The trouble with 'thinking' is that, when there is a rule, opinions are of little value. No matter how smart or logical you are.

Many are taught to NEVER drill a joist. Period. Yet, as Trumpy points out, we see the most extreme holes made by plumbers all the time, and the building never seems to fall down as a result.

The IRC (International Residential Code) pretty much agrees with Trumpy's assessment, though in a more specific manner. Let me illustrate, using an imaginary 2x10 with a 9ft. span.

Over that 9ft. span, NO drilling is allowed in the middle 3ft. (In many web discussions, folks confuse the "center of the span" with the "center of the width," which really confuses the issue).

In the end sections, no drilling is allowed within 2" of the edges. This means you have a 'permitted to drill' section (remember that a 2x10 is only 8-1/2" wide) that is 4-1/2" wide, in the central section, and 3ft. long.

Your largest allowed hole is 1/3 of that 8-1/2", or 3-5/32" diameter. There needs to be 2" of solid wood between the edges of every hole.

Let's assume that you goof, and make a pair of 3/4" holes with only 1" of wood between them. You would have to consider them as a single 2-1/2" (3/4 + 1 + 3/4) hole.

Just for comparison, let's look at the same situation if a TJI ("wood I-Beam") is used instead:

For a TJI, small holes like 3/4" are completely ignored, and can be placed anywhere in the web. Nor is there any requirement for spacing between such holes. You are NOT required to use the factory pre-punched sections.

A few final notes: I have found my cordless impact driver, when used with Irwin's "Superbor Max" bits, to make a much shorter assembly than the usual drill/chuck/bit arrangement. With a 'head length' of about 11", it easily fits between most studs and joists.

"Round" Romex can use a 5/8" hole. "Flat" Romex needs 3/4" minimum, and 7/8" is reasonable. Smaller holes are much easier to bore, and the drill will make many more between charges.

Likewise, I have found that it pays to be 'anal' in lining up your holes; it makes the wire pulls much, much easier.