Conduit and Raceway Guide: Types, Sizing, and Installation Requirements

Updated April 2026 · By the WiringCalcs Team

Electrical conduit protects wiring from physical damage, moisture, chemicals, and rodents while providing a pathway for future wire additions and replacements. Choosing the right conduit type and size for each application ensures code compliance, installation efficiency, and long-term system flexibility. This guide covers the most common conduit types, NEC fill requirements, bending basics, and when to use each type for residential and commercial applications.

Common Conduit Types

EMT (Electrical Metallic Tubing) is the most widely used conduit in commercial construction. It is lightweight, inexpensive ($0.50-2.00 per foot), and easy to bend with a hand bender. EMT uses compression or set-screw fittings — no threading required. It provides mechanical protection and serves as an equipment grounding conductor. EMT is not rated for direct burial or wet locations without additional protection.

PVC (polyvinyl chloride) conduit is the standard for underground and outdoor installations. It is waterproof, corrosion-resistant, lightweight, and inexpensive ($0.30-1.50 per foot). PVC joints are solvent-welded for waterproof connections. Rigid metal conduit (RMC) and intermediate metal conduit (IMC) provide the highest mechanical protection for industrial and exposed commercial applications at $2-6 per foot.

• EMT: $0.50-2.00/ft, commercial standard, easy to work, not for direct burial
• PVC: $0.30-1.50/ft, underground and outdoor, waterproof, non-metallic
• Rigid metal (RMC): $2-6/ft, industrial, highest protection, threaded joints
• Flexible metal (FMC): $1-4/ft, tight spaces, equipment connections
• Liquidtight flexible (LFMC/LFNC): $1.50-5/ft, wet locations, equipment whips

Conduit Fill Calculations

NEC Chapter 9 limits the percentage of conduit cross-sectional area that can be filled with conductors. One conductor: 53% fill. Two conductors: 31% fill. Three or more conductors: 40% fill. These limits prevent overheating from restricted air circulation and ensure conductors can be pulled and replaced without excessive force.

For example, three 12 AWG THHN conductors each have a cross-sectional area of 0.0133 square inches (total 0.0399 sq in). At 40% fill, the conduit must have an interior area of at least 0.0998 square inches — met by 1/2-inch EMT (0.122 sq in interior area). Adding a 12 AWG ground wire brings the total to 0.0532 sq in, still within the 40% limit for 1/2-inch EMT. Online conduit fill calculators automate this process.

Bending EMT Conduit

The four basic EMT bends are: 90-degree stub-up, offset, back-to-back, and saddle. A hand bender ($30-60 for 1/2-inch or 3/4-inch) is the only tool needed for most residential and light commercial work. Each bender is marked with specific reference points for consistent, accurate bends. The key measurement for a 90-degree stub-up is the take-up — the distance from the mark on the conduit to the back of the bend, which varies by conduit size.

NEC 358.26 limits EMT to a maximum of four 90-degree bends (360 degrees total) between pull points. This ensures conductors can be pulled through the conduit without excessive friction. If a run requires more than 360 degrees of bending, install a pull box to create an intermediate access point. In practice, keeping bends to a minimum reduces both installation time and future wire-pulling effort.

Underground Conduit Installation

PVC Schedule 40 or 80 is the standard for underground electrical conduit. NEC 300.5 specifies minimum burial depths: 24 inches for direct-buried cable, 18 inches for rigid or intermediate metal conduit, 18 inches for PVC under a concrete slab, and 24 inches for PVC in all other locations. Under driveways and areas subject to vehicle traffic, 24 inches minimum regardless of conduit type.

Underground conduit runs should include a separate ground wire (not relying on the conduit as a grounding path), drainage provisions at low points, expansion fittings for runs over 100 feet (PVC expands and contracts with temperature), and pull strings for future wire additions. Marking tape installed 6-12 inches above the buried conduit warns future excavators of its presence.

Choosing the Right Conduit for Each Application

Exposed interior runs (commercial, garage, workshop): EMT is the standard. It is easy to install, provides good protection, and is accessible for future modifications. Exposed exterior runs: rigid PVC or RMC, depending on required mechanical protection and local code. Underground runs: PVC Schedule 40 for most applications, Schedule 80 where exposed above grade.

Connections to equipment (HVAC units, motors, transformers): flexible metal conduit (FMC) in dry locations, liquidtight flexible (LFMC) in wet locations. The flex allows equipment vibration without stressing rigid connections. Inside finished walls: NEC generally allows NM cable (Romex) in residential applications, eliminating the need for conduit. Conduit inside walls is required in some commercial and multi-family construction.