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 &quot;nipple&quot;) you can fill to 60%, so 1/2&quot; 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 &quot;larger of the small size holes&quot; to take 3/4&quot; conduit for 4AWG.