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Conductors for most buildings in the United States are sized using the National Electrical Code (NEC). The 2014 NEC now requires that a value be added to the ambient temperature used to determine the ampacity of conductors installed on rooftops. This paper reports the results of a related experimental test (on both energized and non-energized cables) that is conducted on a rooftop of a building located in the desert southwest during the hottest period of the year. The recorded temperature rise of the conductors tested is compared to the temperature adders specified in the Code. The maximum recorded temperature of the energized conductors is also compared to the rated temperature of the conductor insulation.