Armored Cable (MC/BX) Symbol
Definition: The Armored Cable (MC/BX) symbol represents a type of electrical wiring in which insulated conductors are enclosed within a flexible metallic sheath — either metal-clad (MC) or armored cable (BX/AC) — used in residential and commercial wiring diagrams to indicate a mechanically protected cable run between two points A and B, as described in NFPA 70 (National Electrical Code) Articles 330 (MC) and 320 (AC).
Also known as: metal clad cable, MC cable, BX cable, armored cable, AC cable, flex armored, flexible metal conduit cable.
What the Armored Cable (MC/BX) symbol means
The Armored Cable (MC/BX) symbol in a wiring diagram represents a cable assembly that provides physical protection to its enclosed conductors through a corrugated or interlocked metallic armour. In electrical wiring diagrams, the symbol distinguishes an armored cable run from a plain NM (Romex) cable or conduit run, indicating that the cable has built-in mechanical protection suitable for exposed locations, damp areas, or installations requiring a ground path through the metal sheath.
Armored cable appears frequently in commercial, industrial, and residential wiring diagrams for branch circuits, lighting feeds, and equipment connections. The symbol's two endpoints (A and B) represent the cable's termination points — typically a panel, junction box, or equipment enclosure at each end. MC cable includes a separate insulated equipment ground conductor; BX/AC cable may rely on the metal sheath as the grounding path (check local code).
How to identify the Armored Cable (MC/BX) symbol
The Armored Cable (MC/BX) symbol is drawn as a horizontal line between two pins (A on the left, B on the right) with a distinctive hatching, braided, or corrugated pattern overlaid on the line to indicate metallic armour. Some schematic tools show the symbol as a thick double line or a line with a wavy/spiral overlay representing the interlocked metal sheath. The symbol is typically labelled 'MC', 'BX', 'AC', or 'Armored Cable' with an annotation indicating wire gauge, conductor count, and voltage rating (e.g., '12/2 MC 600V').
Function in a circuit
Armored cable provides the same current-carrying function as any insulated conductor — delivering electrical power or signals between two points — while the metallic armour jacket protects the enclosed conductors from mechanical damage, crushing, rodent damage, and abrasion. MC cable (NEC Article 330) is listed for use in dry, wet, and damp locations (with appropriate listing) and is used in commercial buildings, healthcare facilities, and industrial plants. The metal armour of MC cable is bonded to ground at both ends via a listed MC connector, providing a low-impedance fault current path. BX/AC cable (NEC Article 320) is typically limited to dry locations and 10 ft or less of flexible whip runs.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60227 and IEC 60502 cover armoured cables internationally; IEC armoured cables use steel wire armour (SWA) or steel tape armour (STA) rather than the interlocked aluminium or steel of US MC/BX. IEC wiring diagrams typically show armoured cable as a line with a shield/braid notation or as part of a cable schedule table. |
|---|---|
| ANSI/IEEE 315 | ANSI/NFPA 70 (National Electrical Code) Article 330 defines Type MC (Metal-Clad Cable) and Article 320 defines Type AC (Armored Cable/BX). ANSI/IEEE 315-1975 does not provide a specific schematic symbol for armored cable; wiring diagram conventions for MC/BX are de-facto standards used by US electrical drawing tools. |
| Key difference | IEC armoured cable (SWA) uses separate galvanised steel wire or tape armour over standard insulated conductors and is common in the UK, Europe, and international installations. US MC/BX cable uses a flexible interlocked aluminium or steel armour strip and is governed by NEC Articles 320/330. The schematic symbol differs: IEC uses a cable-with-shield notation; US wiring diagrams use the hatched/armour-pattern line shown here. |
Terminals / pins
| Pin | Name |
|---|---|
| a | A |
| b | B |
Typical values
Common wire gauges: 14 AWG, 12 AWG, 10 AWG, 8 AWG; conductor counts: 2-wire (hot + neutral), 3-wire (hot + hot + neutral), 4-wire; voltage rating: 600 V AC (standard MC cable); temperature rating: 90°C (THHN/THWN insulated conductors inside); armour material: aluminium interlocked (most common), steel interlocked, or corrugated aluminium.
