Zircon among others make an AC power detector, it’s like a stud

[Bruno1949]

sensor but sees AC power. It might be worth the money to buy one.

However, most drills are plastic bodied these days and if you actually drill into a wire it is unlikely you will receive a shock. Oh there will be a big arc and lots of light and the breaker or fuse will blow, but it’s unlikely you will end up dead. That said, it’s still better NOT to drill into live power lines. LOL.

Generally the wires are against the side of the stud at least an inch back from the wall so if you hit the stud square in the middle you should be fine.

Buy a good stud finder and maybe an AC detector and you will have a better idea of what you are drilling into.

I’ve been remodeling houses for 30 years. I haven’t hit a wire yet. Doesn’t mean it CAN’T happen, but it’s not common. Just make sure you aren’t barefoot in a puddle of water with a metal bodied drill and you will be fine. The worse that would happen is that you cut a wire and have to open the wall to fix it. Not fun but fixable.

Oh, “hard and set rules”? Not in home remodeling or construction. Sorry. I’ve owned a house where I had no use for a square or level because NOTHING in the house was square or level. People do some amazingly stupid things when they build or remodel a house. Rules are generally ‘modified’ to fit the situation.

Good luck on the shelf job. If you go into the center of the stud it will hold the shelves better anyway and avoid the wires.