MC cable (Metal Clad Cable) is a frequently utilized wiring method in commercial, residential, and industrial settings due to its inherent protection, flexibility, and cost-effectiveness. Proper installation techniques are essential to ensure safety, performance, and adherence to National Electrical Code (NEC) standards. This article details the process of installing MC cable, covering necessary tools, step-by-step instructions, common pitfalls to avoid, and frequently asked questions.
Preparing for Installation
Before commencing installation, gathering the appropriate tools and materials is crucial. These include a rotary MC cable cutter or hacksaw, MC cable connectors (specifically listed for MC cable use), a wire stripper and pliers, screwdrivers, MC cable straps or staples, electrical tape and wire connectors (wire nuts), and personal protective equipment such as safety gloves and glasses.
Planning the cable route is the initial step. The planned path should avoid sharp edges or areas susceptible to mechanical damage. It is important to verify that the selected cable type—specifically whether it is designed for indoor use or features a PVC jacket—is appropriate for the intended environment.
Cutting and Stripping the MC Cable
The initial physical step involves cutting the MC cable to the required length. A rotary MC cable cutter is recommended for a clean cut. If a hacksaw is used, careful attention must be paid to avoid nicking the inner conductors. Standard wire cutters should be avoided as they can crush or deform the metal armor.
Following the cut, the metal armor must be carefully slid back to expose the inner conductors. An anti-short bushing, often referred to as a “redhead,” should be used to protect the wires from the sharp edges of the metal armor.
Installing Connectors and Making Electrical Connections
A proper MC cable connector must be attached to the cut end of the cable. The connector should be tightened securely to prevent movement or slippage. The cable is then inserted into an electrical box and fastened using the connector’s locknut.
Next, the insulation is removed from each conductor using a wire stripper. Care must be taken to avoid nicking or damaging the copper or aluminum wires. Electrical connections are made using wire connectors (wire nuts), ensuring correct color matching—black to black, white to white, and ground to ground. Electrical tape can be applied for additional security, if required.
Securing the Cable and Providing Protection
The MC cable must be securely fastened to framing or surfaces using cable straps or staples. These should be installed every six feet, as per NEC guidelines, and within 12 inches of each termination point. Over-tightening should be avoided to prevent crushing the armor.
In situations where the cable is exposed to potential damage, conduit or guard strips should be installed to provide additional protection. In fire-rated assemblies, fire-resistant sleeves or insulation should be used around the MC cable to maintain the integrity of the fire barrier.
Types of MC Cable
Several types of MC cable are available, each designed for specific applications. Standard MC cable features interlocking metal tape armor and is commonly used in general wiring applications. MC-HL cable is designed for hazardous locations and includes a gas/vapor-tight continuous corrugated metallic sheath. Jacketed MC cable has an additional PVC jacket, making it suitable for wet locations. Aluminum Interlocked Armor (AIA) MC cable offers flexibility and mechanical protection, often used in industrial settings. Continuously Corrugated Welded (CCW) MC cable provides superior protection against moisture and corrosive elements, making it ideal for harsh environments.
Installation Considerations and NEC Requirements
Adherence to NEC requirements is paramount during MC cable installation. The cable must be supported and secured at intervals not exceeding six feet and within 12 inches of each termination point, as specified in Article 330.30. Proper planning of the installation path is essential, ensuring it is clear of obstacles and sharp edges.
Final Inspection and Testing
A final inspection should be conducted to verify the integrity of the installation. All terminations should be checked to ensure they are tight and secure, as loose connections can lead to overheating or arcing. The support spacing should be confirmed to ensure the cable is properly supported along its entire length. If applicable, the circuit should be tested using a voltage tester or multimeter to verify correct wiring and functionality.
Common Installation Mistakes to Avoid
Several common mistakes can compromise the safety and reliability of an MC cable installation. These include using the wrong type of connector (only connectors approved for MC cable should be used), over-bending or kinking the cable, skipping the equipment grounding conductor connection, and using MC cable in direct burial without conduit (unless it is specifically rated for MC-DB).
MC Cable vs. Conduit Installation
Compared to installing individual wires inside a conduit, MC cable installation is generally faster and easier. This is because the metal armor provides both mechanical protection and serves as part of the grounding system, eliminating the need to pull wires through conduit.
Frequently Asked Questions
Several frequently asked questions address common concerns regarding MC cable installation. MC cable can be used outdoors, but only if it is PVC jacketed and rated for outdoor or wet conditions. The metal armor generally eliminates the need for conduit in most applications. There is no fixed length limit for MC cable runs, but voltage drop should be considered for long runs exceeding 100 feet. To terminate MC cable in a panel, secure the cable with a listed connector, strip the insulation, and connect the conductors to the correct lugs or breakers, ensuring proper grounding.
Conclusion
Installing MC cable requires careful attention to detail and adherence to NEC standards. By following the outlined steps, avoiding common mistakes, and utilizing the appropriate tools and materials, a safe, reliable, and compliant installation can be achieved. The metal armor provides inherent protection, simplifying the process compared to traditional conduit installations. Prioritizing safety and consulting the latest NEC standards or a licensed electrician when in doubt are crucial for a successful outcome.