Main 400 Amp service to Distribution Panel (400 Amp) which connects to 4 Subpanels (225 Amps each)

Question

I am trying to fix the mistakes that a contractor made while installing and running the main connection as well as sub panels within our family home that was being rebuilt.

I need some input in regard to methods in which a 400 AMP single phase double pole connection can be distributed to the other panels within the house.

Currently, there is an aluminum over-head wire which connects from the pole to a separate meter box which houses the meter outside, it has a ground rod as well as copper ground wire connected to it. From there it is connected via a steel conduit using 3 large copper individual wires (of unknown AWG) next to it to a separate main breaker box housing a single 250 Amp Siemens QR22B250 double Pole Breaker. The Ground connection from the Meter box is bonded to the Neutral in this box.

There is a hole behind that second main shutoff box that runs 3 wires to a 40 Space Siemens S4040L1200 Panel Within the Garage. That Panel does not have a shutoff and has bonded Neutral and Ground Connections. It is the connection point for the remainder panels on the First, Second, as well as Basement Floors. This Siemens Garage Panel is not Plug on Neutral, The Other Homeline panels are.

The main feed wires coming from that Garage Panel to the Sub-panels are Aluminum SER with 3 Conductors being 1 AWG and one bare Ground being 3 AWG.

I am sure that connecting 3 panels to one panel that is rated for 200 Amps is not right, I limited the current to 100 amps per panel at that Garage Panel and disconnected the basement panel as it was not connected to anything being that it was not completed. All of the Subpanels are too small for the number of circuits going to them (30 spaces/circuits)

My questions are as follows, I have come to the understanding that I need to change that one Main Shutoff breaker box outside to a distribution box that can accept a 400 Amp Breaker from the meter and have 4x 225 Amp Breaker shutoffs going to the remaining panels which will be changed out for 60 Spaces/120 Circuits each. I need to know if such an outdoor rated main distribution panel exists and if this is the proper way to approach this. I am aware that the wire coming from the meter must be 600 Kcmil copper to support such a load.

Also, it has come to my attention that all the feed wires running to all the sub-panels is undersized for the load that they should be able to handle, SER 3C 1AWG/1C 3AWG from my understanding is rated for 100-110 Amps in a Dwelling Environment, I confirmed this from the manufacturer Priority Wire.

My correction would be to replace all of the SER wire to 300 kcmil-300 kcmil-300kcmil-4/0 AWG Wire, have each panel have its own Ground Rod at least 6 ft. apart outside, Neutrals and Grounds Separated, remove any and all bonding in the Garage Panel and only have the supposed distribution panel outside bonded to the neutral.

What would be the proper way to approach correcting this situation? My largest concern is the connection of all the sub-panels outside correctly and safely.

Edit: Additional Information: The Plan in and of itself doesn't specify any particular panels or breakers, it just states that x panel is of x number of circuits, and each circuit is x number of amps utilizing x type wire, and their locations.

Added Photos of the Outside Meter Box and Main Breaker Box as well as inside the Main Breaker Box.

Any Help would be much appreciated.

Thanks in Advance :)

Answer 1

Is the utility giving you honest 400A service? Because the 250A breaker there just makes no sense. What a difficult and expensive way to do that thing. Speaking of expensive, all breakers over 200A are not affordable, so that is not how 400A service is done. (and I wonder if your guys did not know that). 400A service is done as two 200A panels.

If it were me, I would plan to install two of these on the outside of the house. These are 200A Siemens "ranch panel / trailer panel" which have a main breaker, 8 breaker spaces, and "thru lugs" to take the full 200A onward to another panel. I would "plan to" install one immediately to the right of the meter pan right where the 250A is now. And another one just to the right of that. It's also common to put them on both sides of the meter pan, but I have a feeling wires will reach better if they are both on the right.

I would use RMC conduit with two LBs to drop out the bottom of the meter pan, then across the space allocated for the left panel, to the final location of the right panel. I would bend that mid-stretch so it pops up a bit, giving a way to get conduits into the bottom of the future left panel.

Now you have two 200A main breakers and 16 breaker spaces, along with two pairs of thru lugs.

I would populate the thru lugs and breaker spaces with runs to the various subpanels.

However, I would take care to try to have all the critical loads powered off one of the two 200A panels, preferably the right one. That will make life easier should you ever want a generator interlock or battery/V2X system.