Multiple Panels on One Feeder
This isn’t specifically a green building question, but I know there are people here who likely have experience with these parts of the NEC.
(Diagram attached for reference)
My current electric service (that I installed ~3 years ago, before my project scope-crept and I decided to go all electric) has a 200A combination meter-disconnect on the outside of the garage, feeding a 3/0 copper-in-2″ EMT feeder. The feeder passes through a 100A main breaker panel in the garage, where I used Siemens ECRLK250 tap blocks to tap the feeder and supply the main breaker in the panel — this follows the NEC tap rules for the smaller tap conductors supplying the 100A main breaker. The main feeder conductors continue out the bottom of the garage panel and on to the main panel in the basement, a 200A rated, 40-space main lug panel. This has all been approved and AFAIK follows all relevant NEC rules.
Now, as my project has exploded, and water heating, cooking, and HVAC are all moving to electric, I realized the 40-space panel doesn’t have enough spaces, and I should have put the panel on the other side of the basement staircase to have easier access to the kitchen and laundry circuits. I’m planning to add a second panel on the other side of the basement and reroute the original feeder to it, while leaving the existing panel which primarily serves general lighting and receptacle loads (kitchen, laundry, and HVAC have not been wired yet). My first thought was to just feed the current panel as a subpanel off the new panel, but then I remembered the tap rules and thought I could actually just add a big junction box to the feeder conduit and split the feeder into two for the new and existing panels.
I’d just continue using 3/0 copper for both sides of the split, and both panels would be 200A rated, so this doesn’t actually fall under the tap rules (which define a tap as a smaller-than-normally-allowed conductor). I *think* this should all be fine, and I haven’t found anything in the NEC that limits the number of breakers or panels that can be served by a single feeder, but it’s also not something I’ve done before. Any objections to this plan from those who’ve read the NEC more thoroughly than I have?
(As an aside, the keen-eyed might notice that the existing condition actually slightly violates NEC — the 200-A main lug panel isn’t sufficiently rated given the 200A breaker on the feeder plus the 20A solar PV connected to the garage panel. The garage panel is fine because the PV breaker is at the bottom of the bus with the appropriate stickers saying not to move it, and the 3/0 feeder itself is adequate, and the inspector didn’t call me on it when I installed the solar panels….. Regardless, as a separate project, I’m looking into replacing my meter main with a Siemens MC0816B1200RTH, which would give me a 200A rated bus structure where I could replace the main with a 150A breaker, allowing expansion up to 50A PV without overloading anything, and providing additional breaker slots so I could tie said PV and maybe an EV charger and a feeder to another building into the exterior panel. Unfortunately, that panel doesn’t have bypass capability, and my utility requires bypass horns, so I’m asking them if they can waive that particular requirement.)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part