This recommended practice 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 recommended practice include metal-enclosed switchgear as defined by IEEE Std C37.20.1, IEEE Std C37.20.2, IEEE Std C37.20.3 and IEEE Std C37.20.9; metal-enclosed bus as defined by IEEE Std C37.23; medium-voltage ac controllers as defined by UL 347; motor control centers as defined by UL 845; switchboards as defined by UL 891; and metal-enclosed medium-voltage air-insulated circuit breakers for outdoor application defined by IEEE Std C37.04 (see note). This recommended practice applies only to equipment utilizing air or other insulating gas as the primary insulation medium and rated 52 kV ac or below. It applies to both indoor and outdoor equipment; however, special consideration should be given to the building size and construction for indoor applications (not fully addressed by this document). The tests and assessments described in this recommended practice 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 recommended practice 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 recommended practice will be referred to as arc-resistant. NOTE—These circuit breakers are sometimes referred to as dead-tank circuit breakers