Is conduit required when running a short distance to an adjacent 60 amp subpanel?

If you use cable, you are limited to the 60°C rating, so 6/3 isn't big enough for 60A - you'd have to go with 4/3

If you use conduit, and the terminations are rated for 75C, 6 (THHN) is fine. Also, if you use metal conduit, you don't need a grounding wire. The metal conduit is the grounding conductor.

Since it's less than 24 inches long, (a "nipple") you can fill to 60%, so 1/2" EMT, or IMC, or RMC will fit the 3x 6 AWG THHN wires you need (since you don't need a grounding wire, the conduit does that) - no large hole required. 75°C terminations are normal on service equipment, but do verify that yours are so marked - otherwise you are limited to 60°C ratings, in whch case you'll need the "larger of the small size holes" to take 3/4" conduit for 4AWG.

You can do it any way you want.

I would run several EMT short conduits.

What I would do, however, is run 3-4 short EMT conduits between the 2 panels. "Gee, that would require learning a new craft and buying $6 worth of fittings, why would I do that?"

• The EMT conduit takes care of all grounding. No ground wires at all needed.
• It makes it EASY to reroute circuits into the new panel.

It is perfectly legit to bring a circuit into the old panel, terminate its ground wire there, then extend only hot and neutral wires into the new panel. The several EMT conduits I mention make this easy.

I have installations with 2 panels next to each other like this, and having those conduit pipes really works nice.

1 near the bottom and 1 near the top for routing convenience. The third is for the feeder. Since the conduit is <24 inches, you can disregard thermal derates, so you only need to worry about conduit fill.

1" would be a much better choice if available (at least for the feeder). However a 3/4" pipe will support

• 3x #6 THHN, plus 6x #12 ...or...
• 3x #6 THHN plus 8x #14.

So you can bring #6 feeder + 3 circuits over in one pipe; 4 if they are all 15A. 1" would be a better choice as it'd let you run bigger feeder. I'm not sure what you are doing, but you may find 60A to be stifling.

And there's no earthly reason to be stifled. Spaces are CHEAP.

Think BIG on subpanels. Really. Really. Big.

We're talking breaker spaces... though bus capacity is connected.

I've been helping people for a long time here. The #1 mistake I see is people scrimping on the size of their subpanel, getting just enough spaces for today, and getting into a serious jam later because they've run out of spaces. Then they realize they could've avoided this by spending a measly $20 more on a bigger panel then. Suddenly scrimping doesn't seem so clever.

Or people think they must "match up" subpanel amps to feeder amps. That's not true at any level. Panel rating is a "redline" max rating like a tire rating. If you regularly drive 85 mph you want better than 85 mph tires. "Main breaker" size for a subpanel is also irrelevant.

Also, if you have any future aspiration for a generator, having a nice big subpanel is a great idea. Now you don't need a messy expensive transfer switch; you can simply get a panel interlock ($30-65) and switch the whole subpanel. Any circuit you want on generator, just migrate it to the subpanel. No limit to number of circuits - except for the size of the subpanel, of course.

Almost all panel knThree #6 Cu feeder wires can share the pipe with 6 #12 wireswill take can have as many wires as will fit. In practicality this means 1 conduit near top, 1 conduit near bottom, both for convenience of routing... and 1 conduit for the feeder.