Proper way to extend circuits to subpanel

Question

I would like to move 8 x 20A circuits (room lights, ceiling fans, outlets in the bedrooms, and living room), and 1 x 50A (AC) circuit from left main panel to the right sub-panel. The sub is a "critical loads" panel, powered by my solar inverter (just off camera, against the left wall). The bottom-left 100A double breaker supplies supplemental grid power to the inverter. There is no back-feeding involved. I'd like to move these 9 circuits so that more of the house is covered by the inverter/battery/solar.

In the sub panel (125A), there are 8 empty slots on the neutral bus bar. Even though the ground bar is full, I understand those can be doubled up? My main question is, how do I properly extend the conductors from the main so they reach the sub?

My initial thought was to mount some junction boxes against the center stud, on the main panel side, just above it. Then pull the conductors out of the main, redirect into j-box, splice with wagos, then go out and up, over to the right through the stud, and down into sub.

I then read a comment on another post that the main panel is just a large junction box itself. There is already a grounded 2" EMT segment between the panels. Can I instead just wago-extend inside the main, through the EMT, and into the sub? Which is the better way / less hassle way to go?

Lastly, any room (bedroom, living room, dining room) outlet circuits I move need to be replaced with AFCI breakers, correct? (All kitchen-related, and bathroom-related outlets are already in the sub on GFCIs, or on AF/GFs)

This is in an unfinished garage, if that matters. Thank you for the help.

P.S. I know there are 3 SquareD breakers inside the Eaton sub, and that is a violation and needs to be fixed ASAP.

Answer 1

Using the existing big conduit is cheapest and easiest. A couple of 50 ft reels of wire (black and white) and a box of wagos and a couple of hours. It leaves the left panel a bit crowded with wires but if that doesn't bother you it's the way to go. If the existing wires to the inverter are short you might want to replace them, passing through the main panel rather than splicing them there.

If you don't like that, a big junction box above is a good idea for the 20A circuits or at least for the ones that are too short to reach the right panel directly. Install a ground bar in the jbox so you don't have a huge twisty rope of grounds or a chain of wagos. Run a flex conduit from it to the other panel, and splice loose wire rather than cables in the jbox and run them to the right panel.

Do you "have to" AFCI? If the inverter and sub installation are already inspected I don't think this work, if you do it yourself, triggers any permit or inspection requirements. Can't say for sure in your location. If the sub is new you probably do need AFCIs.

Answer 2

You can add accessory ground bars all day - that's not a problem. The panel labeling will list models for which the panel is pre-drilled. If your neutral+ground bar on the main panel is full, offload grounds to accessory ground bars. Grounds can be doubled or tripled to the extent the panel labelng says that is alright. Note the allowance on an accessory ground bar may be different e.g. less than the factory provided bars, commonly 3 on provided N+G bar but only 2 on accessory bars.

Neutral bars can never be doubled up (this is both a UL and NEC rule). End of conversation. Well not quite: UL requires the panel manufacturer provide enough neutral spaces for all the breakers that the panel is allowed to have. What commonly happens with subpanels is cheap people refuse to spend $6 on an accessory ground bar, and instead split double neutral bars to make one ground. Mysteriously, they suddenly have a neutral shortage. Gosh, how did that happen? ROFL

I can't quite see your bar on the right, but that right bar looks insulated from the frame (something a ground bar would never need)... and the top lug looks awfully big to be a ground on a 125A panel. I suspect the factory intended that to be a netural bar, and may have provided a crossover strap to link it to the other bar, with the intention that you buy accessory ground bars for subpanel use. I see other ground bar mounting sites well in reach of the ground wires.

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Your installer did the right thing by installing EMT between the two panels. It not only gives a wire passage, it also carries ground via its shell. Since it is under 2 feet long, you don't need to worry about thermal derate or conduit fill (well up to 60% but it'll be hard to exceed that).

As long as you're not in Canada, you can simply extend the wires using THHN individual wires into the other panel. You must extend neutral and land it in the same panel as the hot wires. You do not need to extend ground; ground can land in the box that the cable enters.

Note that THHN wire has a higher amp rate than Romex, so #8 copper THHN is good to 50A.

Answer 3

Cables/Extensions

A breaker panel box is a junction box. So you have 3 options, depending on how much excess cable you have and the direction each cable is coming from to get into the main panel. The same rules apply if there are circuits you want to move from the subpanel to the main panel.

• Move the cable.

Disconnect the cable from the existing breaker and neutral and ground bars. Pull it up and out of the main panel. Move it, removing staples, etc. if needed, so that it can reach into a knockout into the subpanel and connect to a breaker. If necessary, extend the cable with wires using Wagos or wire nuts to reach the breaker, neutral and ground bars. With the panels so close to each other, there is a very good chance this will work. When I had my heavy-up done, my electrician (I helped, which was fun) managed to get all but one existing circuit moved without much trouble.

• Connect through conduit

You have a nice big conduit connecting the panels with no wires in it. You can route existing cables from the main panel through the conduit to the subpanel. Because this is a short piece of conduit (< 24") you do not have to worry about multiple circuit derates, only conduit fill. Any cables that are not long enough can be extended with wires using Wagos or wire nuts. A quick calculation shows that the 50A circuit + 8 20A (12 AWG) circuits will fit in 2" EMT with plenty of room to spare.

• Replace the cable

Unlikely to be the case here, but you can always replace a cable if needed. In my heavy-up there was one cable that couldn't quite reach - probably about 1 foot short. My electrician initially put in a 4" box and splice in the box to a short piece of cable that ran into the panel. In the end I had him replace it with a longer cable, but that was a short run, probably around 10 or 12 feet.

AFCI

As far as AFCI requirements: That may very well be inspector-dependent. Arguably this is the same circuit, just with the breaker/endpoint moved a couple of feet. About the same distance as my entire panel moved with a heavy-up. On the other hand, an inspector could say that by moving it from the main panel to a subpanel it is now changed and not grandfathered. Unless you really want to add AFCI, it may be worth asking in advance, as those breakers are not cheap.

Neutral and Ground

You need to check the labeling for your subpanel. Typically two or even three grounds can be on a single ground bar screw. Neutrals usually can't double-up, but there should be sufficient neutral screws for all breakers. You should also put a nice wrap of white tape on the neutral feed wire.