Conduit 101

Foundational Understanding

1. What types of conduit are commonly used?

Conduit types vary based on environment, durability, and code requirements. Choosing the right type ensures safety, longevity, and compliance. Each has specific strengths for indoor, outdoor, or specialty use.

• EMT: Lightweight and easy to bend; ideal for commercial interiors.
• RMC: Thick-walled and corrosion-resistant; used outdoors and underground.
• IMC: Lighter than RMC but still suitable for exposed areas.
• FMC: Used for equipment terminations and vibration zones.
• ENT: Flexible plastic; used in low-voltage or plenum-rated spaces.
• PVC: Non-metallic and moisture-resistant; common in underground or wet locations.

2. How is conduit different from other raceways?

The terms are related but not interchangeable. Conduit is a specific type of raceway, typically a tubular enclosure for electrical conductors. Raceway is a broader category that includes multiple wiring methods.

• Conduit: Tubular, enclosed, and often metallic or plastic.
• Raceway: Includes conduit, cable trays, wireways, and surface raceways.
• NEC Article 100: Defines both terms clearly.
• All conduit is raceway: But not all raceway is conduit.

3. What NEC articles apply to conduit installation?

The National Electrical Code (NEC) defines how conduit must be installed, supported, and grounded. Articles vary by conduit type and application. Knowing the right references ensures compliant and inspectable work.

• NEC 300.11: General support and securement.
• NEC 358.30: EMT-specific support spacing.
• NEC 250: Grounding and bonding requirements.
• NEC 300.3(C): Separation of power and low-voltage systems.
• NEC 300.5: Minimum burial depths for underground conduit.

Application Zones and Requirements

4. Where is conduit installation required?

Conduit is required where wiring needs physical protection or environmental shielding. Common zones include exposed areas, outdoors, underground, hazardous locations, and plenum spaces. Service entrances and mechanical zones also require conduit.

• Exposed wiring: In garages, basements, utility rooms, and commercial spaces.
• Outdoor installations: Use RMC, IMC, or PVC conduit for weatherproof protection.
• Underground runs: Protects conductors from soil, moisture, and mechanical damage.
• Hazardous locations: Classified areas require sealed conduit systems per NEC Article 501.
• Commercial and industrial buildings: EMT or RMC is typically required for branch circuits and feeders.
• Plenum spaces: ENT or metal conduit may be required to meet fire and smoke ratings.
• Service entrances and meter enclosures: Protects conductors entering buildings or equipment.
• High-traffic or mechanical zones: Shields wiring from vibration, abrasion, and impact.
• Jurisdictional requirements: Some areas require all cable—including low-voltage and MC—to be installed in conduit.

5. What does conduit connect to?

Conduit connects electrical systems to enclosures, devices, and other raceways. Each connection must be mechanically secure and electrically continuous. Fittings vary by conduit type and environment.

• Junction and device boxes: For splices, terminations, and transitions.
• Panelboards and switchgear: For feeders and branch circuits.
• Equipment terminations: Lighting, HVAC, motors, receptacles.
• Cable trays and wireways: For system integration or transitions.
• Sleeves and stubs: For wall, floor, or underground penetrations.

Components and Installation

6. What components are used with conduit?

Conduit systems rely on a range of fittings and accessories to ensure secure, grounded, and code-compliant installations. Each component serves a specific function—mechanical, electrical, or environmental. Selection depends on conduit type and location.

• Connectors and couplings: EMT set-screw, compression, or threaded types.
• Bushings and locknuts: Protect conductors and secure conduit to boxes.
• Straps and hangers: Maintain support spacing and alignment.
• Bonding jumpers: Ensure grounding continuity across disjointed runs.
• Expansion fittings: Allow for thermal movement in long runs.
• Sealing fittings: Required in hazardous or classified locations.

7. How is conduit supported?

Conduit must be mechanically secured to prevent sagging, vibration, or damage. Support methods depend on conduit type, size, and routing environment. NEC defines maximum spacing intervals for each type.

• Strut and trapeze racks: Used for overhead and multi-run support.
• Individual hangers or straps: Common for wall or ceiling-mounted conduit.
• Spacing: EMT typically requires support every 10 feet or within 3 feet of a box.
• Vertical runs: May require intermediate supports or riser clamps.

8. Can conduit be buried?

Yes—conduit can be buried to protect wiring from physical damage, moisture, and environmental exposure. The type of conduit and burial depth depend on voltage, location, and protection method. NEC Article 300.5 governs burial requirements.

• PVC and RMC: Most common for underground use.
• Minimum depth: 18" for residential branch circuits; varies by system.
• Concrete encasement: Required in high-traffic or shallow-depth zones.
• Expansion joints: May be needed for long runs or temperature swings.

Conductor Routing and Fill

9. What can be pulled through conduit?

Conduit is designed to route and protect electrical conductors. What you pull depends on system type, voltage, and code requirements. NEC fill limits and separation rules must always be followed.

