Article 330 Metal-Clad Cable of Type MC [PDF]

Article 330 of the National Electrical Code (NEC) covers Metal-Clad Cable, commonly referred to as Type MC cable. Type MC cable is a versatile wiring method used in various electrical installations. Keep in remember MC means Metal Clad.

Article 330 Metal-Clad Cable of Type MC

NEC Article 330.6 Listing Requirements

According to this section of Article 330 in the National Electrical Code (NEC), Type MC cable must meet specific listing requirements. Here’s what this section entails:

Type MC Cable Listing: Type MC cable, which stands for Metal-Clad Cable, must undergo a listing process. This means that the cable’s manufacturer must have the cable tested and evaluated by a recognized and accredited testing laboratory or organization. The purpose of this listing is to ensure that the Type MC cable complies with safety and performance standards established by the NEC.
Listed Fittings: In addition to the cable itself, any fittings or connectors used to connect Type MC cable to electrical boxes, cabinets, or other equipment must also be listed and identified for such use. This ensures that the fittings are suitable for connecting Type MC cable and do not compromise the integrity or safety of the electrical installation.

NEC Article 330.10 Uses Permitted

330.10 Uses Permitted

This section of Article 330 in the National Electrical Code (NEC) outlines the various permitted uses for Type MC (Metal-Clad) cable. Type MC cable is versatile and can be employed in a range of electrical applications, subject to certain conditions. Here’s a breakdown of the permitted uses:

(A) General Uses:

Services, Feeders, and Branch Circuits: Type MC cable can be used for services, feeders, and branch circuits, making it suitable for distributing electrical power within a building.
Power, Lighting, Control, and Signal Circuits: It is permitted for use in power, lighting, control, and signal circuits, allowing it to carry a variety of electrical loads and functions.
Indoor or Outdoor Use: Type MC cable is suitable for both indoor and outdoor installations, providing flexibility in various environmental conditions.
Exposed or Concealed: It can be installed either exposed, where the cable is visible, or concealed within walls, ceilings, or conduit.
Direct Burial: Type MC cable can be directly buried in the ground when it is identified for such use. This is useful for outdoor installations where burying the cable is necessary.
Cable Tray: It is permitted for installation in cable trays, making it suitable for organized cable management systems.
Raceways: Type MC cable can be installed in any raceway, such as conduit or tubing, facilitating protection and routing.
Aerial Cable on a Messenger: When used as an aerial cable, it can be supported by a messenger wire, which is a support cable.
Hazardous (Classified) Locations: It can be used in hazardous locations where specifically allowed by other articles in the NEC. This ensures that it meets safety requirements for potentially dangerous environments.
Dry Locations and Embedded in Plaster Finish: In dry locations and when embedded in plaster finishes on materials like brick or masonry, it can be used. However, it should not be used in damp or wet locations unless specific conditions are met.
Damp or Wet Locations: In damp or wet locations, Type MC cable can be used if it has a corrosion-resistant jacket over the metallic covering and meets certain criteria, ensuring safe operation in wet environments. Phase conductors should be grouped together to minimize induced voltage on the sheath when single-conductor cables are used.

(B) Specific Uses:

Type MC cable is also permitted for specific uses, which are covered in more detail in other sections of the NEC, including:

Cable Tray: Type MC cable installed in a cable tray must comply with specific requirements outlined in various sections of the NEC.
Direct Buried: When directly buried, Type MC cable must adhere to either Article 300.5 or 305.15, depending on the circumstances.
Installed as Service-Entrance Cable: It can be used as service-entrance cable in accordance with Article 230.43, which addresses requirements for service conductors and equipment.
Installed Outside of Buildings or as Aerial Cable: When used outside of buildings or as aerial cable, Type MC cable must meet the conditions specified in Articles 225.10, 396.10, and 396.12.

It’s important to note that this list of permitted uses is not exhaustive, and other specific requirements and conditions may apply depending on the installation and local regulations. Compliance with the NEC ensures the safe and reliable use of Type MC cable in various electrical applications.

