Rigid Electrical Conduit 101: What It Is and Why It Matters

A rigid electrical conduit is a tube-like structure used to encase and protect electrical wiring. As the name suggests, it is rigid, meaning that it is non-flexible and provides a solid, protective barrier for cables.

It is typically used in environments where wiring needs maximum protection from external elements or where electrical installations must comply with stringent safety regulations.
Rigid electrical conduit is available in a variety of forms, each designed to serve specific needs depending on the material and application.The primary materials used for rigid electrical conduits include PVC (Polyvinyl Chloride), galvanized steel, aluminum, and RTRC (Reinforced Thermosetting Resin Conduit), among others.Each material brings unique advantages, making rigid conduit versatile across a range of environments and project requirements.By the end of this post, you will have a thorough understanding of what rigid electrical conduit is, why it is an essential component in modern electrical systems, and how to incorporate it into your next project to maximize safety, efficiency, and compliance.

Rigid conduit can be roughly divided into metal, plastic, and glass fiber, depending on the material. Each type of conduit serves distinct needs depending on the installation environment and specific project requirements.

Metal Rigid Conduit includes types like Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), and Electrical Metallic Tubing (EMT), known for their strength and durability, making them suitable for industrial and outdoor use.Plastic Rigid Conduit, such as Rigid Polyvinyl Chloride (PVC), is lightweight, corrosion-resistant, and commonly used in environments where moisture protection is essential, like underground installations.

Additionally, RTRC conduit, made from fiberglass, offers excellent electrical insulation, thermal resistance, and corrosion protection, making it an ideal choice for applications requiring non-conductive and high-strength materials.

In the following article, we will present the details of rigid conduit made from different materials.

Rigid Metal Conduit (RMC)

In accordance with NEC Article 344, Rigid Metal Conduit (RMC) is a threaded raceway with a circular cross-section, designed to protect and route conductors and cables. It can also function as an equipment grounding conductor when used with the proper couplings and fittings.

RMC is available in the following materials:

• Steel with protective coatings
• Aluminum
• Red brass
• Stainless steel

RMC comes in different types depending on the material used in its construction, each with a common name.

Electrical Rigid Metal Conduit – Steel (ERMC-S)

According to UL 6 Standard for Safety Electrical Rigid Metal Conduit – Steel.

ERMC-S is a threadable steel raceway of circular cross-section designed for the physical protection and routing of wire conductors and use as an equipment grounding conductor when installed utilizing appropriate fittings.

RSC is provided with a zinc, zinc-based, nonmetallic, or other alternate corrosion-resistant exterior coating and an organic or zinc interior coating.

NEC Article 344 specifies that RMCs made of steel must have a protective coating to enhance their resistance to moisture, corrosion, and impact.

Specifications for Rigid Metal Conduit (RMC-S)

Material and Structure

Each tube used for Rigid Steel Conduit (RSC) shall be made of steel, ensuring that it is straight and features a circular cross-section.

These specifications are crucial for ease in cutting and threading, as per the dimensions outlined in the following Table.

Metric Designator	Outside Diameter (mm)	Trade Size	Outside Diameter, a (in)
12b	17.15	3/8b	0.675
16	21.34	1/2	0.840
21	26.67	3/4	1.050
27	33.40	1	1.315
35	42.16	1-1/4	1.660
41	48.26	1-1/2	1.900
53	60.33	2	2.375
63	73.03	2-1/2	2.875
78	88.90	3	3.500
91	101.60	3-1/2	4.000
103	114.30	4	4.500
129	141.30	5	5.563
155	168.28	6	6.625

a Tolerances: Trade Size 12–41 (3/8–1-1/2) ± 0.38 mm (±0.015 in). Trade Size 53–155 (2–6) ± 1%.
b In the United States, 12 (3/8) trade size is permitted for special applications. In Canada, 12 (3/8) trade size is not permitted according to the Canadian Electrical Code, Part I.

