I appreciate your expertise in electrical systems, but you are not the only person reading this board, or this response. In answering any question on this board, I have to assume the person who asked the question knows nothing about the topic, and give as much information as I can, assuming that if the reader DOES happen to know something, they will take the extra information in good stride, and take what they need.
In your original posting, I had to assume, if you are doing wiring in your own home, and not aware of what's okay to drill through, that you are NOT a licensed electrician. By that line of reasoning, I felt it was responsible to MENTION the other items, in case you weren't thinking along those lines. There are WAY TOO MANY people out there who DO double tap their breakers, use the wrong size cabling, etc... I know, because I do home inspections, and the do-it-yourself wiring jobs I have seen in the past would make you shudder.
As far as the question you asked, the only part of a joist that is okay to penetrate is the center. You absolutely do not want to penetrate the top or bottom edges or within 2 inches of either edge. For confirmation on this issue, look at the TrussJoist system. It consists of two solid wood 2x2's joined with a sheet of waferboard. Penetrate the middle and you will be fine. Consider renting a 90degree auger drill to do it with, your holes will be straighter, and it is MUCH easier to use.