NEC Article 330.12 Uses Not Permitted

Article 330 of the National Electrical Code (NEC) outlines the uses that are not permitted for Type MC (Metal-Clad) cable. Type MC cable is versatile but should not be used under certain conditions to ensure safety and proper operation. Here are the conditions under which Type MC cable use is not permitted:

Subject to Physical Damage: Type MC cable should not be used in locations where it is subject to physical damage. This restriction is in place to prevent the cable from being crushed, pierced, or otherwise compromised, which could lead to electrical faults or hazards.
Exposure to Destructive Corrosive Conditions: Type MC cable should not be exposed to destructive corrosive conditions, unless specific protective measures are taken. These conditions include:
- a. Direct Burial in the Earth or Embedded in Concrete: Type MC cable should not be directly buried in the earth or embedded in concrete unless it is specifically identified and marked for direct burial. When buried in these environments, the cable must be designed to withstand the conditions it encounters.
- b. Exposure to Cinder Fills: Type MC cable should not be exposed to cinder fills, as cinder materials can be abrasive and corrosive, potentially damaging the cable over time.
- c. Strong Chlorides: Exposure to strong chlorides, such as those found in certain chemicals or environments, can corrode the cable’s components and compromise its integrity.
- d. Caustic Alkalis: Type MC cable should not be exposed to caustic alkalis, which are strong bases that can chemically attack the cable’s materials.
- e. Vapors of Chlorine or Hydrochloric Acids: Vapors from chlorine or hydrochloric acids can be corrosive and harmful to the cable’s components.

To ensure safety and compliance with the NEC, it is essential to follow these restrictions when considering the use of Type MC cable. Adhering to these guidelines helps prevent potential damage, electrical hazards, and operational issues associated with Type MC cable installations. Always consult the NEC and local electrical codes for specific requirements and regulations in your area.

NEC Article 330.15 Exposed Work

In accordance with Article 330 of the National Electrical Code (NEC), which covers Metal-Clad (MC) cable, there are specific guidelines for how MC cable should be installed in exposed work. Exposed runs of MC cable should be installed with the following considerations:

Closely Follow Surface: Exposed runs of MC cable should closely follow the surface of the building finish or running boards. This means that the cable should be secured and routed along the surface of walls or other building structures in a neat and orderly manner.
Underside of Joists: Exposed runs of MC cable are also permitted to be installed on the underside of joists. However, there are specific requirements for this installation method:a. Support at Each Joist: The cable must be supported at each joist it runs under. This support ensures that the cable remains in place and does not sag or become loose.b. Protection from Physical Damage: The cable should be located in a way that protects it from physical damage. This means that it should not be exposed to situations where it could be easily bumped, struck, or otherwise compromised.

NEC Article 330.17 Through or Parallel to Framing Members

In compliance with Article 330 of the National Electrical Code (NEC), which deals with Metal-Clad (MC) cable, when MC cable is installed through or parallel to framing members, specific protection measures must be observed. These measures are outlined in accordance with NEC requirements:

Protection against Physical Damage: MC cable installed through or parallel to framing members must be protected against physical damage in accordance with NEC sections 300.4(A), (C), and (D). This means taking steps to safeguard the cable from any potential harm or impact that could occur during or after installation.a. 300.4(A): Protection from Nails and Screws: Cable must be positioned and secured in a way that prevents penetration by nails, screws, or other fasteners used in the building’s construction. This helps avoid unintentional damage to the cable.b. 300.4(C): In Metal Studs: If MC cable is installed through or parallel to metal framing members, it should be protected by a guard plate to prevent damage from screws or nails driven into the studs. This protection ensures the cable’s integrity within metal stud constructions.c. 300.4(D): Where Subject to Physical Damage: In any location where MC cable is subject to physical damage, additional protective measures should be taken as necessary to maintain its safety and functionality.

NEC Article 330.23 In Accessible Attics

330.23 In Accessible Attics

When installing Type MC cable in accessible attics or roof spaces, specific requirements outlined in NEC 320.23 must be adhered to. These requirements are in place to ensure safe and compliant installations in these environments. Here’s what you need to know:

1. Accessible Attics and Roof Spaces: The term “accessible attics” refers to those attic spaces that can be entered and where work may be performed. Roof spaces accessible for maintenance or installation purposes are also included in this category.

2. Compliance with 320.23: In addition to adhering to Article 330, which deals with Metal-Clad (MC) cable, installers must also comply with the requirements outlined in NEC 320.23. This section of the code covers the installation of Types AC and MC cables specifically in accessible attics.