The wall thickness must remain uniform throughout the entire length of the tube to maintain consistency in protection and support. Additionally, all seams in the tube shall be thoroughly welded to ensure structural integrity and durability.

Welded Seams

The welding process for RMC tubes must meet strict criteria to ensure safety and functionality.

Welded seams should not have metal trimmings, sharp edges, or projections that could interfere with the internal wiring or the installation process.

A slight bead along the interior of the seam is permissible, as long as it is smooth and does not exceed 0.38 mm (0.015 in) in height for trade sizes 12 to 53 (3/8 inch to 2 inches) or 0.51 mm (0.020 in) for trade sizes 63 to 155 (2 ½ inches to 6 inches).

Standard Length and Weight Requirements

The standard length of straight zinc-coated conduit or bare threaded tubes to be coated with an alternate corrosion-resistant material, including one coupling, must follow the specifications detailed Table in the followinggs.

These tables outline the dimensions and weights for conduit that complies with the given standards.

Metric Designator	Length of Straight Conduita (mm)	Min. Acceptable Weight of 10 Lengths of Conduit with Ten Couplings, (kg) Finished Zinc Coated Conduitb	Min. Acceptable Weight of 10 Lengths of Conduit with Ten Couplings, (kg) Bare Threaded Tubec	Trade Size	Length of Straight Conduit Feet and Inchesa ±1/4	Min. Acceptable Weight of 10 Lengths of Conduit with Ten Couplings, (lbs) Finished Zinc Coated Conduitb	Min. Acceptable Weight of 10 Lengths of Conduit with Ten Couplings, (lbs) Bare Threaded Tubec
12d	3035	23.4	22.6	3/8	9′–11 1/2″	51.5	48.6
16	3030	35.8	34.4	1/2	9′–11″	78.9	75.8
21	3030	47.6	45.5	3/4	9′–11″	104.9	100.3
27	3030	69.4	65.8	1	9′–11″	153.0	145.1
35	3025	91.2	87.8	1-1/4	9′–11″	201.0	193.5
41	3025	112.9	109.4	1-1/2	9′–11″	249.0	241.2
53	3035	150.4	144.3	2	9′–11 1/2″	331.6	318.1
63	3010	209.6	203.4	2-1/2	9′–10 1/4″	462.0	448.4
78	3010	239.0	233.4	3	9′–10 1/4″	527.0	514.8
91	3010	274.1	268.4	3-1/2	9′–10 1/4″	604.4	591.5
103	2995	312.0	305.3	4	9′–10″	687.6	672.9
129	2995	591.7	578.6	5	9′–10″	1304.9	1275.6
155	2995	797.1	781.4	6	9′–10″	1757.0	1722.7

a The lengths indicated are designed to produce a 3.05 m (10 ft) length of conduit when a straight-tapped conduit coupling is attached.
b This conduit is protected with a zinc or zinc-based coating consisting primarily of zinc.
c This conduit is intended to be protected with an alternate corrosion-resistant coating.
d In the United States, 12 (3/8) trade size is permitted for special applications. In Canada, 12 (3/8) trade size is not permitted according to the Canadian Electrical Code, Part I.

Test Requirements

Tubing Testing of Rigid Steel Conduit

The tube testing process involves bending a sample of the smallest available trade size into a quarter circle around a mandrel, first at room temperature and then after conditioning it at 0°C (32°F) for 60 minutes.

The tube must not crack or break its weld. If the tube has a nonmetallic coating and is rated for temperatures below 0°C, the test is performed at that lower temperature.

Test the flexibility and durability of rigid steel conduit when bent under both normal and cold conditions.

