The hole cannot be larger than one-third the depth of the joist, so the maximum hole size for a 2×12 joist (actual size 1-1/2 x 11-1/4 in.) is 3-3/4 in. diameterplenty big enough for running cable!

Cut rigid foam insulation into strips with a table saw or a circular saw. Cut the strips to fit between floor joists using a box cutter. How to Finish a Basement: Framing and Insulating Run a bead ...