How many romex cables can be pulled through a 1" or 1 1/2" drilled hole in a floor joist before it's considered "bundling"? Common sense would seem to say that after 2 or 3 there would be the possibility of damage to the jacket.What code sections apply to this? Russell

310-15(b)(2)(a)99NEC considers stacked or bundled cables longer than 24" without maintaining spacing would need ampacity derating. As long as the hole is less than 24" long and the cables are spaced on either side of the hole they aren't considered bundled. I don't know how many will fit in the hole. That would depend on the size(s) of the cables.

I think that after 5 2-wire NM cables the inspector could say that the cables needed to be derated at 50%. After you go through 2 joists with a group of cables, then that's over 24" of the cables being effectively bundled together. I don't know how many inspectors are going to count to see if you have 5 or 6 cables, but I wouldn't go jamming too many in a run of holes either. A few rows of holes with a few cables each is better than one big set with 20 cables jammed into it.

Many inspectors do not consider the wires "bundled" between the joists unless wire ties or other items were used to actually create a bundle between the joists.
Don

Ck. your jurisdiction - San Fran only allows one NM cable per hole (yes, the studs/joists look like Swiss cheese).

Not to threadjack, but.. What do you think about the practice of ty-rapping wires in panelboards?? looks neat, makes heat.

Imho,it would be more of an issue in a commercial or industrial setting. More high amperage contunious loads.But then residential loadcenters tend to have less free space than a commercial panelboard.

Electure--That's a good point about the panels. I think the same rule applies. If it's over 24" of bundling, it's no good. Usually bundling in a panel is because of stranded wire and the difficulty in getting it to stay in place. A good idea is to use as few ty-raps as is necessary, pick a few key spots to get the wires into the right shape, and leave the ty-raps loose.