Coatings	Tests	Clause #
Zinc	Bend Test Cold Bend Zinc Coating Test	6.2.1.1 6.2.1.3 6.2.2
Alternate Corrosion-Resistant	Bend Test Cold Bend Ultraviolet Light and Water Salt Spray (Fog) Moist CO₂–SO₂–Air Tensile Adhesion Flame Propagation	6.2.1.1 6.2.1.3 6.2.4.3 6.2.4.5 6.2.4.6 6.2.4.8 6.2.4.9 6.2.4.11
Alternate Corrosion-Resistant Nonmetallic (in addition to the above)	Assembly, Bending, Resistance, Pull, and Fault Current Electrical Continuity Identification of Compounds Cold Impact	5.3.3.2 5.3.5.2 6.2.1.5 6.2.1.0
Organic	Bend Test Cold Bend Identification of Compounds Elasticity Warm Humid Air Test	6.2.1.1 6.2.1.3 6.2.1.5 6.2.3.5 6.2.3.2
Supplementary Coatings	Detrimental Effects to Primary Coating Fit of Couplings Electrical Continuity Flame Propagation	5.3.5.2 5.3.5.2 5.3.5.2 6.2.4.11
Surface Treatment	N/A if less than 0.038 mm (0.00015 in) thickness	5.3.6.1

The goal is to ensure the tube can withstand bending without cracking or breaking, especially at weld points.

The test also ensures the tube’s protective coatings remain intact at varying temperatures.

*While these specifications serve as a guideline for standard conduit production, additional guidelines are provided in Annex for further and detailed reference purposes. Please consult the relevant documents for comprehensive requirements and specifications.

Coating Testing of Rigid Steel Conduit

The table in the following outlines different tests for various types of coatings applied to tubes, including zinc, alternate corrosion-resistant, nonmetallic, organic, and supplementary coatings.

These tests assess the coating’s performance under different conditions such as bending, exposure to UV light, salt spray, cold temperatures, and electrical continuity.

The purpose of these tests is to ensure that the coatings provide adequate protection against environmental factors like corrosion, impact, and wear, maintaining the tube’s structural integrity and performance across different applications and environments.

Other Types of Rigid Metal Conduit

Electrical Rigid Metal Conduit – Stainless Steel (ERMC-SS)

A threadable stainless steel raceway of circular cross-section designed for the physical protection and routing of wire conductors and use as an equipment grounding conductor when installed utilizing appropriate fittings.

Electrical Rigid Metal Conduit – Red Brass (ERMC-RB)

A threadable red brass raceway of circular cross-section designed for the physical protection and routing of wire conductors and use as an equipment grounding conductor when installed utilizing appropriate fittings.

Electrical Rigid Metal Conduit – Aluminum (ERMC-A)

A threadable aluminum raceway of circular cross-section designed for the physical protection and routing of wire conductors and cables and for use as an equipment grounding conductor.

Electrical Intermediate Metal Conduit (EIMC)

Electrical Intermediate Metal Conduit (EIMC) is a threadable steel raceway with a circular cross-section, designed for the physical protection and routing of conductors and cables.  It can also serve as an equipment grounding conductor.

Trade Size	Outside Diameter (in.) Max	Outside Diameter (in.) Min	Wall Thickness (in.) Max	Wall Thickness (in.) Min	Nominal Inside Diameter (in.)	Length w/o Coupling (ft & in.)
1/2	0.820	0.810	0.085	0.070	0.659	9’11-1/4″
3/4	1.034	1.024	0.090	0.075	0.863	9’11-1/4″
1	1.295	1.285	0.100	0.085	1.063	9’11”
1-1/4	1.645	1.630	0.105	0.085	1.448	9’11”
1-1/2	1.890	1.875	0.115	0.090	1.683	9’11”
2	2.367	2.352	0.115	0.095	2.150	9’11”
2-1/2	2.867	2.847	0.160	0.140	2.575	9’10-1/2″
3	3.486	3.466	0.160	0.140	3.176	9’10-1/2″
3-1/2	3.981	3.961	0.160	0.140	4.161	9’10-1/4″
4	4.476	4.456	0.160	0.140	4.166	9’10-1/4″

According to ANSI C80.6-2005, the exterior of EIMC must be uniformly coated with metallic zinc or an alternate corrosion-resistant coating. The interior must have a smooth coating of zinc or an organic material, with minor irregularities allowed.