3. Ensuring Safety: These requirements are in place to ensure the safety of installations in attic and roof spaces, where conditions can vary and present unique challenges. Compliance with NEC standards helps mitigate potential risks associated with electrical installations in these areas.

4. Consult Local Codes: It’s important to note that while the NEC provides general guidelines for electrical installations, local electrical codes may include additional or more specific requirements. Always consult with local authorities and adhere to any applicable local codes when performing electrical work.

NEC Article 330.24 Bending Radius

330.24 Bending Radius for Type MC Cable

Properly bending Type MC (Metal-Clad) cable is essential to prevent damage and maintain the integrity of the electrical installation. The National Electrical Code (NEC) provides specific guidelines for bending radius based on the type and size of the cable. Here’s an overview of the bending radius requirements for Type MC cable:

(A) Smooth Sheath:

For Type MC cable with a smooth sheath and an external diameter of up to 19 mm (3/4 inch), the minimum bending radius should be ten times the external diameter of the metallic sheath.
For Type MC cable with a smooth sheath and an external diameter between 19 mm (3/4 inch) and 38 mm (1 1/2 inches), the minimum bending radius should be twelve times the external diameter of the metallic sheath.
For Type MC cable with a smooth sheath and an external diameter exceeding 38 mm (1 1/2 inches), the minimum bending radius should be fifteen times the external diameter of the metallic sheath.

(B) Interlocked-Type Armor or Corrugated Sheath:
For Type MC cable with interlocked-type armor or a corrugated sheath, the minimum bending radius should be seven times the external diameter of the metallic sheath.

(C) Shielded Conductors:

For Type MC cable with shielded conductors, the minimum bending radius should be twelve times the overall diameter of one of the individual conductors.
Alternatively, for multiconductor Type MC cable with shielded conductors, the minimum bending radius should be seven times the overall diameter of the entire cable, whichever value is greater.

Adhering to these bending radius requirements helps ensure that Type MC cable is bent without damaging the cable or its components. Proper bending practices are crucial for maintaining electrical safety and system reliability in various applications.

NEC Article 330.30 Securing and Supporting

330.30 Securing and Supporting of Type MC Cable

Properly securing and supporting Type MC (Metal-Clad) cable is crucial to maintain electrical safety and system reliability. The National Electrical Code (NEC) provides guidelines for the securement and support of Type MC cable. Here’s an overview of these requirements:

(A) General:

Type MC cable shall be supported and secured using approved methods that will not damage the cable. This includes the use of staples, cable ties listed and identified for securement and support, straps, hangers, or similar fittings.
Type MC cable fittings are permitted as a means of cable support.

(B) Securing:

Type MC cables shall be secured at intervals not exceeding 1.8 meters (6 feet), unless otherwise permitted in the NEC.
Cables containing four or fewer conductors, sized no larger than 10 AWG, shall be secured within 300 mm (12 inches) of every box, cabinet, fitting, or other cable termination.
In vertical installations, listed cables with ungrounded conductors 250 kcmil and larger shall be permitted to be secured at intervals not exceeding 3 meters (10 feet).

(C) Supporting:

Type MC cables shall be supported at intervals not exceeding 1.8 meters (6 feet), unless otherwise permitted in the NEC.
Horizontal runs of Type MC cable installed in wooden or metal framing members or similar supporting means shall be considered supported and secured when the support intervals do not exceed 1.8 meters (6 feet).

(D) Unsupported Cables:
Type MC cable shall be permitted to be unsupported and unsecured under certain conditions:

When the cable is fished between access points through concealed spaces in finished buildings or structures, and supporting is impractical.
When the cable is not more than 1.8 meters (6 feet) in length from the last point of cable support to the point of connection to luminaires or other electrical equipment, and both the cable and the point of connection are within an accessible ceiling.
When the cable is Type MC of the interlocked armor type, and its lengths do not exceed 900 mm (3 feet) from the last point where it is securely fastened. This is typically used to connect equipment where flexibility is necessary to minimize the transmission of vibration or to provide flexibility for equipment that may require movement after installation.

