MC armored cable specifications

MC (Metal Clad) cable is a power cable rated up to 600 V consisting of copper or aluminum conductors with thermoplastic insulation, a grounding conductor, a general binder tape assembly, and an interlocked aluminum or steel metal armor that provides mechanical protection and serves as an equipment grounding path. Its maximum operating temperature in dry conditions is 90 °C for copper conductors and 75 °C for aluminum, with an installation temperature range of -25 °C to 70 °C without an outer jacket.

Construction Specifications

Component	Material	Specification
Phase conductor	Soft copper or 8000 series aluminum	THHN/THWN-2, compressed or compact
Insulation	PVC plus nylon	Flame retardant, color per NEC code
Grounding conductor	Soft copper	Green insulation per NEC, size per Table 250.122
Assembly	Polypropylene or polyester tape	Covers insulated conductors, no absorbent filler
Armor	Aluminum alloy (AL 5052 or similar) or galvanized steel	Helical, interlocked, minimum thickness 0.56 mm / 0.022 in for standard sizes
Jacket (optional)	Flexible PVC	Sunlight and oil resistant, available in direct burial versions

Dimensions and Diameters

AWG/kcmil Size	Cross Section (mm²)	Nominal Outer Diameter Aluminum (mm / in)	Nominal Outer Diameter Steel (mm / in)
14 AWG solid	2.08 mm² / 4.11 kcmil	8.6 mm / 0.339 in	9.1 mm / 0.358 in
12 AWG solid	3.31 mm² / 6.53 kcmil	9.7 mm / 0.382 in	10.2 mm / 0.402 in
10 AWG solid	5.26 mm² / 10.38 kcmil	11.2 mm / 0.441 in	11.9 mm / 0.469 in
8 AWG	8.36 mm² / 16.5 kcmil	13.2 mm / 0.520 in	14.0 mm / 0.551 in
6 AWG	13.3 mm² / 26.2 kcmil	15.5 mm / 0.610 in	16.3 mm / 0.642 in
4 AWG	21.1 mm² / 41.7 kcmil	18.3 mm / 0.720 in	19.1 mm / 0.752 in
2 AWG	33.6 mm² / 66.4 kcmil	21.6 mm / 0.850 in	22.4 mm / 0.882 in
1/0 AWG	53.5 mm² / 105.6 kcmil	26.2 mm / 1.031 in	27.0 mm / 1.063 in

The outer diameter of a cable with stranded conductor is larger than that of a solid conductor of the same AWG size; the table indicates typical values for Class B or C conductors in aluminum armor without jacket.

Continuous Ampacity

Allowable current in copper conductors, 30 °C ambient temperature, maximum three current-carrying conductors in MC cable, installed in air.

AWG/kcmil Size	60 °C (A)	75 °C (A)	90 °C (A)
14 AWG	15 A	20 A	25 A
12 AWG	20 A	25 A	30 A
10 AWG	30 A	35 A	40 A
8 AWG	40 A	50 A	55 A
6 AWG	55 A	65 A	75 A
4 AWG	70 A	85 A	95 A
2 AWG	95 A	115 A	130 A
1/0 AWG	125 A	150 A	170 A

For aluminum conductors, apply a factor of 0.80 to the copper ampacity; the maximum operating temperature of aluminum in MC cable is typically limited to 75 °C.

Temperature Correction Factors

Ambient Temperature (°C / °F)	Factor for 60 °C	Factor for 75 °C	Factor for 90 °C
10 °C / 50 °F	1.29	1.20	1.15
20 °C / 68 °F	1.12	1.08	1.04
30 °C / 86 °F	1.00	1.00	1.00
40 °C / 104 °F	0.82	0.88	0.91
50 °C / 122 °F	0.58	0.75	0.82
60 °C / 140 °F	—	0.58	0.71
70 °C / 158 °F	—	—	0.58

