For a 12/4 MC cable with three insulated conductors (three hots and a neutral) and a grounding wire, applications are:

• Multi-way lighting circuits
• Two separate circuits with a shared neutral
• 240V applications with a neutral
• HVAC systems
• Control systems
• Emergency/backup lighting systems

MC cable, or metal-clad cable, is an electrical cable with one or more conductors enclosed in a metallic sheath. It's used for power distribution and control in various settings and protects against physical damage and electromagnetic interference.

Thanks to their metal armor, metal-clad (MC) cables can be exposed as per the National Electrical Code (NEC). The armor serves as an equipment grounding conductor.
MC cable can be exposed in dry, damp, or wet locations depending on the MC cable used. The cable's outer jacket contains information about suitable environments to expose the cable. While MC cable is durable, it should not be installed in areas subject to physical damage unless protected by conduit or other means.
MC cable must be adequately supported and secured according to NEC guidelines. MC cable must be supported at least every 6 feet for horizontal runs. Support can be used for MC cables, including straps, staples, ties, and standoff brackets.

Stripping MC (Metal-Clad) cable involves removing a portion of the metal sheath to expose the insulated wires without damaging them. Here's a step-by-step guide:

Tools Needed:

• MC cable cutter or a hacksaw
• Cable stripping tool designed for MC cable or a utility knife
• Pliers
• Wire strippers for the internal wires
• Safety glasses and gloves for protection

Steps to Strip MC Cable:

1. Measure and Mark: Determine the length of the cable sheath you need to remove. Mark this length on the cable sheath.
2. Cut the Sheath: If you're using an MC cable stripper, adjust it to the size of your cable, place it around the marked area, and rotate it around the cable to score the sheath. If you're using a utility knife, gently score around the circumference of the cable at the mark. Be careful not to cut too deeply to avoid damaging the internal wires.
3. Bend and Snap: Bend the cable back and forth at the scored line. This helps break the sheath at the score without damaging the wires inside. The sheath might not completely separate from an MC cable like some other cable types, but the bending will help loosen it.
4. Remove the Sheath: Use pliers to twist and pull the scored section of the sheath away from the cable. This exposes the internal insulated wires. For cables with a tightly fitting sheath, you may need to make a longitudinal cut to peel it back along the sheath. Again, be cautious not to nick the insulation of the inner wires.
5. Install Anti-Short Bushing: Slide an anti-short bushing (a red head) over the exposed wires and into the end of the remaining sheath. This protects the wire insulation from being cut by the sharp edges of the metal sheath.
6. Strip Individual Wires: Use wire strippers to strip the insulation from the end of each internal wire as needed for your connections, typically about 3/4 inch. Use the correct size slot on your wire strippers to avoid damaging the wire.

Yes, you can use Metal-Clad (MC) cable outside, but it has to be a subtype with a waterproof and UV-resistant jacket. If corrosion is a concern, the armor has to be corrosion-resistant.

MC cable can be plenum-rated if it is designed to be installed in plenum spaces in commercial or industrial buildings. A plenum-rated MC cable will have a "PL" or similar marking on the jacket. Examples of plenum-rated MC cables include healthcare facility MC cables, and LSZH MC cables. MC cables for residential use are not plenum-rated.

While MC cable's metal sheath already protects the wires, you can run MC cable in conduit in certain circumstances. Running MC cable through the conduit can offer additional protection in areas where the cable might be subject to physical damage. Running MC cable through the conduit can also be helpful in transitioning between different types of environments, such as from an indoor to an outdoor setting, where additional protection might be necessary.

In general, you can bundle up to 20 current carrying-conductors together. Note that the neutral wire is considered a current-carrying conductor and must be included in the count when bundling wires.
Also note that when cables are bundled together for more than 24 inches, the NEC requires that the ampacity of each conductor be derated according to tables provided in the NEC (typically found in NEC Table 310.15(B)(3)(a)). The derating factor depends on the number of current-carrying conductors in the bundle. If you want to avoid derating, bundle for at most 24 inches.
The physical size of the bundle should not be so large as to impede heat dissipation or make installation difficult.

Standard MC cable is usually not waterproof. MC Cable with a PVC Jacket (MC-HL or Type MC-PCS) can be used outdoors, and some MC cables are corrosion and UV-resistant and rated for direct burial.

Anti-short bushings, also known as "redheads," are small plastic inserts designed to protect the insulation of wires from the sharp edges of the metal armor in Metal-Clad (MC) cable. While the National Electrical Code (NEC) does not explicitly require anti-short bushings for MC cable, they are considered a best practice. Many manufacturers and electrical professionals strongly recommend them for safety reasons.

Yes, you can use Metal-Clad (MC) cable in residential applications, including construction.

Yes, MC cable can be surface-mounted in the basement, warehouses, and other locations where running cables in walls is not a suitable practice.
The National Electrical Code (NEC) specifies that MC cable must be regularly supported and secured within 12 inches of every cable termination. The exact spacing can vary depending on the installation specifics and local codes, but a common requirement is every 6 feet for horizontal runs. Cable straps, staples, or similar fittings suitable for MC cable should be used to secure the cable to the surface.