NEC Ampacity Table: Find Wire Conductor Ratings Quickly

by

The National Electrical Code (NEC) provides guidelines for the allowable ampacities of insulated conductors. These ampacity values are based on factors such as conductor size, material, temperature rating, and the number of current-carrying conductors in a raceway or cable. Let’s take a closer look at this topic.

  1. Ampacity Tables:
    • The NEC includes tables that specify the allowable ampacities for different conductor sizes and types. These tables help electrical professionals determine the appropriate wire size for a given application.
    • The ampacity tables consider various factors, including ambient temperature, conductor material (copper or aluminum), insulation type, and installation conditions (wet, dry, corrosive, etc.).
  2. Temperature Ratings:
    • Conductors have different temperature ratings, such as 60°C, 75°C, and 90°C. The ampacity values vary based on the conductor’s temperature rating.
    • For example, a conductor with a 90°C temperature rating can carry more current than one with a 60°C rating.
  3. Number of Current-Carrying Conductors:
    • When multiple conductors are bundled together (e.g., in a raceway or cable), their ampacity may need adjustment.
    • The NEC reduces the allowable ampacity for conductors when there are more than three current-carrying conductors in a raceway or cable.
  4. Examples of Ampacity Tables:
    • The NEC provides tables for copper and aluminum conductors. These tables list ampacity values based on conductor size (AWG or kcmil) and temperature rating.
    • Here are some common conductor sizes and their allowable ampacities (based on the 2002 NEC):
      • 14 AWG: 15-20 amperes (depending on temperature and insulation type)
      • 12 AWG: 20-25 amperes
      • 10 AWG: 30-40 amperes
      • 8 AWG: 40-55 amperes
      • 6 AWG: 55-75 amperes
      • …
      • 2000 kcmil: 385-455 amperes
  5. Notes and Considerations:
    • The ampacity values in the table are based solely on temperature and do not account for voltage drop.
    • Overcurrent protection (such as circuit breakers) should not exceed specific limits based on conductor size.
    • Always follow local electrical codes and regulations when selecting conductors.

Leave a Comment