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

[Texican]

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.

No, I also have a transfer switch. I just didnt want to complicate the discussion on panels.

here is a pic of my system this is all in my workshop 100 ft from house

the AC in comes thru the left most conduit up from the floor. In the small junction box below the gutter and transfer switch I used morris split connectors to double each of the 4 wires. Then 1 set of AC input wires goes to the transfer switch and the other set goes to AC input on the inverters.
The AC output from the inverters goes to the transfer switch.

The transfer switch decides which power will go to the 125amp panel, located to the right of the transfer switch, which has the 60amp breaker going to the house panel

I did it like this so I could add some off grid outlets in the workshop at a later time

The middle conduit goin to the floor is the AC from the 60amp breaker going to the house

the conduit on the right is the incoming PV wires going to DC breakers before the inverters

 

[CoastieBalls1790]

No, I also have a transfer switch. I just didnt want to complicate the discussion on panels.

here is a pic of my system this is all in my workshop 100 ft from house

the AC in comes thru the left most conduit up from the floor. In the small junction box below the gutter and transfer switch I used morris split connectors to double each of the 4 wires. Then 1 set of AC input wires goes to the transfer switch and the other set goes to AC input on the inverters.
The AC output from the inverters goes to the transfer switch.

The transfer switch decides which power will go to the 125amp panel, located to the right of the transfer switch, which has the 60amp breaker going to the house panel

I did it like this so I could add some off grid outlets in the workshop at a later time

The middle conduit goin to the floor is the AC from the 60amp breaker going to the house

the conduit on the right is the incoming PV wires going to DC breakers before the inverters



View attachment 118204

Ok thanks. That all makes more sense then. I figured you would have a way to bypass in some way to account for repairs etc.

 

[bones1]

That's a good job right there.

 

[twyche]

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

I'm new and trying to learn. Why is there a separate transfer switch in the above diagram? Don't the solar aio units such as the EG4 have built-in transfer switches so that the sub panel could be directly connected to the AC output of the EG4 inverter?

 

[Mattb4]

I'm new and trying to learn. Why is there a separate transfer switch in the above diagram? Don't the solar aio units such as the EG4 have built-in transfer switches so that the sub panel could be directly connected to the AC output of the EG4 inverter?

It allows you to keep powering the sub panel even if the AIO is non functional or undergoing improvement. It is not required.

 

[DanielS]

It allows you to keep powering the sub panel even if the AIO is non functional or undergoing improvement. It is not required.

I’d recommend it 100%. No one wants to rewire the grid into their panel of a failure happens. I can bypass my entire system in 5 seconds if needed.

 

[twyche]

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

@Mattb4 In what situations does it make sense to use the whole home setup that you diagrammed above using the transfer switch vs when does it make sense to use the critical load setup that you diagrammed later, down below, in this discussion?

 

[Mattb4]

@Mattb4 In what situations does it make sense to use the whole home setup that you diagrammed above using the transfer switch vs when does it make sense to use the critical load setup that you diagrammed later, down below, in this discussion?

In most cases it has a lot to do with the capacity of AIO (and solar/battery) to carry loads. Typical homes in the US may have a 200a service. This is a 48,000w amount available. A 5000w AIO likely can not service all the loads but could handle several at a time of select loads. By splitting these loads away into there own panel they than can than be powered from an alternative power supply. However there are some higher capacity AIO that could possibly supply all the loads of a home. If this is the case you don't need a separate critical loads panel.

Pretty much invariably when running on alternative power versus grid power you need to do load management.

 

[DanielS]

@Mattb4 In what situations does it make sense to use the whole home setup that you diagrammed above using the transfer switch vs when does it make sense to use the critical load setup that you diagrammed later, down below, in this discussion?

I have mine set up with a transfer switch like that. I’ve had to use it twice now for different issues on the inverters. This allows you to isolate the inverters completely out of the house if you need to.

 

[twyche]

I have mine set up with a transfer switch like that. I’ve had to use it twice now for different issues on the inverters. This allows you to isolate the inverters completely out of the house if you need to.

Thanks. @Mattb4 created two different diagrams in this discussion. The first diagram was for a whole house setup. The later diagram was for a critical loads subpanel setup. I'm trying to understand in what situations one setup make more sense than the other.

 

[JCSchwarb]

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.

For our whole house system, I rerouted the main to a new input panel (first disconnect), left picture (meter on other side of wall). I added 3 double pole 60 breakers and two double pole 100 breakers. Each leg of the 60 amp feeds one inverter input. The 100 amp legs feed my new ouput panel that also has two double pole 100 amp breakers. The inverter outputs are connected to 60 amp breakers. When inverters are off, I turn off the 60 amp input breakers and turn on the 100 amp breakers. Note that the output panel (right side) then connects to my original main panel via 4/0 wiring on other side of the wall.

 

[Shimmy]

I'm trying to understand in what situations one setup make more sense than the other.

The whole house solution is cheaper initially, assuming everything works.

The critical load panel solution is significantly more flexible in working with unanticipated changes. Examples could be an EV charger or a hot tub being added, or switching major applicances from gas to electric; your PV system might not be big enough to support that, and with an off-grid inverter you don't have the flexibility to get support from the grid for overloads.

The critical load panel also likely improves resale value of your home. A 60A electrical service can be a bit limiting.

If you ever switch to a hybrid inverter down the road (grid tie with battery) then there are added benefits with the critical load panel as well.

 

[30362]

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.

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

@Mattb4 which transfer switch are you using? I just got finished connecting my system but I'd like to add a transfer switch like you have show above. Thanks!

 

[Stacking Functions]

For our whole house system, I rerouted the main to a new input panel (first disconnect), left picture (meter on other side of wall). I added 3 double pole 60 breakers and two double pole 100 breakers. Each leg of the 60 amp feeds one inverter input. The 100 amp legs feed my new ouput panel that also has two double pole 100 amp breakers. The inverter outputs are connected to 60 amp breakers. When inverters are off, I turn off the 60 amp input breakers and turn on the 100 amp breakers. Note that the output panel (right side) then connects to my original main panel via 4/0 wiring on other side of the wall.

I really like this setup. But I don't quite understand why you need the output box on the right? Couldn't you just use the 2 100amp circuits from the input box to power the old panel with all of the preexisting house circuits? I'm new to all of this so could be overlooking something obvious.
I know this thread is a year old but hopefully you see this somehow. Thanks!