12/4 MC cable is a metal-clad cable with four 12 AWG conductors, used for branch circuits that need extra switched legs or a neutral per phase.
Four current-carrying 12-gauge wires inside a flexible metal armor solve a specific wiring problem: getting more than the standard three conductors to a box without running conduit. The fourth conductor is what separates 12/4 from the common 12/2 and 12/3 spools, and it changes which jobs the cable fits.
What 12/4 MC Cable Actually Contains
Type MC cable is a factory assembly of one or more insulated circuit conductors enclosed in interlocking metal tape or a smooth or corrugated metallic sheath. NEC Article 330 covers its use, installation, and construction. Traditional Type MC is manufactured to UL 1569, and conductors run in sizes 18 AWG and larger.
The 12/4 designation breaks down simply: four 12 AWG conductors. Southwire product listings show color sets like black, red, blue, and white, plus a separate grounding conductor — often green or aluminum. Armor diameters on those listings run from roughly 0.544 in to 0.7 in depending on construction, with weights from 145 lbs per 1000 ft up to 293 lbs per 1000 ft.
MC cable conductors can be copper, aluminum, or copper-clad aluminum. Interlocking metal tape armor requires a bare or insulated equipment grounding conductor in addition to the circuit conductors — that ground is not optional.
Where 12/4 MC Cable Gets Used
Four-conductor 12 AWG MC is common where multiple switched legs or multiwire branch-circuit style runs are needed. The extra conductor carries a second switched hot, a shared neutral arrangement, or a neutral per phase in 120/208V systems.
- Multi-switch lighting: one home run feeding several switch-controlled loads from a single box.
- Multiwire branch circuits: shared neutral configurations that 12/3 cannot cover.
- Commercial branch wiring: services, feeders, and branch circuits where the cable is permitted indoors, outdoors, exposed, or concealed.
- Neutral-per-phase setups: Southwire sells configurations named for 120/208V color coding, which tells you the intended system.
If you are comparing spools before a job, a tested breakdown of the common 12/4 options is worth a look before you order — see this roundup of 12 4 mc cable picks.
Installation Rules And Limits That Matter
MC cable must be secured within 12 in of every box or fitting and supported at intervals not exceeding 6 ft. That spacing applies to cables with four or fewer conductors no larger than 10 AWG — which is exactly where 12/4 lands.
Two limits trip people up. First, bend radius: for interlocked-armor or corrugated-sheath MC, the minimum bend radius is seven times the external cable diameter. On a 0.7 in armor, that is roughly 4.9 in. Second, location: MC is permitted in wet locations only when the construction meets NEC moisture requirements, which normally means a PVC jacket over the armor. Standard armored 12/4 without that jacket does not qualify.
MC is also not permitted where it is subject to physical damage or exposed to destructive corrosive conditions. Article 330’s minimum conductor size is 18 AWG copper, nickel, or nickel-coated copper, or 12 AWG aluminum or copper-clad aluminum — 12 AWG copper sits comfortably above that floor.
| Property | 12/4 MC Cable Spec | Why It Matters |
|---|---|---|
| Conductors | Four 12 AWG plus equipment ground | Extra leg or neutral per phase |
| Voltage rating | 600V on Southwire listings | Handles branch and feeder work |
| Armor diameter | About 0.544–0.7 in | Sets minimum bend radius |
| Weight | 145–293 lbs per 1000 ft | Affects pulling and support |
| Support spacing | Every 6 ft max | Strapping requirement |
| Box securing | Within 12 in | Termination requirement |
| Bend radius | 7x cable diameter | Prevents armor damage |
| Wet locations | Only with jacketed construction | Dry armor fails the rule |
Common Mistakes And What To Check First
The grounding conductor is the most frequent oversight. Interlocking tape armor does not substitute for it, so a 12/4 run still needs that fourth-plus wire terminated correctly at both ends.
Conductor color patterns vary by product. Southwire listings show black/red/blue/white with an aluminum ground on one SKU and black/red/blue/green on another, and one configuration uses orange in place of white. Match the pattern to your system before pulling wire, and confirm the armor jacket meets your location.
Expectations about price deserve an honest note: public listings for these products did not carry reliable published pricing when researched, so treat any figure you see as supplier-specific rather than standard.
That is the current article the sources cite, and it governs anything you install today.
References & Sources
- Southwire. “Armorlite Type MC THHN/THWN Circuit Size Copper Conductor — Neutral Per Phase” Product listing for conductor counts, color sets, armor diameters, and weights.
- EC&M. “NEC Art. 330 and MC Cable” Covers the Article 330 scope, construction, and minimum conductor sizes.
- EC&M. “Systems Review: Metal-Clad Cable Requirements” Supporting and securing intervals, bend radius, and location limits.
FAQs
Can 12/4 MC cable be used outdoors?
Only if the cable construction meets NEC moisture requirements for wet locations, which normally means a PVC jacket over the armor. Standard interlocking-armor MC without that jacket is limited to dry and damp conditions, and it is never permitted where it faces physical damage.
Does the metal armor count as the ground?
No. Interlocking metal tape armor requires a bare or insulated equipment grounding conductor inside the assembly, in addition to the circuit conductors. That ground must be terminated at both ends, which is why a 12/4 run involves more than four wires in practice.
How far apart do you secure it?
Secure the cable within 12 in of every box or fitting, and support it at intervals not exceeding 6 ft. Those intervals apply to cables with four or fewer conductors no larger than 10 AWG, which covers 12/4 installations directly.
