According to code regulations, the holes need to be set back at least 1 1/4 inches from the front edge of the studs, or, you will need to use metal plates nailed to the fronts of the studs to protect the cables from accidental penetration from screws or nails.
When running cable along the length of studs or joists, keep the cable to the center of each, leaving a 1 1/4-in. minimum clearance on each side of the framing member. When running cable through studs, drill all holes at the same height so that the cable is run level to the floor. Drill holes 6 to 8 in.
We usually run them close to the height that the receptacles are to save wire many of the homes I have wired run from 8” to 24” with most 12-16” I like the taller ones because boring the holes through the studs is easier a little higher, just make you bore your hole in the center of the board so there is 1-1/4” or more ...
If the hole is not fire-stopped or draft stopped there is no limit as to how many cables you can run through it. If it is filled then derating begins when you install more than two cables. You could possibly install 4-14/3 or 4-12/3 cables in a fire or draft stopped hole with no effect on the final conductor ampacity.
IRC R602.
Any stud shall be permitted to be bored or drilled, provided that the diameter of the resulting hole is not more than 60 percent of the stud depth width, the edge of the hole is not more less than 5/8 inch (16 mm) to from the edge of the stud, and the hole is not located in the same section as a cut or notch.
The National Electrical Code (NEC) specifies that holes must be at least 1 1/4 inches from the edge of the stud. This requirement leaves about 1 inch of space in the center of a standard 2×4 stud. To avoid drilling too close to the edge: Use a 3/4-inch spade bit for 2×4 studs.
They are usually placed 16 inches apart on all walls. It can vary in older homes, but rarely would you find studs more than 24 inches apart. Windows and doors are also framed by studs for support. Above wide windows and doors, you might even find a wide header board.
Nonmetallic-sheathed cable shall be supported and secured by staples, cable ties, straps, hangers, or similar fittings designed and installed so as not to damage the cable, at intervals not exceeding 1.4 m (4 1⁄2 ft) and within 300 mm (12 in.)
12/2 is 1/2 inch wire. I would drill my holes 1 inch for easier pulling because the wire is stiff.
It is 9 without any derating. Actually, you can put as many wires in a conduit as you want. They just have to be derated according to Table 310.15(B)(3)(a) of the NEC. Deration begins with the 4th current-carrying conductor.
Still at 80% you're allowed 4-6 CCC's, so that would be 3, 12-2 Romex cables. Really, in a 3/4" hole, without stuffing it full, I doubt you could get many more than 3 anyway.
In a standard house, the electrical box height or outlet box height from the floor is typically set at 16 inches from the floor. This measurement is considered the standard electrical box height and complies with most electrical codes and safety standards.
You first need to trace the electrical wires in your wall with a magnetic or electrical stud finder (wires will be running through drilled holes in the wall's studs.) The standard height to run electrical wire in walls is typically 16 to 18 inches above the floor and in line with the wall's outlets, so start there.
In the codebook, section 334.30 states that flat cables must be stapled on the flat side of the cable, not on the edge. 2 This provides a tight wire connection to the stud and prevents any damage to the wire sheathing.
2. NEC Article 300.4 addresses protection against physical damage. Many folks who run nonmetallic-sheathed cabies (e.g., Romex) don't consider adding protection.
For general use receptacles, In commercial buildings it is limited to 180VA per duplex or single receptacle, therefore on a 12/2 Romex cable not otherwise subject to ampacity derating and protected by a 20 amp circuit breaker, that would allow a maximum of 13 receptacles.
A standard single-gang box has 18 cubic inches of space. That equates to enough room to hold 9 wires that are #14 gauge, 8 #12 gauge, or 7 #10 gauge.
Noting that Romex is the name of a popular brand of Non Metallic cable, of the type specified in the NEC (US National Electrical Code) as type NM. (Like “Kleenex” is a brand of facial tissue.) Romex is not permitted anywhere that it is exposed to risk of damage, to water (dampness), and/or to sunlight.
One of the requirements for permanent wiring, and thus for temporary wiring, was the need for adequate support. Article 336-18 stated that cable must be secured in place at intervals not exceeding 4.5 feet (1.37 m) and within 12 inches (305 mm) from every cabinet, box, or fitting.
By code, you must leave access to any splice anywhere. (The only exception is an irreversible crimp on a service entrance cable — a special case requiring an expensive crimping tool.) Splices in attics and crawlspaces are considered accessible as long as there is a hatchway into the space.
R602.
Studs shall be a minimum No. 3, standard or stud grade lumber. Exception: Bearing studs not supporting floors and non-bearing studs shall be permitted to be utility grade lumber, provided the studs are spaced in accordance with Table R602.
Most outlets and light switches will have a stud on the right or left side. The trim in your home, such as baseboards, crown molding, and other decorative finishing is usually nailed to a stud.
Utility grade studs shall not be spaced more than 16 inches (406 mm) on center, shall not support more than a roof and ceiling, and shall not exceed 8 feet (2438 mm) in height for exterior walls and load-bearing walls or 10 feet (3048 mm) for interior nonload-bearing walls. 2.