Materials:
• Steel with protective coatings
• Aluminum

Testing: EIMC undergoes bending tests to ensure ductility and coating integrity. Smaller sizes are bent 180°, larger sizes 90°, checking for cracks or peeling. Zinc thickness is verified via magnetic and copper sulfate tests. Organic coatings are baked and bent to check resistance.

Purpose of Testing: These tests confirm the conduit’s mechanical performance, safety, and long-term corrosion resistance in electrical installations.

Electrical Metallic Tubing (EMT)

Qualification Tests for Reinforced Thermosetting Resin Conduit (RTRC)

How to Install Rigid Metal Conduit: A Step-by-Step Guide

Metal conduit systems, such as steel rigid metal conduit (RMC), intermediate metal conduit (IMC), and electrical metallic tubing (EMT), provide essential protection to electrical wiring. These systems safeguard wires from damage, ensure proper grounding, and help maintain compliance with the National Electrical Code (NEC). Using pre-threaded and corrosion-coated conduit can simplify installation and improve durability.

Preparation: Tools and Planning

Before starting, gather the following tools and materials:

• Cutting tools: Hacksaw or roll cutter (if cutting is required).
• Reamer: To remove burrs inside the conduit after cutting.
• Conduit bender: For making precise bends.
• Wrenches: Appropriately sized.
• Thread-sealing compound or corrosion-resistant paint: To protect threads if necessary.

Also confirm you have all necessary fittings, couplings, and connectors to ensure proper grounding.

Cutting and Threading (If Needed)

• Measure and Cut: Measure required length and cut cleanly with a saw.

• Ream: Remove burrs inside the conduit to avoid wire damage.

• Threading: Use a standard ¾-inch per foot (NPT) die for threading if needed. Threads should be smooth and clean.

For pre-threaded conduit, skip threading but protect exposed or damaged threads.

Connecting and Tightening the Conduit

• Hand-Tighten and Wrench Finish: Start hand-tightening, then wrench-tighten typically one full turn beyond hand-tight.

• Avoid Over-Tightening: Excessive force can damage threads and coating. Do not use wrench extensions.

• For threadless fittings, push conduit fully into fitting and secure with appropriate torque.

Bending the Conduit

• Hand Bending: Small sizes (½ to 1 inch) can be bent with a hand bender; larger sizes require mechanical or power benders.

• Precision: Mark bends; avoid exceeding 90° between pulling points.

• Avoid Kinks: Prevent flattening or kinking, which reduces space and complicates wire pulling.

• For pre-threaded conduit, avoid damaging threads during bending.

Supporting and Securing the Conduit

• Use straps, hangers, or clamps to secure conduits to walls, ceilings, or structural members.

• For vertical runs, secure conduit at the top end to prevent sagging.

• For conduits transitioning from concrete to soil or underground, apply approved coatings, wraps, or PVC-coated conduit for extra protection.

Corrosion Protection in Severe Environments

• Inspect factory-applied coatings for damage during installation.

• Apply corrosion-resistant compounds, zinc-rich paint, or corrosion-resistant tape as needed.

• Protect field-cut threads with corrosion-resistant, electrically conductive coatings.

Final Testing and Verification

• Perform continuity testing to confirm electrical continuity and grounding.

• Inspect all conduit connections for tightness and secure supports.

• Verify protective coatings remain intact and additional protections are applied as necessary.

How to Install PVC Rigid Conduit: A Step-by-Step Guide

PVC (polyvinyl chloride) rigid conduit is a versatile, lightweight, and non-metallic solution for protecting electrical wiring in various environments. It’s commonly used in outdoor, wet, or underground installations due to its resistance to moisture and corrosion. Installing PVC conduit requires specific techniques that differ from installing metal conduit, particularly in how it is cut, joined, and supported.