NEC Article 330.31 Single Conductors

When installing single-conductor cables with a nonferrous armor or sheath, certain installation requirements must be followed in accordance with the National Electrical Code (NEC), specifically section 300.20. Here’s what you need to know:

Single-Conductor Cables: These are cables that consist of a single insulated conductor enclosed within a nonferrous (non-iron) armor or sheath.

Installation Requirement:

The installation of single-conductor cables with nonferrous armor or sheath must comply with the requirements outlined in NEC section 300.20.

NEC Article 330.80 Ampacity

330.80 Ampacity of Type MC Cable

The ampacity of Type MC cable, as defined by the National Electrical Code (NEC), is determined by specific rules and considerations. Ampacity refers to the maximum current-carrying capacity of a conductor or cable. Here are the key points regarding the ampacity of Type MC cable:

(A) General Ampacity Determination:

For conductors with a size of 14 AWG (American Wire Gauge) and larger, the ampacity of Type MC cable shall be determined in accordance with the guidelines provided in either NEC section 310.14 or 315.60.
For smaller conductors with sizes of 18 AWG and 16 AWG, the ampacity is determined based on the tables provided in NEC Table 402.5.
The installation must not exceed the temperature ratings of terminations and equipment, ensuring that the entire system operates within safe temperature limits.

(B) Type MC Cable Installed in Cable Tray:

When Type MC cable is installed within a cable tray, the ampacity determination shall follow the guidelines outlined in NEC section 392.80.

(C) Grouping of Single Type MC Conductors:

When single Type MC conductors are grouped together in a triangular or square configuration and are installed on a messenger or exposed with a maintained free airspace (clearance) of not less than 2.15 times one conductor diameter (2.15 × O.D.) of the largest conductor within the configuration and adjacent conductor configurations or cables, specific ampacity limits apply.
The allowable ampacities for these grouped conductors are determined based on the following tables:

Table 310.20 for conductors rated from 0 volts through 2000 volts.
Table 315.60(C)(1) and Table 315.60(C)(2) for conductors rated over 2000 volts.

(D) Thermal Insulation:

In cases where more than two Type MC cables containing two or more current-carrying conductors are installed in contact with thermal insulation, caulk, or sealing foam without maintaining spacing between the cables, the ampacity of each conductor must be adjusted according to Table 310.15(C)(1).

Part III Construction Specifications

NEC Article 330.104 Conductors

The National Electrical Code (NEC) provides specific requirements for the minimum conductor sizes allowed for various applications in Type MC (Metal-Clad) cable. These requirements ensure safe and reliable electrical installations. Here are the key points regarding conductor sizes for Type MC cable:

(A) Conductor Sizes for Power and Grounding Conductors:

For ungrounded, grounded, and equipment grounding conductors in Type MC cable, the minimum allowable conductor sizes are as follows:
- 14 AWG (American Wire Gauge) for copper, nickel, or nickel-coated copper conductors.
- 12 AWG for aluminum or copper-clad aluminum conductors.

(B) Conductor Sizes for Control and Signal Conductors:

Control and signal conductors, which are typically used for low-voltage and data transmission applications, must meet different minimum size requirements in Type MC cable:
- 18 AWG for copper, nickel, or nickel-coated copper conductors.
- 14 AWG for copper-clad aluminum conductors.
- 12 AWG for aluminum conductors.

NEC Article 330.108 Equipment Grounding Conductor

When Type MC (Metal-Clad) cable is utilized to provide an equipment grounding conductor in an electrical installation, it must meet specific requirements outlined in the National Electrical Code (NEC) for equipment grounding conductors. Here’s what you need to know:

Compliance with NEC Sections: The equipment grounding conductor within Type MC cable must comply with the following NEC sections:
- 250.118(A)(10): This section specifies the types of conductors that can serve as equipment grounding conductors. Type MC cable used for this purpose must meet the criteria set forth in this section.
- 250.122: This section provides general requirements for equipment grounding conductors, including sizing and installation practices. Type MC cable used as an equipment grounding conductor must adhere to these guidelines.

NEC Article 330.112 Insulation

This section is about NEC article 330.112 Insulation Requirements for Type MC Cable.

