Installing a subpanel with a service entry cable feed-through a Powerwall subpanel

Question

Based on this post on installing an EV charger, I decided to research installing a sub-panel next to an existing surface mounted indoor sub (Square D HOM2040L125PRB), which is used for Powerwall backup loads. The current sub-panel has all the loads connected through cables feeding into a 2.5" conduit nipple on the back of both the sub and main (Eaton BR) panels. I did a conduit fill calc and adding 3 new #2/0 wires and 1 #1 wire would bring it to 29%. For the angle pull the distance between the raceways in the current sub is about 20", the box depth of the main panel is 4".

Supplies:

• Square D HOM3060L225PC (Homeline, 1 phase, 30 spaces, 60 circuits, 225A convertible main lugs, PoN)
• 10' Southwire Aluminum SER cable 2/0-2/0-2/0-1
• 125 AMP Eaton BR breaker
• Bushings, clamps, fittings, etc.

My plan is to surface mount the panel next to the current sub and use a 2" nipple to connect them together. Strip the jacket off the SER cable and run each wire into the main panel through the Powerwall sub-panel. Terminate the wires and torque according to spec.

Was wondering if this was a solid plan and what "gotchas" or other complexities I can prepare for. The Powerwall sub has a jacketed ground wire from the main panel into the Gateway and then back to the sub-panel. From there another ground wire is terminated at my home's Ufer ground.

Questions/Concerns:

• The main panel is pretty crowded with all the splices from the Powerwall install. Getting to the ground bar basically requires pulling out all the wires so it can be accessed.
• If I'm using metal conduit would I still need to run a wire for ground? The ground wire in the SER cable is bare so I'm not certain if I can use that, just need to confirm it.
• Any experience with using a Tesla installed (or other solar battery provider) sub and having issues with using it as a feed-through? I'm not adding any load to the sub so I don't expect any issues, if anything I'll be removing some loads to the new sub-panel.

Any advice appreciated. Thanks!

Answer 1

Answering my own question with details on the installation such as changes I made and pictures with the different steps. Some changes from the original plan were to use 2/0 XHHW wire instead of SER and instead of going right of the battery backup panel I went left since it would give me more room for future circuit runs.

To get the sub mounted on a sturdy surface I put up some 3/4" RTD sheeting with a coat of primer on it. Once the board was up getting the panel mounted and level was quick.

For running the wires I shutdown the solar equipment and flipped the main breaker. In the main panel I put the 125A breaker higher up the panel so it wouldn't be next to the 90A solar breaker, this gave me more room to work with the 0/2 wire and I was also worried about part of the bus bar running extremely hot. It was difficult working with the spaghetti mess that was left by the solar installers. I basically had to pull it all out then bend and push-in the new wires and put all of the messy splices back.

There was no room for the neutral on the main ground bus so I tapped a lug onto the back of the panel above the current ground bar.

Then finally got the wires cut and terminated to the new panel.

For cutting the wires I bought a ratcheting cable cutter I found on Amazon, which worked really well. I used a torque wrench to secure the wires to breakers, lugs, etc. to the various specifications and also applied Noalox. I plan on opening up the panels soon to check the work and see if there are any glaring issues.

Additional Parts List:

• 30' 2/0 XHHW
• 10' 1 XHHW - Ground
• 2" rigid offset nipple + (lock-nuts, bushing)
• Eaton neutral lug (for main panel)
• Ratcheting cable cutter
• Noalox