Romex (NM-B) vs MC Cable: Choosing the Right Wiring Method
Romex and MC cable both deliver electricity through copper conductors, but they are designed for fundamentally different installation environments. Choosing the wrong one can result in code violations, failed inspections, and safety hazards. Choosing the right one saves money where protection is unnecessary and provides protection where it is required. Here is a complete comparison to guide your selection.
What Is Romex (NM-B)?
Romex is the common trade name for NM-B (Non-Metallic sheathed cable, Type B). It consists of insulated copper conductors wrapped in a thermoplastic PVC outer jacket. The jacket is flexible, lightweight, and easy to handle. NM-B is the standard wiring method for residential construction throughout most of the United States. Common configurations include 14/2 NM-B for 15-amp lighting and outlet circuits, 12/2 NM-B for 20-amp kitchen, bathroom, garage, and outdoor circuits, 10/2 NM-B for 30-amp appliance circuits, and 14/3 and 12/3 NM-B for circuits requiring a third conductor.
What Is MC Cable?
MC (Metal Clad) cable consists of insulated THHN/THWN-2 conductors enclosed in an interlocking spiral armor jacket made of aluminum or galvanized steel. The metal armor provides physical protection, fire resistance, and a degree of electromagnetic shielding that the plastic NM-B jacket cannot match. Common configurations mirror NM-B: 14/2 MC, 12/2 MC, 10/2 MC, and 3-conductor versions.
Head-to-Head Comparison
Physical Protection
NM-B plastic sheath can be punctured by nails, screws, and staples during construction. It provides no protection against rodent gnawing, which is a common cause of electrical damage in attics and crawl spaces. MC cable armor resists nail penetration, rodent damage, and physical impact. For installations in areas where the cable may be exposed to damage, MC cable is the clear winner.
Fire Performance
MC cable metal armor maintains structural integrity longer in a fire than the NM-B plastic jacket, keeping conductors protected during the critical early minutes. This is one reason building codes require MC cable or conduit in commercial buildings, multi-family structures, and high-rise residential construction where fire containment between units is critical.
Installation Speed
NM-B is faster to install. It strips easily with a cable ripper, terminates with standard NM-B connectors, and bends freely through framing. MC cable requires a rotary cutter or MC cable stripper to cut the armor, anti-short bushings at every termination, and MC-specific connectors. Each MC cable termination takes 1 to 3 minutes longer than an NM-B termination, which adds up over a full project.
Cost
NM-B cable costs approximately 30% to 60% less per foot than MC cable of the same gauge and conductor count. A 250-foot spool of 12/2 NM-B costs significantly less than 250 feet of 12/2 MC. However, in applications where conduit would otherwise be required, MC cable can be less expensive than the combination of individual conductors plus conduit plus pulling labor.
Code Acceptance
NM-B is accepted in most residential construction nationwide, with notable exceptions including Chicago, parts of New York, and certain other jurisdictions that require MC cable or conduit for all installations. MC cable is accepted in virtually all applications nationwide: residential, commercial, industrial, and institutional. If you are unsure about local code requirements, MC cable is the universally safe choice.
When to Use Romex (NM-B)
Use NM-B for standard residential construction inside walls, ceilings, and floors in concealed locations. Use NM-B when your local code permits it and the installation is in a dry, protected environment. NM-B is the most cost-effective choice for the vast majority of residential wiring projects where the cable will be hidden behind drywall and protected from physical damage.
When to Use MC Cable
Use MC cable in commercial construction (offices, retail, restaurants, medical, institutional). Use MC cable for exposed residential runs (unfinished basements, garages, attics). Use MC cable in any jurisdiction that prohibits NM-B. Use MC cable in multi-family and high-rise residential construction. Use MC cable anywhere the wiring is subject to potential physical damage. Use MC cable when you want maximum protection regardless of code requirements.
Buying Romex and MC Cable
IB Lighting carries both NM-B (Romex) and MC cable in all standard gauges and configurations. We stock 12/2 and 14/2 NM-B, 12/2 MC, and other popular sizes from manufacturers including Southwire. Browse our electrical wire and cable selection for current pricing, or call (800) 674-9019 for contractor pricing on bulk orders. Free freight insurance included on every wire shipment.