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NEC Wire Ampacity in 2021

Posted by Rick Regole on June 01, 2020 | Updated on September 17, 2020

NEC Wire Ampacity Standards

NEC wire ampacity standards are updated every three years. The National Electric Code (NEC) is a standard set of rules for safe electrical design, installation and inspection. The NEC regularly makes necessary revisions to these rules to ensure that standards evolve alongside technology. One of those benchmark years was 2020 and those standards will continue to apply as we move into 2021.

Specifically, we're focusing on the significant changes that have impacted wire ampacity since the last update. Wire ampacity (a wire’s current-carrying capacity) can vary greatly depending on the application and exposure to ambient temperature. If miscalculated, the risk for cable failure, fire, and equipment damage increases exponentially.

Unfortunately, the difficulty of using and understanding certain NEC articles (including ampacity tables) has long been a chief complaint. As such, their 2020 edition aims to clarify and simplify information. There were 3,730 public comments submitted for consideration, sparking conversations that largely focused on:

  • GFCI protection
  • Emergency power disconnects
  • Code organization
  • Reorganization for overvoltage protection

Some of the most noteworthy changes regarding NEC wire ampacity standards resulted from the significant restructuring of Article 310 (Conductors for General Wiring). In the NEC 2020 edition, articles 310 and 328 were consolidated to simplify information and improve usability. Here are the top changes resulting from this restructure that you need to know as we move into 2021. 

NEC Wire Ampacity Standards

  • MV cable requirements moved from Article 310 into a new article—Article 311. Moving forward, Article 310 is for conductors no more than 2,000 volts, while Article 311 (Medium Voltage Conductors and Cables) is for conductors over 2,000 volts.
  • Article 328 (Medium Voltage Cable) was deleted to eliminate information overlap and simplify guidelines. Some of the requirements previously listed in Article 328 were added to the new Article 311.
  • The Ampacity Table, formerly known as 310.15(B)(16), has been renamed as Table 310.16 through Table 310.21.
  • Ampacity Tables for conductors over 2,000 volts can be found in Article 311. New text was added to 310.15(A) regarding ampacities for sizes not outlined in the Ampacity Tables.
  • The word “allowable” was removed from many of the titles and text surrounding the ampacity tables to increase clarity.
  • The Conductor Applications and Installations table was moved from Part III (Table 310.104(A)) to Part II (Table 310.4) to make the information more user-friendly.

Even the best attempts at simplifying electrical codes can prove challenging to understand. In addition to becoming familiar with the latest NEC updates, wise product engineers also partner with a trusted cable and connector manufacturer who can help ensure that wire ampacity aligns with the intended application.

For more information about wire ampacity, check out the iCONN Systems Ampacity Guide.




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