An electrical wire ampacity chart can be found in the National Electrical Code Handbook, NFPA 70. The NEC Handbook is published by the National Fire Protection Association, an international non-profit organization. The NEC Handbook table 310.15(B)(16), Allowable Ampacities of Insulated Conductors, can be obtained as a downloaded document from NECConnect.org.
Extracts and adaptations of the NEC Handbook ampacity table are published on numerous web sites of electrical wire manufacturers and electrical component suppliers. Adopted for electrical wiring standards in all 50 U.S. states, the NFPA NEC contains guidelines for the electrical current-handling capacity, or ampacity, of conductors according to their material type, temperature rating and size as of 2015.
The NEC Handbook table 310.15(B)(16) includes two basic conductor material types, copper and aluminum, with copper-clad aluminum included within the aluminum type. Each material type is sub-categorized by temperature ratings of the conductor, the lowest safe temperature that a specific product is rated for use. Rows of the table list conductor sizes for each material type and temperature combination using the American Wire Group, or AWG, standard diameters. The ampacity of a conductor is read from the table by referencing the AWG diameter of interest and the specific temperature rating for the conductor material type. Ampacity values of the table are in units of amperes, or amps.