Tools and Materials Needed for Installation

Before you begin, gather the necessary tools and materials for a successful PVC conduit installation:

PVC Conduit: The appropriate diameter and length for your project.
PVC Fittings: Couplings, elbows, junction boxes, and other components.
PVC Cement and Primer: To secure joints and fittings.
Conduit Cutter or Hacksaw: To cut the conduit to the required length.
Deburring Tool: To smooth the cut edges of the conduit.
Tape Measure: For accurate measurements.
Level: To ensure proper alignment.
Pull String or Fish Tape: To pull wires through the conduit after installation.

Planning the Layout and Measuring the Run

Before starting the installation, carefully plan the route for your PVC conduit. This includes measuring the distance between points where the conduit will run and mapping out where bends, fittings, and junctions will be needed.

Measure and Mark: Use a tape measure to determine the length of PVC conduit required for each section and mark where cuts will be made.

Account for Expansion and Contraction: PVC conduit expands and contracts with temperature changes, so you’ll need to leave some room for movement or install expansion fittings in long runs.

Cutting and Deburring the PVC Conduit

Cutting PVC conduit is much easier than cutting metal conduit, but it’s still important to make clean, precise cuts to ensure a smooth installation.

Cut the Conduit: Use a PVC conduit cutter or a fine-toothed hacksaw to cut the conduit to the measured lengths. Make sure the cuts are straight and clean.

Deburr the Edges: After cutting, use a deburring tool or a utility knife to remove any rough edges or burrs from inside and outside the conduit. This step is crucial to prevent damaging the wires when they’re pulled through the conduit.

Joining PVC Conduit with Solvent-Welding

Unlike metal conduit, where threads or set-screw fittings are used, PVC conduit sections are joined by a process called solvent-welding. This involves using a primer and PVC cement to bond the conduit and fittings together.

Apply Primer: First, clean the ends of the conduit and the inside of the fittings using a PVC primer. The primer softens the material and prepares it for the bonding process.

Apply PVC Cement: Immediately after applying the primer, coat the same areas with PVC cement. Be sure to work quickly, as the cement dries fast.

Join the Conduit and Fittings: Push the conduit into the fitting, twisting slightly to ensure the cement spreads evenly. Hold the pieces together for a few seconds to ensure a strong bond.

Wipe Off Excess Cement: Remove any excess cement that squeezes out during the connection process. Allow the joint to set according to the manufacturer’s instructions before handling it further.

This solvent-welding process creates a watertight seal, making PVC ideal for outdoor and underground installations where moisture resistance is critical.

Bending PVC Conduit

Bending PVC conduit is different from bending metal conduit. PVC can be bent using heat to create smooth, custom bends without the need for prefabricated elbows in some situations.

Heat the PVC Conduit: Use a heat gun or PVC bending heater to warm the section of the conduit where the bend is needed. Be sure to apply heat evenly to avoid deforming the conduit.

Make the Bend: Once the conduit is pliable, bend it slowly to the desired angle. Hold it in place until the conduit cools and retains the shape.

Use Pre-Made Elbows: For most installations, it’s easier to use factory-made 90-degree or 45-degree PVC elbows, which are glued in place using the same solvent-welding process.

Supporting the PVC Conduit

Since PVC is more flexible and lightweight than metal conduit, it requires proper support to prevent sagging or movement over time.

Install Conduit Straps or Clamps: Support the PVC conduit at regular intervals by securing it with conduit straps or clamps. Follow NEC guidelines, which recommend supporting PVC every 3 to 6 feet, depending on the diameter of the conduit.

Allow for Expansion: PVC conduit expands and contracts with temperature changes. In longer runs, install expansion fittings to allow movement without stressing the joints. Expansion fittings are crucial for outdoor or sun-exposed installations where temperature fluctuations are significant.

Pulling Wires through PVC Conduit

After the conduit is installed and the cement joints have cured, you can pull wires through the conduit.

Use a Fish Tape or Pull String: Feed the fish tape or pull string through the conduit run, then attach the wires securely to the tape.

Pull the Wires: Slowly pull the wires through the conduit, ensuring that they don’t snag or get damaged on any rough edges.

Lubricate If Necessary: If the conduit run is long or has several bends, use a wire-pulling lubricant to reduce friction and make the wire-pulling process easier.

