Raceway and Conduit Notes

Raceway/Conduit

  • Purpose
    • Protect conductors
    • Support conductors
    • Provide access to conductors
    • Reduce risk of fire
    • Metal raceway can be used as grounding conductor (but we won’t do that)

Metal Conduit and Tubing (Non-Flexible)

  • EMT (Electrical Metal Tubing) – NEC 358
    • Also called “thin wall conduit”
    • Tubing not threaded, joined by compression or set screw fittings
  • IMC (Intermediate Metal Conduit) – NEC 342
    • More protection from physical damage
    • Threaded fittings
  • RMC (Rigid Metal Conduit) – NEC 344
    • Threaded fittings
    • Maximum protection from physical damage

Metal Conduit and Tubing (Flexible)

  • FMC (Flexible Metal Conduit) – NEC 348
    • Commonly called “Greenfield”
    • Generally for final connections, specifically those subject to movable devices (lights), or vibration (motors)
    • Limit length to less than 6 feet.
  • LFMC (Liquid-tight Flexible Metal Conduit) – NEC 350
    • PVC jacketed to allow for outdoor use

Non-Metallic Conduit and Tubing

  • ENT (Electrical Non-metallic Tubing) - NEC 362
    • Most often blue or orange flexible tubing
    • “Smurf tube” or “Smurf pipe”
    • Can’t be used in return air plenums
  • PVC (Rigid polyvinyl Chloride Conduit) - NEC 352
    • Comes in Schedule 40 and Schedule 80
    • Lightweight, inexpensive
    • Typically used for below grade installations
    • Not allowed in return air plenums

Raceway Sizing

  • Generally the smallest allowed by code/common practice is 1/2”
  • Smallest conduit underground is typically 1”
  • NEC Chapter 9
    • Table 1- Limits us to 40% fill
    • Start with Table 5 to determine total area for conductors
    • Then use Table 4 to select appropriate conduit size based on conduit type
  • Annex C-Explanatory material (not code)
    • Based on Tables 1, 4, 5 and 5A in Chapter 9
    • Must use the table that corresponds to the conduit being used