How to Install RGS Conduit: A Step-by-Step Professional Guide

Understanding RMC: Beyond the Basic Conduit Meaning

For licensed electricians, the term “conduit” encompasses a wide range of products, but Rigid Metal Conduit (RMC) stands in a class of its own. When discussing conduit meaning in a professional context, RMC (rigid metal conduit) refers to a heavy-walled, threaded electrical raceway made of steel with a protective zinc coating. Governed by NEC Article 344, this type of raceway is recognized for providing the highest level of physical protection against impact and damage. The robust nature of RMC electrical conduit makes it the standard for industrial applications, outdoor installations, and areas where physical abuse is a significant concern. Its threaded joints, assembled with listed fittings and installed per manufacturer and code guidance, help deliver mechanical strength and continuity for grounding where permitted.

IMC vs RMC Conduit: Making the Right Choice

A common point of discussion in the field is the IMC vs RMC conduit debate. While both are rigid metal conduits, they have key differences. RMC has a thicker wall and is heavier than Intermediate Metal Conduit (IMC). This added thickness gives RMC superior strength and impact resistance. IMC, while still very durable, is lighter and has a slightly larger internal diameter, which can sometimes make wire pulling easier. The choice often comes down to the specific demands of the installation. For the most demanding environments, and where maximum physical protection is required, RMC is often preferred because of its heavier wall; however, IMC is also explicitly permitted by the NEC for many installations and may be specified where weight or ease of handling is a factor.

Pre-Installation Planning: Tools, Materials, and Protection

A successful rigid metal conduit installation begins with proper preparation. Gathering the correct tools and materials beforehand prevents delays and ensures a code-compliant job. Pay special attention to the environment, as supplemental conduit corrosion protection may be necessary beyond the standard galvanization. For instance, wiring systems in corrosive environments requires specific materials and coatings.

• Essential Tools: Pipe cutter or band saw, level, tape measure, and a power or manual pipe threader for executing proper conduit threading techniques. For larger sizes, a hydraulic conduit bender is indispensable for creating smooth, accurate bends.
• Conduit & Fittings: Sticks of RMC conduit, couplings, factory elbows, and various conduit body types (e.g., LB, LL, LR, T, C) for navigating turns and providing access points.
• Enclosures and Supports: Straps, hangers, and enclosures like electrical pull boxes and junction boxes. For larger conductor management, you may also integrate the system with wireways or an electrical gutter.
• Specialty Fittings: For specific applications, you’ll need items like sealing fittings and explosion proof fittings for classified hazardous locations; always use fittings listed for the location and the enclosure.

The Step-by-Step Guide on How to Install RMC Conduit

Executing a flawless RMC installation requires precision at every stage. Follow this professional process to ensure your work is safe, durable, and compliant.

1. Measure and Cut: Measure the required length of conduit between termination points or fittings. Use a pipe cutter, portable band saw, or hacksaw to make a straight, square cut. Accuracy here minimizes waste and helps ensure tight-fitting joints that can be properly reamed and threaded per good practice and the guidance found in NEC Article 344.
2. Perform Conduit Reaming and Deburring: This is a non-negotiable step. After cutting, the inside edge of the conduit will be sharp. Use a reaming tool or a deburring head to smooth this edge completely. Failing to perform proper conduit reaming and deburring can strip wire insulation during pulling, creating a serious shock or fire hazard.
3. Master Conduit Threading Techniques: Using a manual or power threader, cut NPT (National Pipe Taper) threads onto the end of the conduit (or use the manufacturer’s recommended metric thread where equipment or fittings require metric threads). Apply cutting oil to ensure clean, sharp threads and to prolong the life of your dies. The threads must be clean and well-formed to ensure a solid mechanical connection and to help maintain a continuous conductive path where the raceway is used as an equipment grounding path.
4. Execute Bending Rigid Conduit: For field bends, use a mechanical or hydraulic conduit bender. Follow the bender’s instructions carefully to avoid kinking or flattening the conduit; improper bending that damages the conduit can violate the installation requirements in Article 344. For complex layouts or back-to-back 90s, meticulous layout and math are essential.
5. Assemble and Secure Components: Thread the conduit into couplings, fittings, and hubs until it is wrench-tight or assembled per the fitting manufacturer’s instructions. For enclosure entries, a proper threaded hub installation or a listed hub appropriate for the application is key to maintaining the system’s integrity, especially for wet locations. Secure the conduit run according to conduit support requirements outlined in NEC Article 344 — for example, securing within 900 mm (3 ft) of outlets and supporting at typical intervals around 3 m (10 ft) unless a specific size or condition requires closer spacing.

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Advanced Considerations for RMC Systems

Beyond the basic installation, professional electricians must understand the critical roles RMC plays in specialized applications. These considerations separate a standard installation from an expert one.

Grounding and Bonding Conduit

One of the primary advantages of an RMC system is that the raceway can serve as an equipment grounding path where permitted (see NEC Article 250). This depends on a continuous conductive path using listed fittings and proper assembly; connections should be properly made and verified rather than relying only on loose or unlisted hardware. Proper grounding and bonding conduit ensures a continuous, low-impedance path for fault current to travel back to the source, allowing the overcurrent protection device to operate quickly.

Hazardous Location Wiring Methods and Physical Protection

In classified areas (e.g., Class I, Division 1), RMC is among the approved hazardous location wiring methods when installed with listed explosionproof fittings and sealing where required. When used with listed fittings and sealing compounds, threaded metal raceways can contain and limit the effects of internal arcing and help prevent ignition of the surrounding atmosphere. IMC and other methods are also listed for certain hazardous installations, so always follow the listing and the authority having jurisdiction’s direction.

Service Entrance Conduit

Due to its strength and durability, RMC is frequently specified as the service entrance conduit. It provides high protection for service-entrance conductors as they run from the weatherhead down to the meter base and into the main service panel, and it is a permitted wiring method for service-entrance conductors when installed per Article 230 requirements.

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Frequently Asked Questions

What are the main steps on how to install RMC conduit according to NEC Article 344?

The primary steps are: planning the run, accurately measuring and cutting the conduit, performing thorough conduit reaming and deburring to protect wires, using proper conduit threading techniques for strong connections, precisely bending rigid conduit as needed, and securing the system according to NEC conduit support requirements.

When are explosion proof fittings required for a rigid metal conduit installation?

Explosionproof fittings are required when the conduit and associated equipment are used in classified hazardous locations where such fittings are specified by the NEC and the equipment listing. These fittings are designed and listed to contain an internal explosion and prevent it from igniting flammable gases, vapors, or dust in the surrounding environment.

What are the primary differences in the IMC vs RMC conduit debate?

The main difference is wall thickness and weight. RMC has a thicker wall, making it heavier but also providing superior physical protection. IMC is lighter and may be easier to handle and pull wire through in many commercial applications. The choice depends on the level of physical protection required by the NEC and the specific job site conditions.

Why is grounding and bonding conduit so critical with RMC?

Properly grounding and bonding conduit is critical because the metal raceway can serve as the equipment grounding path where permitted by NEC Article 250. This relies on a continuous conductive path using listed fittings and correct assembly; verify continuity and bonding during installation to ensure the path will safely conduct fault current back to the supply and allow overcurrent protective devices to operate.