MC Cable Installation: Securing and Strapping per NEC 330

Understanding Securing vs. Supporting in NEC 330.30

A frequent point of confusion in MC wiring is the difference between “securing” and “supporting.” The NEC handbook makes a clear distinction that is critical for compliance. Supporting refers to carrying the weight of the cable, preventing it from sagging under its own weight over a long run. A cable draped over a ceiling joist or laid in a cable tray is considered supported. Securing, however, involves physically fastening the cable to a structural member to prevent movement. This is typically done with MC cable straps, clamps, or listed cable ties. Proper securing is vital for conductor protection at termination points, as it prevents strain on connectors and conductors. According to NEC 330.30(A), any fitting used, whether it’s a staple, strap, or hanger, must be “designed and installed so as not to damage the cable.”

The 6-Foot Rule: MC Cable Support Intervals

The general guideline for supporting Type MC cable is what’s commonly known as the 6-foot rule. As detailed in NEC 330.30(C), MC cable must be supported at intervals not exceeding 6 feet (1.8 meters). This rule applies to both horizontal runs and vertical installations, although some exceptions exist. For horizontal runs that pass through holes in framing members like studs or joists, the framing itself is considered adequate support, provided the spacing between the members does not exceed 6 feet. This is a key difference from NEC conduit support requirements, which are often more stringent and vary by the type and size of the conduit. For example, EMT conduit generally requires support every 10 feet and within 3 feet of a termination. Adhering to these support intervals is a basic item on any electrical rough in checklist.

The 12-Inch Rule: Securing MC Cable at Terminations

While the 6-foot rule covers the main cable run, a more specific rule applies at termination points. NEC 330.30(B) mandates that for cables containing four or fewer conductors sized no larger than 10 AWG, the cable must be secured within 12 inches (300 mm) of every box, cabinet, fitting, or other termination. This 12-inch rule is crucial for preventing the weight of the MC wiring from putting physical stress on the listed fittings and internal conductors. The strap prevents the cable from being inadvertently pulled out of the connector or damaged. It’s important to note this rule’s specificity: it applies to common branch circuit sizes (10 AWG and smaller). For larger MC cables, this 12-inch securing requirement does not apply, though the general 6-foot support rule still does.

Choosing the Right MC Cable Straps and Supports

The code permits a variety of methods for securing and supporting MC cable, as long as they are installed correctly and do not damage the cable’s sheath. Common choices include:

• One-hole straps: These are quick to install and effective for securing a single cable run to a surface.
• Two-hole straps: Offering a more secure hold, these are ideal for larger cables or in areas subject to vibration.
• Cable Hangers and Stackers: These are efficient for supporting multiple horizontal runs, keeping the installation neat and organized.
• Cable ties for MC: Per NEC 330.30(A), cable ties for MC are permitted, but they must be “listed and identified for securement and support.” This means you cannot use just any zip tie; it must be specifically rated for this purpose, such as a Type 2S or 21S tie. Using non-listed ties is a common code violation.

When is Unsupported MC Cable Allowed? Exploring NEC 330.30(D)

There are specific scenarios where the standard rules for securing and supporting do not apply. These exceptions for unsupported cables, found in NEC 330.30(D), provide necessary flexibility for certain installation challenges. Type MC cable is permitted to be unsupported under the following conditions:

• Fished Installations: When the cable is “fished” through concealed, finished spaces (like an existing wall) where supporting it is impractical.
• Luminaire Whips: For a cable not more than 6 feet long from its last point of support to a luminaire or other electrical equipment within an accessible ceiling. In this case, the MC cable fitting itself can be considered a means of support. For professionals working with lighting, understanding how 2023 NEC updates protect NM and NMC cable from physical damage can provide additional context on cable safety. Learn more about protecting cables from physical damage here.
• Flexibility for Equipment: For interlocked armor-type MC cable in lengths up to 3 feet from the last secure point to connect equipment that requires movement or to minimize vibration transmission.

Step-by-Step Guide for Securing Horizontal and Vertical Runs

A systematic approach ensures that every MC cable installation is code-compliant and professional. Follow this process for a typical installation:

1. Plan the Cable Route: Determine the most direct and protected path for the cable, avoiding areas where it may be subject to physical damage.
2. Secure at the Start: Before pulling the cable, install your first mc cable strap or support within 12 inches of the starting box or panel (if required for the cable size).
3. Mark Support Intervals: For horizontal runs, measure and mark your support intervals at a maximum distance of every 6 feet along the planned route.
4. Install Supports: Fasten your chosen supports (e.g., one-hole straps, two-hole straps) at the marked intervals. For vertical installations, ensure the cable is supported at intervals not exceeding 6 feet, as required for all Type MC cable runs.
5. Install the Cable: Lay the cable into the supports. If using straps, fasten them securely but do not overtighten, as this could damage the cable’s armor and violate NEC 330.30(A).
6. Secure at the End: Secure the cable within 12 inches of the final termination box, cabinet, or fitting as required by the 12-inch rule.
7. Final Inspection: Walk the entire run to ensure no support intervals exceed 6 feet and that all termination points are properly secured. Staying current with installation rules is crucial; for example, recent NEC updates have changed NM and NMC cable installation rules, which can be reviewed here: 2023 NEC Updates for NM and NMC Cable.

For installations in attics, it’s also wise to review how armored cable guard strip requirements have been updated in the latest code cycle. Armored cable requirements in attics have changed, and staying informed is key. Ensure your installations are code-compliant with our detailed wiring methods courses.

Common Violations and Where Type MC Cable is Prohibited

Even with its versatility, there are clear limitations on where and how MC cable can be used. According to NEC 330.12, type MC cable is prohibited in locations where it is subject to physical damage, or exposed to destructive corrosive conditions unless specifically identified for such use. This includes direct burial in earth or concrete unless the cable is listed for that application. Common installation violations include exceeding the 6-foot support interval, failing to secure the cable within 12 inches of a box, and using non-listed plastic zip ties for support.

Primary Sources

• NFPA 70, National Electrical Code (NEC), Article 330

Frequently Asked Questions (FAQ)

What is the difference between securing and supporting MC wiring?

Supporting involves carrying the cable’s weight to prevent sagging, typically at 6-foot intervals. Securing means physically fastening the cable to prevent movement, which is required within 12 inches of most terminations to protect the connection.

Can I use plastic zip ties as mc cable straps?

You can only use cable ties for MC support if they are specifically “listed and identified for securement and support” per NEC 330.30(A). Standard, non-listed zip ties do not meet this requirement and should not be used as the primary means of support.

Does the 12-inch rule apply to all MC cable terminations?

No. The requirement to secure the cable within 12 inches of a termination specifically applies to Type MC cables with four or fewer conductors sized no larger than 10 AWG. Larger cables are exempt from this specific rule but must still adhere to the general 6-foot support requirement.

What are the NEC conduit support requirements compared to MC cable?

NEC conduit support requirements vary by conduit type but are generally stricter. For example, 1/2″ to 1″ EMT requires support every 10 feet and within 3 feet of each termination. In contrast, MC cable’s 6-foot rule offers more flexibility, contributing to its reputation for faster installation.