Rule of thumb for hole size in joist when running wires?

I'm going to be running wire in 2 x 10 joists (not engineered). The holes will need to accommodate 1-2 cables of 14/2 Romex. Can anyone suggest what size hole I should bore? Also, how far apart should adjacent holes be if I need more than one? Thanks!

 

We use a 7/8" auger bit for all our holes. You can run 3 or 4 cables through that with no problems. You can drill the holes pretty much anywhere you want on the joist as long as you stay 1 1/4" away from the faces. ( the sides you attach the floor or drywall to) You can also drill the holes right next to each other if you want but I normally stay a couple inches way or the bit just wonders over to the other hole

 

Sounds good, I was actually thinking 3/4" or 1", so 7/8" is a good compromise.

 

If the holes are drilled in the middle between the top and bottom face you will preserve more of the structural strength of the joist.

 

Also avoid the ends of the joists where they rest on the sill or beam. This is region of the joist which bears the greatest shear force so you want it to remain as structurally sound as possible. I recommend at least 1 foot in from either end and in the middle third top-to-bottom. A right-angle drill with a 7/8" auger bit does the job very quickly; borrow or rent one if you can. It's hard to get a straight hole using a regular drill because the drill plus the bit is greater than the 14.5" space you have between joists, so you have to start at an angle and try to straighten it out.