This guide establishes methods by which equipment may be tested for resistance to the effects of arcing due to an internal fault. Equipment types covered in this guide include metal-enclosed switchgear as defined by ANSI/IEEE C37.20.1TM, C37.20.2TM and C37.20.3TM; metal-enclosed bus as defined by ANSI/IEEE C37.23 TM; medium-voltage ac controllers as defined by UL 347: motor control centers as defined by UL 845; and switchboards as defined by UL 891. This guide applies only to equipment utilizing air as the primary insulating medium and rated 38 kV ac or below. It applies to both indoor and outdoor equipment; however, special consideration must be given to the building size and construction for indoor applications (not fully addressed by this document).The tests and assessments described in this guide are only applicable to arcing faults occurring entirely in air within the enclosure when doors and covers are properly secured in accordance with the rated Accessibility Type. This guide does not apply to arcing faults that occur within components of the equipment, such as instrument transformers, sealed interrupting devices, fuses, and so on.Designs that meet the requirements of this guide are referred to as arc-resistant.