Testing and Final Inspection

Once the wires are pulled and the system is set up, perform a final inspection to ensure everything is installed correctly and securely.

Check Connections: Ensure all solvent-welded joints are solid and that no fittings have loosened.

Verify Supports: Confirm that all conduit straps and clamps are properly spaced and secure.

How to Install RTRC Conduit: A Step-by-Step Guide

Tools and Materials Needed for Installation

For a successful RTRC conduit installation, gather the following tools and materials:

• RTRC Conduit: Appropriate diameter and lengths of conduit.
• RTRC Fittings: Couplings, elbows, and other necessary components.
• Two-Part Epoxy or Adhesive: To bond conduit sections and fittings.
• Hacksaw or Fine-Toothed Saw: For cutting the conduit to size.
• Deburring Tool or Sandpaper: To smooth cut edges.
• Measuring Tape and Level: For precise measurements and alignment.
• Pull String or Fish Tape: To pull wires through the conduit after installation.
• Heat Gun: For heat-shrink components if needed.

Planning the Layout and Measuring the Run

As with any conduit system, start by planning the route and layout for the RTRC installation. Identify the points where conduit runs will change direction, where fittings will be needed, and where access points or junction boxes should be placed.

Measure and Mark: Use a tape measure to accurately determine the lengths of conduit required and mark where cuts will need to be made.

Cutting and Deburring RTRC Conduit

Cutting RTRC conduit is similar to cutting PVC, but the material’s composition requires careful handling to prevent fiber damage.

Cut the Conduit: Use a hacksaw, reciprocating saw, or any fine-toothed saw to cut the conduit to the desired length. Make sure the cut is straight to allow for proper joining.
Deburr the Edges: After cutting, smooth the inside and outside edges using a deburring tool or sandpaper. This prevents damage to wire insulation.
Dust Control: When cutting RTRC, use PPE such as gloves, eye protection, and a dust mask or respirator to manage fiberglass dust.

Joining RTRC Conduit with Adhesive Bonding

RTRC conduit is joined using adhesives or a two-part epoxy designed for fiberglass conduit systems.

Prepare the Surfaces: Clean conduit ends and fitting interiors to remove dust, dirt, and oil.
Apply the Adhesive: Use the recommended epoxy. Apply generously to both joining surfaces.
Join and Set: Insert and twist the conduit into the fitting. Hold briefly until set begins.
Curing Time: Allow full curing as per manufacturer guidelines before applying load or stress.

Supporting RTRC Conduit

RTRC conduit needs adequate support, especially in horizontal applications:

• Use approved straps, hangers, or clamps every 6–10 feet per NEC requirements.
• Expansion Joints: Include expansion fittings in long runs or areas with temperature swings.

Bending RTRC Conduit

Bending RTRC conduit is typically not done on site:

• Use factory-made elbows and bends (e.g., 90°, 45°), joined with adhesive.
• No Heat Bending: Heating damages RTRC’s structural integrity.

Pulling Wires Through RTRC Conduit

Once adhesive is cured, proceed to wire installation:

• Use fish tape or pull string to guide wires through conduit.
• Apply lubricant on long or complex runs to ease pulling.
• Ensure NEC-compliant grounding and bonding, as RTRC is non-conductive.

Testing and Final Inspection

Before energizing the system:

• Inspect all adhesive joints to confirm secure bonding.
• Verify that all supports are in place and at correct intervals.

Ctube is a premier manufacturer of high-quality PVC conduit solutions, dedicated to delivering reliable and durable products for electrical installations.

Based in China, we specialize in producing a wide range of conduits designed to meet the diverse needs of various industries, all while ensuring compliance with international standards.

Our PVC rigid conduit adheres to rigorous certifications such as UL 651, AS/NZS 2053, and CSA, guaranteeing exceptional performance, durability, and safety across different regions. 

Thank you for reading!  We hope this post was helpful to your project. Wishing you success in all your work — and feel free to reach out to us if you have any project needs or inquiries.

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