What Is MC Cable? | Pro Wiring Basics

New to metal-clad wiring? Here’s a plain-spoken guide that answers what MC cable is, where it fits, and how to install it cleanly without code headaches. You’ll get the short story first, then detailed guidance with diagrams, tables, and build tips.

What MC Cable Means

MC stands for “metal-clad.” It’s a factory-made cable with one or more insulated conductors inside a metal armor. The armor may be interlocked aluminum or steel, or a smooth or corrugated tube. Many builds include a bare or green equipment grounding conductor under the armor. Some versions carry a protective outer jacket for wet areas or sunlight exposure.

In the field, you’ll see compact whips for lighting and devices, long home runs above ceilings, and large feeder assemblies pulling through long corridors. Listings follow UL 1569, and use rules live in NEC Article 330.

Common MC Variants And Typical Use

Why Electricians Pick MC Cable

Speed and order. The assembly arrives with conductors sized, colored, and ready to cut. Pull the run, trim the armor, land the conductors, and move on. No bending of raceway for every turn, no separate pull wire, and fewer boxes in open spaces. The armor gives mechanical protection that regular nonmetallic sheath can’t match, and the ground path rides inside the cable.

On jobs with repeat layouts—think offices, apartments, and schools—prefab MC whips shave hours and reduce rework. Job leads stay tidy and crew pacing improves across floors too. For big feeders, large MC with interlocked armor pulls well and resists kinks that ruin conductors in tight spots.

Taking MC Cable From Spec To Install

Good results start at layout. Note the wiring method on the drawings, confirm the edition of the code in force, and match the listing to the space. Plan boxes and device depths so connectors sit square. Keep runs neat and high, keep hangers regular, and avoid sharp edges that scar armor.

Pick connectors made for the armor type and jacket. Tighten locknuts evenly, and use insulating bushings where the connector design calls for one. Many brands ship red anti-short bushings; for MC they’re not required by the code, yet some crews still use them as a belt-and-suspenders detail.

Code At A Glance

Three checkpoints come up on nearly every inspection of MC work:

• Securing and hanging. Place hangers no more than 6 ft apart, and secure within 12 in. of every box for small branch-circuit sizes. Larger vertical runs may have wider spacing with the right listing. See 330.30 for the exact rules.
• Bend limits. For interlocked or corrugated armor, keep the inner-edge bend radius at least seven times the cable’s outside diameter. Smooth-sheath builds use different multiples. See 330.24.
• Fittings and continuity. Use connectors and couplings marked for MC. The equipment grounding conductor runs inside the cable; do not rely on armor unless the product is specifically listed for that function.

For classroom-grade refreshers on these rules, see EC&M’s plain-English coverage of MC spacing rules and bend radius.

MC Cable Vs AC Cable

Type AC (armored cable) and Type MC look alike, yet they’re not the same. AC relies on the armor, plus a thin bonding strip, to serve as the equipment grounding path. MC carries a separate grounding conductor inside the armor. That single difference changes where each method can be used and which fittings qualify.

AC has dry-location limits and narrow scope in many cities. MC reaches more spaces, pairs well with wet-rated jackets and conductors, and scales into large feeders. When a spec calls out “armored cable” by habit, ask which type the engineer intends, then bid with the matching listing.

Where You Can Use Metal-Clad Cable

MC shows up across commercial interiors, mechanical rooms, and industrial floors. The method can run exposed, concealed, above ceilings, or on cable tray when the listing and the tray rules both allow it. In garages, rooftops, or other damp spots, use jacketed MC with conductors marked THWN-2 or XHHW-2. For rooftops, look for sunlight-resistant marking.

Hazardous areas require MC-HL with matched HL fittings. Some local codes set extra limits on cable wiring in high-rise corridors, plenums, or patient-care spaces. Check the adopted code cycle and any city amendments before release.

Planning Runs That Inspectors Like

Keep parallel routes and level lines. Use beam clamps and straps that seat the armor without pinching it. Avoid long without hangers swag between hangers. At boxes, leave enough free length to trim cleanly and set the connector straight, then cap the unused knockout to control smoke spread.

Where ceiling height or access makes work awkward, prefab short whips with connectors installed and tested. Tag circuit numbers at pull time so panel schedules match without guesswork later.

Bending, Cutting, And Terminating Cleanly

Measure your bend with the outside diameter in mind. The inner-edge radius for interlocked armor must be at least seven times that diameter. Mark the bend point, form a smooth arc by hand for small sizes, or use a roller bender for large feeders. Kinks or flat spots call for a new piece.

Cut armor with a purpose-built tool so the knife rides the valley and the conductors stay clear. Spin, snap, and twist off the ring. For jacketed types, score the jacket first to avoid tearing. Deburr, slide on the connector, and seat the anti-short bushing only if the fitting design needs it. Torque locknuts and screws to spec.

