Using the National Electrical Code (NEC ... - nfpa.org

1 Using the National Electrical Code (NEC ) Ampacity Charts: Determining Current-Carrying Capacity of Conductors Various tables and charts indicate conductor ampacity, temperature correction factors, and adjustment factors in nfpa 70 , National Electrical Code (NEC ). This document contains some information to help guide users through the ampacity tables to select the appropriate conductor for their installation. Users can start at the beginning and answer a series of questions throughout the flowchart to help determine the next steps in the process.

2 The text in the diamonds denotes a decision to be made and the text in the rectangles denotes a process to go through for the next step. The tables provided are extracted from the NEC and are intended to help the user gather information. For further details, access the complete 2020 edition of the code at or on the nfpa LiNK platform at D2: Yes Do installation D3: Decision 1 (D1): conditions, such as No No Is the conductor Is the conductor Start insulation type location type, affect size known? temperature rating known?

3 Of insulation? P3: Determine ampacity D6: for given size from Yes If conductor size No Yes applicable column of No P6: Determine load current in is not known, is the amount Table for insulation of current to be carried by accordance with Article 220. temperature rating and the conductor Proceed to D7. Process 1 (P1): P2: Using Table , conductor material. Determine the insulation determine applicable known? Proceed to D4. type by consulting the temperature rating of conductor marking info insulation based on or the manufacturer's installation parameters, Yes information.

4 Such as wet, damp, or dry Proceed to D2. location. Proceed to D3. D4: D7: Is the ambient Is the ambient P7: Determine temperature correction temperature of the temperature of the factor inTable (B)(1) based Yes installation different than 30 C installation different than 30 C Yes on temperature rating of conductor (86 F) for greater than 10 feet (86 F) for greater than 10 feet insulation that will be used and actual or 10% of total circuit or 10% of total circuit ambient temperature of installation. length, whichever is length, whichever is Divide load current by this factor.

5 Smaller? smaller? Proceed to D8. P4: Determine temperature correction factor from Table (B)(1) based on conductor insulation rating and actual No No ambient temperature of installation. Multiply ampacity from Table (P3) by this factor. Proceed to D5. D5: D8: P8: Determine ampacity adjustment Are there more Are there more factor based on total number of than three current-carrying than three current-carrying conductors in raceway, cable, or Yes conductors in the raceway or cable, conductors in the raceway or cable, Yes installed without maintaining spacing or are individual conductors or cables or are individual conductors or cables as specified in (C)(1).

6 Divide load installed without spacing for installed without spacing for current (Step P7 if "Yes" for D7; Step P6. greater than 24 greater than 24 or circuit current if "NO" for D7) by this inches? inches? factor. Proceed to P9. No No P5: Determine ampacity adjustment factor based on total number of conductors in raceway, cable, or installed P9: Using the applicable column in Table based on temperature without maintaining spacing as specified in (C)(1). D9: rating and conductor material, determine conductor size with Multiply ampacity (P4 if "Yes" for D4; P3 if "No" for D4) Continue to next page.

7 Sufficient ampacity to serve the load current, as modified by P7 and by this factor. Proceed to D9. P8, if applicable. Proceed to D9. This information is provided to help users navigate nfpa 70 , National Electrical Code , 2020 edition. It is not intended to be a comprehensive list of requirements under nfpa 70. Check with the local jurisdictions for specific requirements. This does not represent the official position of the nfpa or its technical committees on any referenced topic, which is represented solely by the nfpa documents in their entirety.

8 For free access to the complete and most current version of all nfpa documents, please go to The nfpa disclaims liability for any personal injury, property, or other damages of any nature whatsoever resulting from the use of this information. In Using this information, you should rely on your independent judgment and, when appropriate, consult a competent professional. 2021 National Fire Protection Association / May 2021. Using the National Electrical Code (NEC ) Ampacity Charts: Determining Current-Carrying Capacity of Conductors (Continued).

9 D9: Is the load above 100A or are the terminations Learn More Yes No marked for a conductor size larger than 1 AWG? [See (C)(1).] Get free digital access to the standard at D10: Is the conductor D13: Subscribe to nfpa LiNK for Yes insulation rated at 75 C? Is the conductor Yes digital access to nfpa 70. (Note: 60 C insulation is not insulation rated permitted here.) at 60 C? with enhanced content at No No Engage with our experts and your peers on nfpa Xchange . at D11: D14: Find more resources at Are the terminations Are the terminations Yes marked with a temperature marked with a temperature Yes rating equal to or higher than rating equal to or higher than the rating of the conductor the rating of the conductor insulation?

10 Insulation? No No D12: D15: Does the ampacity Does the ampacity of selected conductor, after of selected conductor, after No the application of adjustment and the application of adjustment and No correction factors, exceed that correction factors, exceed that of the 75 C column for the of the 60 C column for the same size and same size and material? material? Yes Yes The conductor size determined on the Use the ampacity from the 75 C column instead; Use the ampacity from the 60 C column instead; The conductor size determined on the previous page is sufficient.