Where the Armored Cable (MC/BX) symbol is used
- Commercial office and retail branch circuit wiring where conduit is impractical but mechanical protection is required
- Healthcare facility wiring (hospitals, clinics) where MC cable meets the NEC healthcare occupancy requirements
- Industrial machinery connections providing flexible mechanical protection between fixed conduit and vibrating equipment
- Residential wiring in finished walls or exposed basement and garage locations needing protection beyond NM (Romex)
- Data centre power distribution where the metallic armour provides EMI shielding for sensitive low-voltage circuits
- HVAC equipment connections for thermostat wiring and low-voltage control circuits in damp locations
- Modular office systems (furniture feeds) using MC whip runs from ceiling distribution to workstation outlets
Example
In a commercial office lighting wiring diagram, MC cable runs from a junction box (point A) above the ceiling grid to a recessed light fixture (point B). The armored cable symbol shows the protected cable path; an annotation reads '12/2 MC 600V', indicating two 12 AWG conductors plus an equipment ground inside the metal armour. The MC connectors at both ends bond the armour to the metal junction box and fixture housing for fault current continuity.
Key facts
- Armored Cable (MC/BX) in US wiring diagrams refers to Type MC (NEC Article 330) or Type AC/BX (NEC Article 320) cable, which encloses insulated conductors in a flexible interlocked metal armour jacket.
- The schematic symbol has two pins: A (left) and B (right) representing the cable's termination points, connected by a line with a hatched or armour-pattern overlay indicating the metallic sheath.
- Type MC cable includes a separate insulated equipment grounding conductor inside the armour; Type AC/BX relies on the metal armour plus an internal bonding strip as the grounding path — a critical safety distinction.
- MC cable is listed for dry, damp, and wet locations (with appropriate jacket type) under NEC 330.10; Type AC cable is generally limited to dry locations under NEC 320.10.
- The metal armour of MC cable provides mechanical protection (crush, abrasion, rodent resistance) but is not a substitute for conduit in areas subject to severe physical damage.
- Armored cable conductors are typically insulated with 90°C THHN/THWN wire, giving the cable a 90°C temperature rating — higher than standard NM (Romex) rated at 60°C or 90°C.
- In wiring diagrams, armored cable runs are annotated with the conductor size (AWG), count (e.g., 12/3), and voltage rating (600 V) to fully specify the cable for installation.
- The international equivalent of MC/BX cable is SWA (Steel Wire Armoured) cable per IEC 60502, commonly used in the UK, Australia, and international installations.
Frequently asked questions
What does the armored cable symbol look like in a wiring diagram?
The armored cable symbol is a line between two endpoints (A and B) with a hatched, braided, or corrugated pattern along the line representing the metallic armour jacket. Some tools show it as a thick double line or a line with a spiral overlay. Labels such as 'MC', 'BX', or a wire gauge annotation (e.g., '12/2 MC') identify it as armored cable.
What does the MC or BX cable symbol mean in a wiring diagram?
The MC/BX cable symbol indicates a cable run where the conductors are enclosed in a flexible metallic armour for mechanical protection. It distinguishes this protected cable type from plain NM (Romex) cable or conduit runs, signalling that the circuit requires the additional physical protection provided by the interlocked metal sheath.
What is the difference between MC cable and BX cable?
Type MC (Metal-Clad, NEC Article 330) always includes a separate insulated equipment ground conductor inside the armour. Type AC (Armored Cable/BX, NEC Article 320) uses the metal armour itself plus an internal aluminium or steel bonding strip as the grounding path and is generally limited to dry locations. MC cable has broader applications including damp and wet locations with appropriate listing.
What standard covers armored cable in the US?
Armored cable in the US is governed by NFPA 70 (National Electrical Code): Article 330 covers Type MC (Metal-Clad Cable) and Article 320 covers Type AC (Armored Cable/BX). ANSI/IEEE 315 does not define a specific symbol for MC/BX; US wiring diagram tools use de-facto conventions for the armour-pattern line representation.
What is the international equivalent of MC/BX armored cable?
The international equivalent is Steel Wire Armoured (SWA) cable defined in IEC 60502 and BS 5467. SWA cable uses individual galvanised steel wires as armour rather than the interlocked aluminium strip used in US MC cable. SWA is common in the UK, Europe, Australia, and other IEC-standard countries for underground and industrial wiring.
Can armored cable be used outdoors or underground?
Type MC cable with a PVC or PE outer jacket listed for wet locations (Type MC-HH or MC-HL) can be used outdoors in exposed locations. However, standard MC cable without a listed outer jacket is not rated for direct burial or continuous immersion. Underground applications typically require Type UF cable or conductors in conduit. IEC SWA cable with a PVC oversheath is designed for direct burial.
What wire gauges are available for MC cable?
MC cable is available in conductor sizes from 18 AWG (for control wiring) to 2000 kcmil (for large feeders). Common residential and light commercial sizes are 14 AWG, 12 AWG, and 10 AWG for 15 A, 20 A, and 30 A branch circuits respectively. The armored cable symbol annotation (e.g., '12/2 MC') specifies the gauge and conductor count.
Place the Armored Cable (MC/BX) symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.