# Required junction box larger than joist

I have 2-2-2-4 AL SER cable running from my main panel in my unfinished basement to a sub panel in my attached garage. Since I have conduit for the last 5 to 6 feet to protect the conductors once they are on the garage wall side, information suggests I need a junction box mounted to one of the ceiling joists to splice the #2 THHN/THWN-2 wires to their corresponding conductor in the SER cable.

Using a 1-1/2 inch conduit and a straight horizontal run, tables show I need a 12 x 12 junction box. But this is larger than the width of the 2 x 10 floor joist. Is this correct?

And what is the correct method of splicing the 2-2-2-4 conductors to the the #2 THHN/THWN-2 conductors inside the junction box, do I use special connectors, or are there big wire nuts for wires this large?

• Are you sure you need a junction box, and can't send the SER on into the conduit? As I've read here, it is OK to have jacketed cable like NM & SER in conduit for protection purposes if the conduit is big enough. Nov 22, 2023 at 18:53
• Cable in conduit is code legal, it's just hard to pull. However, if only for 5-6 feet of straight run, it probably won't be a major issue. At that distance, you could buy really oversize conduit to make it an even easier pull and it won't be overly expensive. If you do decide to go the junction box route, and your box is deeper than the joist you're attaching it to, it'll just stick out through the ceiling. Call it a "feature"! Nov 22, 2023 at 18:56
• See exceptions to 312.5(C) and skip the box up.codes/viewer/minnesota/nfpa-70-2023/chapter/3/… (MN quotes NEC) Nov 22, 2023 at 18:58
• @isherwood For box sizing I was using the formula of 8X the largest conduit when it is a straight pull through the junction box. 1-1/2 conduit = 12 in box length. Does my situation not apply? Triplefault - That was my initial approach, however what screws things up is that once I am in the garage, I have an LB conduit body to make the right angle up to the subpanel, and learned the hard way that there's no way to bend the SER cable that tightly, plus the bend radius violations. crip659 - I would love not to do a splice if I don't have to. Nov 22, 2023 at 19:17
• Could I just run conduit and THHN/THWN-2 cables directly from the main panel, then under the ceiling joists to the LB body and up to the subpanel? It's about 30 feet, all interior, and then I won't have to worry about a "rat run" board for SER cable run perpendicular to the ceiling joists, or the splice box, or the LB body bend radius. And supplies are readily available. Nov 22, 2023 at 19:22