All electrical conductors and equipment must be approved (as defined in 1926.449). The employer must make sure electrical equipment is free of recognized hazards where death or serious physical harm is a likely result, judging safety on suitability for the use (which listing, labeling or certification for that purpose can show), mechanical strength and durability including the protection an enclosure gives, insulation, heating and arcing effects, classification by size, type, voltage, current capacity and specific use, and other factors that protect workers. Listed, labeled or certified equipment is installed and used according to the instructions in its listing, label or certification. Equipment meant to break current needs an interrupting rating at system voltage adequate for the current it must interrupt. Equipment is firmly secured to its mounting surface, and wooden plugs in holes in masonry, concrete or plaster are not used for mounting; equipment cooled by natural air circulation is installed so walls or neighbouring equipment do not block airflow, with clearance above floor-mounted units and free airflow through ventilating openings. Conductors are joined with splicing devices made for that use, or by welding, brazing or soldering; soldered joints are first made mechanically and electrically secure, and all splices, joints and free conductor ends are insulated to the conductor's level. Parts that arc, spark, flame or throw molten metal in normal operation are enclosed or separated from combustibles. Equipment is not used unless it carries the maker's name, trademark or identifying mark plus needed ratings, durable for the environment. Each disconnecting means required for motors and appliances must be legibly marked with its purpose unless evident, and the same applies to every service, feeder and branch circuit, marked at its disconnect or overcurrent device; markings must be durable. At 600 volts or less: where live parts may need examination or servicing while energized, the working space depth toward them meets Table K-1 (3 feet at 0 to 150 volts under all conditions; 3, 3 1/2 or 4 feet at 151 to 600 volts for conditions a, b, c) and is at least 30 inches wide; working space is not used for storage and is guarded when enclosed live parts are opened in a passageway; at least one entrance is provided; front working space at switchboards or motor control centers with exposed live front parts is at least 3 feet; headroom is at least 6 feet 3 inches. Live parts at 50 volts or more are guarded by enclosure or by location in rooms, behind partitions, on elevated platforms or at 8 feet or more, accessible only to qualified persons; equipment exposed to physical damage gets strong guards; entrances to such areas carry conspicuous signs barring unqualified persons. Over 600 volts: installations in locked vaults, rooms or fenced areas count as accessible only to qualified persons, fences under 8 feet need equivalent isolating features, and entrances are kept locked or watched by a qualified person; installations open to unqualified persons use metal-enclosed equipment or locked areas, with caution signs, vehicle guards and deflecting vent openings. Workspace is at least 6 feet 6 inches high and 3 feet wide, with Table K-2 depths (3 to 12 feet by voltage and condition), 30 inches behind equipment needing rear access, doors opening at least 90 degrees; lighting and controls are placed to avoid live parts; unguarded live parts overhead meet Table K-3 elevations (8 feet 6 inches for 601 to 7,500 volts, 9 feet to 35,000 volts, then 9 feet plus 0.37 inch per kV above 35 kV); and at least one entrance at least 24 inches wide and 6 feet 6 inches high is provided, one at each end of boards wider than 48 inches where practicable.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.