1.Structure and grounding conductor of MC cable
The basic structure of MC cable includes conductor, insulation layer, metal sheath, and external sheath (some models may not have external sheath). Its core feature is that the metal sheath can provide a certain degree of shielding, but whether it includes an independent grounding conductor depends on the specific model.
Usually, most MC cables contain independent grounding conductors, either bare copper or green insulated conductors, to provide a dedicated grounding path. However, there are also some MC cables that rely on their metal sheaths as grounding means, such as using aluminum or copper sheaths, which can be recognized as qualified grounding paths by NEC (National Electrical Code).
2.Grounding conductor configuration for MC cables of different specifications
1. 8 2 MC Wire
The 8 2 MC cable contains two No. 8 AWG insulated conductors, typically black and white, and is equipped with exposed or green insulated grounding conductors. Due to its larger conductor size, this cable is mainly used for high-power electrical equipment such as HVAC equipment, motors, and large lighting systems. Due to the high current requirements involved in the application of AWG cable No. 8, a separate grounding conductor must be included to ensure safe grounding.
2. Direct Burial MC Cable
Direct Burial MC Cable is a type of MC cable designed specifically for direct burial underground. This type of cable usually comes with a moisture-proof and corrosion-resistant outer sheath to adapt to the moisture and soil conditions in underground environments. Directly buried MC cables typically include a dedicated grounding conductor, supplemented by a metal sheath as an additional grounding shielding layer. This design ensures the safety of cables in underground environments while complying with NEC regulations.
3. 10 3 Metal Clad Wire
The conductor configuration of the 10 3 MC cable includes three No. 10 AWG insulated conductors (usually black, red, and white), plus an independent grounding conductor. Due to its smaller conductor size, this cable is typically used for medium power applications such as lighting, industrial equipment, and power branch circuits. In most cases, although the metal sheath of this cable provides some shielding effect, it cannot replace an independent grounding conductor. Therefore, 10 3 MC cables usually include a green insulated grounding wire.
4. 18 2 MC Cable
18 2 MC cable is a lightweight MC cable consisting of two 18 AWG conductors, primarily used for low-voltage control and signal transmission applications such as building automation systems, security systems, and fire alarm systems. Due to its application scenarios typically not involving high current loads, the cable may not include a dedicated grounding conductor and instead rely on a metal sheath for grounding. However, in certain specific applications, a separate grounding conductor may still be required to meet the requirements of NEC or local electrical regulations.
3.Grounding specifications and compliance of MC cables
The grounding requirements for MC cables in NEC specifications mainly depend on their application environment and specific model. Generally speaking:
1.If the metal sheath of the MC cable is recognized by NEC as an effective grounding path, a separate grounding conductor may not be required.
2.For MC cables with high current loads, such as 8 2 MC Wire and 10 3 MC Wire, an additional independent grounding conductor is usually required.
3.In direct burial or humid environments (such as Direct Burial MC Cable), grounding conductors are typically necessary to ensure the long-term safety and reliability of the system.
4.For low-voltage signal type MC cables, such as 18 2 MC cables, whether a separate grounding conductor is required depends on the specific application and regulatory requirements
