The Solution The National Electrical Code allows you to run four 12/2 nonmetallic sheathed wires through a single bored hole that has been fire- or draft-stopped with thermal insulation, caulk, or sealing foam, or if correct spacing is not maintained for more than 24 in. (610 mm), but only if they are not joined at the center.
There are several ways to connect multiple cables of different sizes and colors together. The most common method is to use a junction box. These can be bought pre-made or you can install one yourself. A professional electrician should do the job because it is dangerous work that requires special tools and knowledge.
Junction boxes are used to house electrical connections to external appliances or internal branch circuits. They provide a safe way to connect wires without exposing them to open air or other hazards. There are two types of junction boxes: metal and plastic. Metal ones are heavy and durable while plastic ones are lighter and easier to install/replace. Either type of junction box can be used to terminate and distribute cable signals. Standard metal boxes are 28 inches long and can hold up to 4 cables of equal size. Larger metal boxes are available if needed. Plastic junction boxes are usually about 1 inch shorter than metal ones to allow for insertion of conduit into which they will be mounted. Conduit is the term used for any of various materials, typically PVC or aluminum, into which wiring can be inserted and protected from environmental factors.
12. When nonmetallic-sheathed cables are "bundled" or "stacked" for more than 24 in. (600 mm) without preserving space, their ampacities must be lowered (adjusted, derated) in accordance with Table 310.15(B). (a). The heat created by the conductors cannot readily disperse when cables are grouped together. Therefore, care should be taken not to exceed the maximum bundle temperature as specified in Table 310.15(B)(a). Cables should be placed in conduit or armored cable to prevent excessive temperatures from developing in the interior of the housing.
Table 310.15(B)(a): Maximum allowable temperature for individual nonmetallic-sheathed cables. The maximum allowable temperature is 125° F (52° C) if the environmental condition is Class I (0% relative humidity [RH]) or if the electrical material is rated 150 V or greater; it is 115° F (46° C) if the environmental condition is Class II (20% RH) or if the electrical material is rated less than 150 V.
Cable impedance will change if you increase the number of wires within a conductor group. This is because resistance increases as the number of wires in a group increases. The effect on voltage would be similar to that of increasing the resistance.
When nonmetallic-sheathed cables are "bundled" or "stacked" for more than 24 in. Therefore, if the bundles are placed in close proximity, special care should be taken to provide adequate ventilation or insulation may be damaged.
Cables that are bundled or stacked for longer distances need not be further adjusted or derated because they are exposed only to mechanical forces.
In general, electrical distribution cable is designed to carry current within its specified limits for a certain length before failure will occur. Cables which have had many bends in their course or prolonged exposure to moisture will likely fail at some point after they become overloaded. An electrician should be consulted by a contractor to determine if your project requires metallic or nonmetallic wiring. If metallic, the appropriate size wire should be used to meet the needs of your project. If nonmetallic, then each segment of cable should be large enough to handle the current it is expected to carry.
You degrade if you have more than 9 current-carrying conductors. This image depicts a double. I use a staple (special staple) to go up to four cables, then 3M cable stackers to go up to five. You can secure or support Romex with anything; it does not have to be one of the mentioned options. But if you choose to use cable supports, make sure they are rated for Romex.
Here is how much cable you will need:
For current between 200 and 240 volts: 1⁄2 inch copper wire - 12 gauge (or 14 gauge for longer runs)
For current between 120 and 200 volts: 3/8 inch copper wire - 10 gauge (or 11 gauge for longer runs)
For current up to 120 volts: 1/2 inch copper wire - 2 gauge (or 3 gauge for longer runs)
All wires should be in one continuous length unless there is a reason to divide them up (for example, if they come from separate circuits). If you run out of one type of wire, you can always split another wire off of the same bundle.
It's best to buy cable in standard lengths, such as 100 feet, because this makes wiring jobs easier. However, if you have to cut up long lengths of cable, this article on how to splice electrical cables properly may help.