Rigid Metal Conduit: Composition, Properties, and Applications

Rigid metal conduit (RMC) is a type of electrical raceway system used to protect and route electrical conductors in buildings and structures. It is primarily made of steel, providing strength and durability, and can also be made of stainless steel or aluminum for specific applications.

Wall Thickness and Coating

RMC has the thickest wall among steel raceways, offering excellent protection for electrical conductors and wiring systems. It can withstand mechanical stress, impact, and crushing forces better than other types of steel conduit. Galvanized rigid conduit (GRC) is a type of RMC that has a primary coating of zinc on both the exterior and interior surfaces. This coating provides corrosion resistance and protection against rust, making it suitable for use in harsh environments. Additionally, GRC may have a combination of zinc and nonmetallic coating for enhanced corrosion protection.

Electrical Code Compliance

Rigid metal conduit is covered by the National Electrical Code® (NEC) Article 344, which includes galvanized and stainless steel, aluminum, and red brass. Steel RMC is permitted in all atmospheric conditions and occupancies, making it a versatile choice for various electrical installations.

Trade Sizes and Threading

RMC is available in trade sizes ranging from 1/2 inch to 6 inches. It comes in 10-foot and 20-foot lengths and is threaded on both ends. One end has a coupling applied, while the other end has a color-coded thread protector. These thread protectors aid in product and trade size recognition during installation.

Corrosion Protection Options

Various coating options are available to protect galvanized steel RMC against corrosion. These include zinc, zinc-based, nonmetallic, or other alternate corrosion-resistant exterior coatings, as well as organic or zinc interior coatings. These coatings provide additional protection in corrosive environments, such as chemical plants, marine environments, and industrial facilities.

Applications of Rigid Metal Conduit

RMC is widely used in various electrical applications, including commercial, industrial, and residential buildings. It is commonly employed in the following scenarios:

• Exposed or concealed electrical installations
• Outdoor applications where weather resistance is crucial
• Underground installations where protection from moisture and soil conditions is required
• Industrial settings where mechanical protection against impact and crushing forces is necessary
• Hazardous locations where explosion-proof and corrosion-resistant conduits are mandated

Conclusion

Rigid metal conduit is a robust and reliable electrical raceway system that provides superior protection for electrical conductors. Its thick wall, galvanized coating, and various corrosion protection options make it suitable for a wide range of applications, from residential to industrial and hazardous environments. RMC complies with the NEC and is readily available in various trade sizes and lengths, making it a popular choice among electricians and contractors.

References

• NEMA: Steel Conduit & Electrical Metallic Tubing Section
• Steel Tube Institute: Rigid Metal Conduit
• EC&M: The Basics of Steel Conduit

FAQs

What is rigid metal conduit made of?

Rigid metal conduit (RMC) is primarily made of steel, providing strength and durability. It can also be made of stainless steel or aluminum for specific applications.

What are the advantages of using RMC?

RMC offers several advantages, including:

• Excellent mechanical protection for electrical conductors and wiring systems
• Resistance to impact, crushing forces, and vibration
• Corrosion resistance due to galvanized coating or additional protective coatings
• Compliance with NEC requirements for various electrical installations

What are the different types of RMC coatings?

RMC can have various coating options to enhance corrosion protection:

• Zinc coating: Provides basic corrosion resistance
• Zinc-based coating: Offers improved corrosion protection
• Nonmetallic coating: Suitable for specific corrosive environments
• Combination of zinc and nonmetallic coating: Provides enhanced protection

What are the common applications of RMC?

RMC is widely used in various electrical applications, such as:

• Exposed or concealed electrical installations
• Outdoor applications where weather resistance is crucial
• Underground installations for protection against moisture and soil conditions
• Industrial settings where mechanical protection is necessary
• Hazardous locations where explosion-proof and corrosion-resistant conduits are required

What are the trade sizes and lengths of RMC?

RMC is available in trade sizes ranging from 1/2 inch to 6 inches. It comes in standard lengths of 10 feet and 20 feet.

How is RMC installed?

RMC installation typically involves the following steps:

• Cutting the conduit to the desired length
• Threading the conduit ends
• Applying a coupling to one end and a thread protector to the other end
• Bending the conduit if necessary
• Securing the conduit to the wall or other supporting structure
• Pulling the electrical conductors through the conduit

What safety precautions should be taken when working with RMC?

When working with RMC, it is important to follow these safety precautions:

• Wear appropriate personal protective equipment (PPE), including gloves, safety glasses, and a hard hat
• Use proper tools and equipment for cutting, threading, and bending the conduit
• Be careful when handling sharp edges of the conduit
• Follow all electrical safety guidelines and regulations