In electrical work, MC most commonly stands for Metal-Clad, referring to a type of electrical cable with insulated conductors wrapped in a protective metal armor. You’ll also see MC used as shorthand for other terms depending on context: MCB for Main Circuit Breaker on blueprints, magnetic contactor in motor control systems, or mC (lowercase) as the abbreviation for milliCoulomb, a unit of electric charge. The vast majority of the time, though, someone in the electrical trade saying “MC” is talking about Metal-Clad cable.
MC Cable: The Primary Meaning
MC cable is a factory-assembled wiring product made of one or more insulated conductors enclosed in an armor of interlocking metal tape, or a smooth or corrugated metal sheath. Think of it as pre-wired flexible metal conduit. The National Electrical Code covers it under Article 330, and it comes in a wide range of sizes, from 14 AWG (suitable for standard household circuits) up to 1000 kcmil (used in heavy commercial feeders). You can get it with copper or aluminum conductors.
The metal armor is typically aluminum, which makes MC cable lighter and less expensive than its close relative, AC (Armored Cable), which uses steel armor. Inside, the individually insulated conductors follow a standard color code: black for the first conductor, red for the second, blue for the third, then orange, yellow, and brown for conductors four through six. Cables with more than six conductors use striped combinations of these colors.
How MC Cable Differs From AC Cable
MC and AC cable look similar from the outside, but they handle grounding differently, and that distinction matters for safety and code compliance. AC cable relies on a thin metal bonding strip that runs along the inside of its steel armor. The armor itself serves as the grounding path. MC cable takes the opposite approach: it includes a dedicated equipment grounding conductor inside the sheath, but the aluminum armor alone is not rated as a grounding path.
There is an exception. Some MC cable products, often marketed as MC All Purpose (MCAP), include a bare aluminum bonding wire in direct contact with the sheath, making the armor and conductor combination suitable for grounding. These cables are specifically marked with language like “armor is grounding path component.” Healthcare-grade versions (labeled HCF) go a step further by adding an insulated green equipment grounding conductor inside the sheath, meeting the stricter requirements for patient care areas in hospitals and clinics.
A few other practical differences: MC cable can be supported at intervals up to 6 feet, while AC cable requires supports every 4½ feet. MC cable also doesn’t require the red anti-short bushing that AC cable needs at termination points, though manufacturers sometimes include them.
Where MC Cable Is Used
MC cable shows up in commercial buildings, industrial facilities, and increasingly in residential work. Its flexibility and pre-assembled design make it faster to install than pulling individual wires through conduit, while the metal armor provides far more physical protection than plastic-sheathed Romex. It’s a practical middle ground.
In healthcare settings, the HCF-grade version is standard in patient care areas. These facilities require a redundant grounding path to protect patients connected to medical equipment, so the cable needs both the armor-bonding combination and a separate insulated green grounding conductor. You can usually identify healthcare-grade MC cable by its green outer jacket.
When MC cable is installed horizontally through framing members like joists or studs, the framing counts as support, as long as the spacing between supports doesn’t exceed 6 feet. At junction boxes and equipment terminals, the code allows up to 3 feet of unsupported MC cable where flexibility is needed for connections.
Grounding and Safety Requirements
The grounding conductor inside MC cable works together with the cable armor and its connector fitting to create a low-impedance fault-return path. If a ground fault occurs (a hot wire touching the metal armor, for example), this path carries enough current to trip the circuit breaker or blow the fuse quickly, cutting power before the fault can cause a fire or shock.
The equipment grounding conductor inside interlocked-armor MC cable can be insulated or bare, and it can even be sectioned rather than continuous, as long as all sections are identical. If the cable includes any additional grounding conductors beyond the required one, those must have green insulation to distinguish them from circuit conductors.
Other Meanings of MC in Electrical Work
On electrical blueprints and construction documents, MC sometimes abbreviates Mechanical Contractor, identifying the trade responsible for HVAC and plumbing systems rather than an electrical component. MCB, a related abbreviation, stands for Main Circuit Breaker, the primary disconnect device in a panel or switchboard.
In motor control and industrial automation, MC can refer to a magnetic contactor. This is an electrically operated switch designed to handle high-voltage, high-current loads. Unlike a manual switch that you flip by hand, a magnetic contactor uses an electromagnetic coil to open and close its contacts remotely. They’re the standard way to start and stop large motors in factories and commercial buildings, and they include built-in protection against overload currents.
In physics and electrical engineering coursework, mC (with a lowercase m) is the symbol for milliCoulomb, a unit of electric charge equal to one-thousandth of a coulomb. One coulomb equals 1,000 milliCoulombs. This meaning is largely academic and rarely comes up in everyday electrical trade work, but it appears in electronics design and laboratory measurements.