day. I need to charge my batts during day not discharge them.
with 6 eg6 batts I have only 1 day, max of 2, maybe,, no extra days
having grid be able to supplement the solar in SUB mode is important, not to mention SBU mode automaticly going to grid power if BAtts reach X percent
Yes, I think I would use the SBU priority mode at program setting 01 (in the EG4 manual) to configure load power source priority. (Sun, batteries, grid) At this point I'm assuming in SBU mode with no sun and depleted battery (I could set it at 5%) the EG4 settings program would access/affect the transfer switch to switch to grid power.
 
Now I understand why I would not want to use the interlock method, thank you. About making a decision, my goal is to have whole house coverage, NOT 'critical loads only' coverage. So it seems to me I will need an electrician to install a transfer switch besides just looking over my system.
its not a transfer switch that is the issue,
you need to get AC input for inverters from a panel connected to grid full time

you need a separate panel for all the breakers that are off grid ( the whole house) that is not connected at all ever to the grid. This where the inverters AC output will go.solar wiring.jpg

here is a scribbled drawing of my system, note that the AC input for the inverters comes from a panel connected to the grid, and the AC output from the inverters goes to a separate panel that has all the house circuits and is not connected at all to the grid
 
regarding my drawing above
I actually moved all the house circuits that were originally in the 200 amp main grid panel to a new 125amp off grid panel because I wanted it in the house not on the outside of the house next to the 200amp grid panel.

it would probably be easier for you to leave all the house circuits in what is now your main elec panel, and add a new main/grid panel next to it and just move the main grid power wires to the new panel rather than move all your house circuits to a new off grid panel
either way works
 
It is sinking in, Texican, finally; thank you for your patience. I'm thinking I should go with your option that uses a new main panel with nothing in it except a 60 amp double pole breaker that will power the old main that is acting as a sub panel with all the existing wiring and breakers.

I'm assuming the new nearly empty main will also have the big 200 amp breaker that is receiving the grid power....not sure if my 125 amp sub panel can work as that new main. If not I can buy the panel I need for that (?) and mount it but will need the electrician to connect the grid power in to the new main panel. I can have the wiring in conduit and ready for the electrician to connect. Am I getting warm?
 

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Sounds like you are figuring it out. Just for the heck of it I made a Critical load Sub panel setup diagram using a transfer switch.
Critical Load panel.png
 
yes you are getting closer

first, lets stop calling any of the panels a sub panel, unless its directly connected to a larger panel fed by the grid. I think that tends to be confusing.

second, if you dont want to move the house circuits to a new off grid panel then you will need a new 200amp panel to receive the grid main wires, you said that this new panel would only have a double pole 60amp breaker feeding the old main panel....no it wont...it will have a 60amp breaker feeding the inverters AC input, it can also feed into a transfer switch like matts drawing

matts drawing is perfectly fine, where his drawing shows :sub panel" that will be your CURRENT 200amp main panel
where his drawing shows "Main_ panel..that will be your new 200amp main panel that you have not bought yet

next lets talk about your electric dryer, range and water heater....
I have a propane dryer and range, but an electric water heater. There is really no way to run them on this solar system I left my water heater in the 200amp main grid panel
the water heater alone uses 4900 watts and can run 30 plus minutes,

you really should move the range, dryer, and water heater to your new main 200amp panel
I have a 12kw system with the same 6 eg4 Batts

also I see you have a heat pump, dont know how much juice that sucks... I have two 2 ton mini splits for heat/AC but mostly I run 1 at a time. they can each use up to 2500 watts max. Im in texas, summer is a bit..ch

what part of the country are you in?

You cant run a 200amp all electric house off a 9.3kw solar system and 6 Batts thru a 60 amp breaker
I think your system would need to be at least twice as large

you really need to leave some of those big loads on the grid
 
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Sounds like you are figuring it out. Just for the heck of it I made a Critical load Sub panel setup diagram using a transfer switch.
View attachment 118126
Thank you Mattb4. My brain has been on fire and you have helped to cool it down. Now I know how to approach the subject with an electrician. I will get back to you after I make some more progress. To be continued.....!
 
Sounds like you are figuring it out. Just for the heck of it I made a Critical load Sub panel setup diagram using a transfer switch.
View attachment 118126
Thank you Mattb4. My brain has been on fire and you have helped to cool it down. Now I know how to approach the subject with an electrician. I will get back to you after I make some more progress. To be continued.....! (Sorry, accidentally replied this on an earlier post)
 
yes you are getting closer

first, lets stop calling any of the panels a sub panel, unless its directly connected to a larger panel fed by the grid. I think that tends to be confusing.

second, if you dont want to move the house circuits to a new off grid panel then you will need a new 200amp panel to receive the grid main wires, you said that this new panel would only have a double pole 60amp breaker feeding the old main panel....no it wont...it will have a 60amp breaker feeding the inverters AC input, it can also feed into a transfer switch like matts drawing

matts drawing is perfectly fine, where his drawing shows :sub panel" that will be your CURRENT 200amp main panel
where his drawing shows "Main_ panel..that will be your new 200amp main panel that you have not bought yet

next lets talk about your electric dryer, range and water heater....
I have a propane dryer and range, but an electric water heater. There is really no way to run them on this solar system I left my water heater in the 200amp main grid panel
the water heater alone uses 4900 watts and can run 30 plus minutes,

you really should move the range, dryer, and water heater to your new main 200amp panel
I have a 12kw system with the same 6 eg4 Batts

also I see you have a heat pump, dont know how much juice that sucks... I have two 2 ton mini splits for heat/AC but mostly I run 1 at a time. they can each use up to 2500 watts max. Im in texas, summer is a bit..ch

what part of the country are you in?

You cant run a 200amp all electric house off a 9.3kw solar system and 6 Batts thru a 60 amp breaker
I think your system would need to be at least twice as large

you really need to leave some of those big loads on the grid
Thank you Texican. This really helped me understand and narrow my options. I'm sure you're right about me underestimating my power needs. I'll be adding more solar panels eventually to start. For now I need to learn with the system I have.

My heat pump is a 3 ton with a/c also that is a huge Trane central unit just purchased last year. I will install a soft start. I bought a 1200 BTU 30 seer mini split from Signature Solar to use in my garage. I'm in eastern Tennessee. My garage gets stupid hot/humid in summer and way too cold in the winter. This unit will cut down the extremes with very little energy so I can hang out in my garage and so can the batteries.

You've been a big help and, like I told Mattb4, I will make some progress and then touch base with you again in the future for your amusement.
 
its not a transfer switch that is the issue,
you need to get AC input for inverters from a panel connected to grid full time

you need a separate panel for all the breakers that are off grid ( the whole house) that is not connected at all ever to the grid. This where the inverters AC output will go.View attachment 118063

here is a scribbled drawing of my system, note that the AC input for the inverters comes from a panel connected to the grid, and the AC output from the inverters goes to a separate panel that has all the house circuits and is not connected at all to the grid
Quick question, if I understand your system correctly, if/when you have issues with the inverters and needed to take them "offline" for repair/replacement then you'd lose all power supply to your home? Thanks.
 
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