What is the difference between MC cable and BX cable?

BX is an older trade name for armored cable that relies on the armor and a bonding strip for grounding. MC cable includes a separate insulated or bare grounding conductor inside the armor, which provides a more reliable ground path.

Can MC cable be used outdoors?

Standard MC cable is rated for indoor use and dry locations. Corrosion-resistant or PVC-jacketed MC cable is available for wet locations and some outdoor applications when listed for that use.

Is MC cable better than Romex?

MC cable offers more physical protection because of its metal armor, but it costs more and is harder to work with. NM cable is adequate and code-compliant in most residential wall and ceiling cavities where it is protected from damage.

What connectors are used with MC cable?

MC cable uses snap-in or screw-type connectors that clamp onto the armor and secure the cable to a box or panel knockout. Anti-short bushings are inserted at each end to protect the conductor insulation from the cut armor edge.

Do I need a permit to install MC cable?

Yes. Installing or replacing MC cable is permanent electrical work that requires an electrical permit and inspection in virtually all jurisdictions.

MC Cable (Metal-Clad Cable) — Armored Branch Wiring

An MC cable is a factory-assembled electrical cable with insulated conductors enclosed in a spirally wound metal armor sheath.

MC Cable diagram — labeled parts and installation context

What It Is

MC stands for metal-clad. The cable contains two or more insulated copper or aluminum conductors plus a green or bare equipment grounding conductor, all wrapped inside a continuous interlocking metal armor. The armor provides mechanical protection against physical damage from impact, abrasion, and rodent activity, and in some listed configurations it can also serve as an equipment grounding path.

MC cable is widely used in commercial construction and is allowed in many residential applications as an alternative to conduit or NM cable. It is more resistant to physical damage than Romex and can be run exposed in unfinished spaces where NM cable would need additional protection. The NEC covers MC cable under Article 330, which specifies permitted uses, support requirements of every 6 feet and within 12 inches of every box, and the approved fittings and termination methods.

The cable is manufactured by spirally wrapping aluminum or steel strips around the conductor bundle and interlocking the edges so the armor flexes without separating. An internal bonding strip or wire runs the length of the cable to supplement the armor's grounding continuity, and a PVC anti-short bushing is inserted at each termination to protect conductor insulation from the sharp cut edge of the armor.

Types

Standard MC cable has an aluminum interlocking armor and is the most common type seen in residential and light commercial work. Steel-armored MC cable offers stronger mechanical protection and provides magnetic shielding, making it suitable for sensitive circuits. MC-HL is a hospital-listed version with an additional insulated ground path required for patient care areas. Fire-alarm rated MC cable has special markings and conductor insulation for fire protection circuits.

Common residential sizes include 14/2, 14/3, 12/2, and 12/3 with copper conductors and THHN/THWN rated insulation. Larger sizes up to 500 kcmil are available for feeder and service applications. MC cable with a PVC outer jacket, sometimes called MC-PCS or corrosion-resistant MC, is rated for wet locations and certain outdoor applications where standard MC cable would corrode.

Where It Is Used

MC cable is used in exposed runs through basements, garages, crawl spaces, and attics, as well as inside walls and ceilings. It is the standard wiring method in multifamily buildings and commercial spaces where code requires metallic wiring methods for added physical protection. In residential work, some local codes that adopt more restrictive requirements than the base NEC mandate MC cable in lieu of NM cable.

MC cable is also commonly run in drop ceiling plenums, along steel stud framing in commercial tenant buildouts, and in renovation projects where exposed cable runs are necessary because opening walls is impractical. It does not require separate conduit, which saves labor on long horizontal and vertical runs.

How to Identify One

MC cable has a shiny or dull metallic spiral armor that looks like a flexible silver or gray tube. The interlocking armor pattern is visible as a helical seam wrapping around the cable. Cutting into it reveals individual color-coded insulated wires, typically black, white, and red with THHN markings, plus a green insulated grounding conductor. MC cable is stiffer and heavier than NM cable of the same gauge and makes a distinctive rattling sound when handled.

The cable jacket is printed with the manufacturer, conductor size, number of conductors, voltage rating, and listing marks. Anti-short red or blue bushings visible at box connectors are another identifying feature of a properly terminated MC cable installation.

Replacement

Replacement is needed when the armor is crushed, kinked, or corroded, when conductors inside are damaged or overheated, or when the cable is being rerouted for a remodel. Crushed armor can nick conductor insulation and create a ground fault or short circuit risk. An electrical permit is required because MC cable is part of the permanent wiring system, and the replacement cable must match the original conductor size and be terminated with listed MC connectors.