Physical Properties and Resistances

Property	Value
Maximum conductor temperature (continuous operation)	90 °C / 194 °F (copper THHN), 75 °C / 167 °F (aluminum)
Maximum short circuit temperature	250 °C / 482 °F (max 5 s)
Installation temperature range	-25 °C to 70 °C / -13 °F to 158 °F (without jacket)
Compression resistance (aluminum armor)	450 N/cm / 257 lb/in minimum
Impact resistance	2.26 J / 20 lb·in minimum
Insulation resistance at 15.6 °C / 60 °F	Minimum 2000 MΩ·km at 500 V DC
Flammability class	UL 1569, FT4 (vertical cable tray)

Allowable Voltage Drop

The voltage drop for power installations using MC cable must be limited to 3% per branch circuit or 5% combined with the feeder per NEC 210.19. The formula for a single-phase AC system is:

Vd = (2 × L × I × R) / 1000

Variable	Meaning	Unit
Vd	Voltage drop	V
L	Circuit length (one way)	m
I	Load current	A
R	Electrical resistance of conductor	Ω/km

For three-phase systems, replace the factor 2 with √3 ≈ 1.732. Resistance values at 75 °C for copper are 8.28 Ω/km for 14 AWG, 5.21 Ω/km for 12 AWG, 3.28 Ω/km for 10 AWG, and 2.08 Ω/km for 8 AWG.

Typical Applications

MC armored cable is approved for the following applications per NEC 330:

• Branch circuits, feeder circuits, and control circuits in commercial, industrial, and multifamily residential buildings.
• Installation in cable trays, tray supports, ladder racks, or exposed on surfaces.
• Direct burial or installation in underground conduits when the cable has an approved PVC jacket (marked “MC direct burial”).
• Use in damp or wet locations if the cable includes a moisture-resistant jacket.
• Power supply for HVAC equipment, pumps, motors, electrical panels, and load centers in environments with moderate mechanical exposure.
• Not permitted in Class I Division 1 hazardous locations unless the cable has specific certification (MC-HL) and is installed with explosion-proof fittings.

Installation Accessories

Accessory Type	Function	Typical Material
“Push-in” / “snap-in” connector	Quick termination in metal box, spring retention	Zinc-plated steel, aluminum alloy
Compression connector	Termination in enclosure with tight seal and electrical continuity	Anodized aluminum, stainless steel
Anti-short bushing (red devil bushing)	Protection of conductors against sharp armor edge	Polypropylene, nylon
Cable clamp	Securing cable along its run every 1.8 m / 6 ft maximum	Steel, aluminum
Outdoor termination kit	IP65 environmental seal with cable gland	Nickel-plated brass or stainless steel

Frequently Asked Questions (FAQ)

What is the ampacity of a 12 AWG copper MC cable at 75 °C?

The ampacity of a 12 AWG copper MC cable with THHN insulation at 75 °C is 25 A, provided that there are no more than three current-carrying conductors and the ambient temperature does not exceed 30 °C / 86 °F.

Can MC cable be installed directly underground without additional protection?

Standard MC cable is not suitable for direct burial; it requires the version with PVC jacket marked “MC direct burial”, which withstands moisture and soil chemical attack, with a minimum installation temperature of -25 °C / -13 °F.

What is the maximum temperature a THHN conductor inside an MC cable can withstand during a short circuit?

The copper conductor inside an MC cable with THHN insulation can reach 250 °C / 482 °F during a short circuit, with a maximum duration of 5 seconds without compromising insulation integrity.

What is the smallest size manufactured for MC cable?

MC cable is typically manufactured from 18 AWG / 0.82 mm² for control and signaling circuits, and from 14 AWG / 2.08 mm² for power circuits of 120 V and above.

What is the thickness of the aluminum armor on a 10 AWG MC cable?

The aluminum armor on a 10 AWG MC cable has a nominal thickness of 0.56 mm / 0.022 in, providing an approximate outer diameter of 11.2 mm / 0.441 in in a three-conductor plus insulated ground configuration.

How much does a 4/3 copper MC cable with steel armor weigh per meter?

A 4 AWG 3-conductor copper plus ground MC cable with galvanized steel armor weighs approximately 0.89 kg/m / 0.60 lb/ft; the aluminum armor version reduces the weight to about 0.62 kg/m / 0.42 lb/ft.

References

• engineeringtoolbox.com: https://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html
• southwire.com: https://www.southwire.com/wire-cable/metal-clad-cable/c/c-mcmain