Sizing Conductors And Derating

Most branch MC uses THHN/THWN-2 copper at 90 °C insulation rating. Ampacity still ties to the terminal temperature limits and the count of current-carrying conductors in the cable. When more than three current-carrying conductors share a cable, apply adjustment factors. Neutral conductors on non-linear loads may count, based on the load type. Long runs may need a voltage-drop check, so feeders often step up in size to hold the drop in range.

Large aluminum MC feeders with XHHW-2 conductors cut weight and cost on long paths. Use antioxidant on aluminum terminations if the lugs call for it, and watch bend space in cabinets when armor diameter grows.

Spacing, Hangers, And Protection

Fasten MC so the cable carries its own weight. Typical spacing is 6 ft between hangers, with a strap or clamp within 12 in. of each box for small sizes. Horizontal runs bored through framing count as held when the hole spacing meets the 6 ft rule. Where the cable crosses sharp sheet-metal, add an edge guard.

In exposed runs near forklifts or ladders, shield the cable with channel, guard plates, or strut. Keep clearances from hot piping. In elevator hoistways and similar spaces, use raceway unless the listing and the local code say cable is allowed.

Quick Rules And Numbers

Common Mistakes To Avoid

Mixing fittings. EMT connectors are not MC connectors. The wrong ferrule or locknut loosens, cuts the armor, or breaks ground continuity.

Cranking bends too tight. Shortcuts here flatten the armor and bruise insulation. If space is tight, use a box set or a preformed elbow rated for the job.

Skipping pull planning. Long feeder pulls need reels, rollers, and a bending plan. Pulling a large cable around a rough edge ruins a day and a budget.

Ignoring sunlight or wet ratings. Roof runs need sunlight-resistant jackets. Garage runs need wet-location conductors. Match the product stamp to the space.

MC Cable For Lighting Controls

MC-PCS pairs branch power with a low-voltage control pair inside one armor. The control conductors arrive jacketed or separated by a divider, which keeps the control class intact with the power class in the same cable. Crews love it for 0–10V dimming, relay control, and sensor leads. Follow the color scheme on the drawings so control pairs stay consistent across rooms.

At fixtures with tight canopies, measure twice before ordering whip lengths. Few things slow a punch list like control loops that can’t reach the driver compartment.

Choosing Armor, Jacket, And Conductors

Pick armor to match the space. Aluminum interlocked armor keeps weight down and bends easily, which helps above ceilings and across long spans. Steel armor handles bumps a bit better around busy corridors and loading areas. Where chemicals or washdown live, stainless or copper armor pairs with matching fittings. For sun, water, or rooftop heat, a PVC jacket over the armor adds a layer that takes abuse before the metal sees it.

For conductors, THHN/THWN-2 copper is the day-to-day choice for branch runs. XHHW-2 shows up in long feeders thanks to better pull glide and high-temp rating. When the spec allows aluminum, big feeders often pencil out with XHHW-2 aluminum conductors because reels ship light and install fast. Color code to the plan, and leave printed phase tape in the panel for quick changes during trim.

Prepping Boxes And Devices

Shallow boxes and wide MC are a bad mix. If the device wall is tight, move to a deeper box or stack a ring so the connector sits flat and the armor clears the clamp. Use anti-short bushings only when the connector design lacks an internal insulator. Snap bushings in place firmly so they don’t ride up the conductor jacket during tightening.

When landing the ground, cut to reach with a smooth sweep, not a stiff spear. Bond to the box when the device or the local rules call for it, and keep the pigtail length short enough that the yoke seats without stress. At luminaires, confirm canopy depth before ordering whip lengths so the ferrule and locknut don’t crowd the driver.

Quick Inspection Checklist

• Hanger spacing meets the 6 ft rule, and a strap lands within 12 in. of each box.
• Bends show smooth arcs with no flats or kinks; large sizes formed with rollers.
• Connectors list for MC and match the armor and jacket; locknuts tight.
• Grounding conductor present and continuous; bonding jumpers where needed.
• Jacketed MC used where water or sun exists; markings readable at pull points.
• MC-HL only where classified space exists, with HL fittings to match.

Budget And Productivity Tips

Stage reels near the work face and use payoff jacks so armor doesn’t twist. Label home-run bundles with heat-shrink sleeves that carry circuit numbers and panel names. For repeat rooms, build kits: a whip, a device, the plate, and the screws in one bag. Write the length on the bag and a crew can rough a floor in steady rhythm.

Troubleshooting On Site

If a circuit trips on energizing, check the armor cut first. A deep score can nick a jacket at the edge. Open the connector, slide back the armor, and look for a crescent on the insulation. If the ground reads high resistance, chase loose locknuts and verify the grounding conductor at each box. On MC-PCS, mixed control colors cause dimming chaos; fix by tracing the pair from the driver to the first junction and matching the color set room by room.