• Power conductors: THHN, XHHW, or other insulated copper/aluminum wires.
• Low-voltage cabling: CAT6, coaxial, control, or fire alarm wiring.
• MC cable: May be sleeved but not typically pulled through full-length conduit.
• Fiber optic cable: Allowed in ENT or dedicated raceways; follow bend radius and separation protocols.
• Grounding conductors: Bare or insulated, sized per NEC Article 250.
• Pull cords or fish tape: Used during installation only.

10. How do I calculate conduit fill?

Conduit fill limits how many conductors can be installed without overheating or violating code. It’s based on conductor size, insulation type, and conduit dimensions. NEC Chapter 9 Table 1 and Annex C provide the official values.

• Formula: Total conductor area ÷ conduit area ≤ allowed fill %.
• Fill limits: 53% for one conductor, 31% for two, 40% for three or more.
• Annex C: Lists pre-calculated conductor counts by type and size.
• Include all conductors: Ground wires count toward fill.
• Don’t forget derating: Adjust for ambient temperature and conductor count.

Transitions and Reuse

11. What are the rules for conduit transitions?

Transitions between conduit types must maintain mechanical integrity and electrical continuity. NEC requires listed fittings when switching between dissimilar materials. Improvised transitions are not permitted.

• Use transition couplings: Threaded, compression, or adapter-style.
• Bonding continuity: Must be preserved across metallic transitions.
• Expansion concerns: PVC-to-metal transitions may require expansion fittings.
• Listed fittings only: Improvised or field-fabricated transitions are not permitted.

12. Can conduit be reused?

Conduit can be reused under specific conditions, but it must meet current code and be free of damage. Inspect for corrosion, deformation, and thread integrity before reuse.

• Metal conduit: May be reused if undamaged and properly cleaned.
• PVC conduit: Often not reusable due to glue joints and UV degradation.
• Fittings and boxes: Must be re-rated or replaced if damaged.
• Labeling and layout: Reused conduit must match the new system’s specs.

Bending and Layout

13. What should I know about conduit bending?

Conduit bending is essential for clean layouts and proper wire pulling. Bends must be accurate, smooth, and within code-defined limits. Improper bends can damage conductors or complicate installation.

• Hand benders: For EMT up to 1¼".
• Mechanical/hydraulic benders: For larger conduit sizes.
• Common bends: 90° stub-ups, offsets, saddles, back-to-back 90s.
• Bend radius: Must meet NEC Chapter 9 Table 2.
• Account for gain and shrink: Especially in tight layouts.

14. Is parallel conduit installation required or recommended?

While not always required by code, parallel conduit runs are a best practice in many installations. They improve layout clarity, aesthetics, and troubleshooting. AHJs often expect parallelism in professional environments.

• Electrical rooms and data centers: Require clean, aligned conduit banks.
• Spacers and jigs: Help maintain consistent spacing.
• Prefab racks: Speed up install and ensure uniformity.
• Laser alignment: Useful for long runs or high-visibility zones.

Hazards and Grounding

15. What hazards should be avoided when routing conduit?

Improper conduit routing can lead to corrosion, mechanical damage, or code violations. Mechanical rooms, HVAC zones, and wet areas require special attention. Routing must also consider fire ratings and access.

• Avoid chilled water lines and condensate drains: Prevents corrosion and condensation.
• Keep clear of HVAC ducts: Avoids airflow obstruction and temperature extremes.
• Use plenum-rated materials: Required in air-handling spaces.
• Maintain working clearances: Especially near panels and disconnects.

16. How do you ensure conduit is grounded?

Grounding ensures safety by providing a low-impedance path for fault current. Metallic conduit must be bonded at all connections to maintain continuity. NEC Article 250 outlines the requirements.

• Bonding bushings: Used where concentric/eccentric knockouts are present.
• Grounding locknuts: Provide mechanical and electrical continuity.
• Jumpers: Required across non-continuous metallic paths.
• Testing: Use continuity testers or megohmmeters to verify bonding.

Bend Limits and Firestop

17. What are conduit bend limitations?

NEC limits the number and angle of bends to ensure pullability and conductor protection. Excessive bends increase friction and risk conductor damage. Planning bends early helps avoid layout issues.

• Maximum bends: No more than 360° total between pull points.
• Minimum radius: Defined in NEC Chapter 9 Table 2.
• Segmented bends: Use offsets or saddles to avoid sharp angles.
• Pull boxes: Required when bend limits are exceeded.

18. What are conduit firestop requirements?

Conduit passing through fire-rated assemblies must be sealed to prevent smoke and flame spread. NEC and building codes require UL-listed firestop systems. Coordination with other trades is essential.

• Sleeves and collars: Used for wall and floor penetrations.
• Intumescent sealants: Expand under heat to seal gaps.
• Inspection tags: Firestop systems must be labeled and documented.
• Firestop kits: Must match wall rating and conduit type.

Inspection Readiness

19. What do inspectors look for in conduit installations?

Conduit installations are inspected for mechanical integrity, grounding, spacing, and code compliance. AHJs may require visual, continuity, and torque checks. Preparing for inspection avoids costly delays.

• Support spacing: Verified against NEC requirements.
• Bonding and grounding: Checked for continuity and secure terminations.
• Box fill and conduit fill: Must match calculated limits.
• Labeling and routing: Must match approved plans and system layout.