Type MC (Metal-Clad) cable contains insulated conductors that must adhere to specific insulation requirements as outlined in the National Electrical Code (NEC). These requirements vary depending on the voltage level. Here’s a breakdown of the insulation requirements:

(A) 1000 Volts or Less:
For Type MC cables with a voltage rating of 1000 volts or less, the insulation of control and signal conductors in sizes 18 AWG and 16 AWG must meet the following criteria:

The insulation type used for these conductors must be listed in Table 402.3.
The insulation must have a maximum operating temperature not less than 90°C (194°F).
The selection of insulation must also comply with the provisions of NEC 724.49 when applicable.

Additionally, for Type MC cable conductors that are ungrounded, grounded, or equipment grounding conductors and are 16 AWG or larger in size, the insulation must meet one of the following requirements:

It must be of a type listed in Table 310.4(1).
It must be a type specifically identified for use in Type MC cable.

(B) Over 1000 Volts:
When Type MC cable is used for circuits exceeding 1000 volts, the insulated conductors must meet different requirements. Specifically, they must be of a type listed in both Table 310.4(2) and Table 315.10(A). This ensures that the insulation used in higher-voltage applications is suitable and rated for the specific conditions.

NEC Article 330.116 Sheath Requirements for Type MC Cable

The sheath of Type MC (Metal-Clad) cable plays a crucial role in providing protection, preventing corrosion, and ensuring the cable’s overall integrity. The National Electrical Code (NEC) specifies requirements for the sheath of Type MC cable, and here’s what you need to know:

Types of Metallic Sheath:
Type MC cable can have one of the following types of metallic sheath:

Smooth Metallic Sheath: This is a continuous, smooth metal covering that provides protection to the cable.
Corrugated Metallic Sheath: This type of sheath has a corrugated or ridged surface, adding strength and protection to the cable.
Interlocking Metal Tape Armor: Interlocking metal tape is used to form an armored sheath that surrounds the cable.

Continuous and Close Fitting:
The metallic sheath must be continuous, meaning it should form an unbroken covering around the cable. Additionally, it should be close fitting to the cable to ensure proper protection and shielding.
Nonmagnetic Sheath for Single Conductor Type MC:
In the case of single conductor Type MC cables, a nonmagnetic sheath or armor must be used. This nonmagnetic material is important to prevent interference with magnetic fields and maintain the cable’s performance.
Supplemental Corrosion Protection:
If the environment or conditions where the Type MC cable is installed require additional protection against corrosion, a supplemental outer covering of corrosion-resistant material can be used. This additional layer helps safeguard the cable from corrosion-related damage.
Sheath Not for Current-Carrying:
It’s important to note that the metallic sheath of Type MC cable should not be used as a current-carrying conductor. The sheath primarily serves protective and shielding purposes and should not be relied upon as a path for electrical current.

NEC Article 330.130 Hazardous (Classified) Locations

In hazardous or classified locations, where safety is of paramount importance, Type MC (Metal-Clad) cable must meet specific requirements to ensure its suitability and reliability. The National Electrical Code (NEC) outlines these requirements, particularly when Type MC cable is marked as MC-HL. Here’s what you need to know:

Listing Requirement: Type MC cable intended for use in hazardous (classified) locations and marked as MC-HL must be listed. This listing ensures that the cable complies with the safety and performance standards necessary for these environments.
Gas/Vapor Tight Continuous Corrugated Metallic Sheath: MC-HL cable must have a corrugated metallic sheath that is not only continuous but also gas/vapor tight. This tightness ensures that no gases or vapors can penetrate the cable sheath, reducing the risk of ignition or other safety hazards in areas where flammable substances may be present.
Overall Jacket of Suitable Polymeric Material: The cable should feature an overall jacket made of a suitable polymeric material. This jacket provides additional protection to the cable, enhances its durability, and helps maintain its integrity in challenging environments.
Separate Equipment Grounding Conductor: In hazardous locations, the cable must include a separate equipment grounding conductor. This conductor serves as an essential safety feature, providing a dedicated path for fault currents to ensure the protection of equipment and personnel.
MC-HL Marking: To clearly identify the cable’s suitability for hazardous locations, it must be marked as MC-HL. This marking informs installers and inspectors that the cable is intended for use in environments where explosive gases or vapors may be present.

Article 330 Metal-Clad Cable of Type MC [PDF]