Electrical Safety and Codes
Electrical Safety and Codes
The Electrical Safety and Codes domain tests how well you apply NFPA 70 (NEC) scope, working-space rules, and job-site safety practices. Expect questions on Article 90 and 110, local amendments, lockout/tagout, PPE, and arc-flash boundaries rather than memorized trivia.
Core rules
- The NEC is a model code adopted by the authority having jurisdiction (AHJ); local amendments control. Article 90.3 makes clear it is not a design manual or instruction sheet.
- NEC 110.26 working space: depth depends on voltage to ground and condition. For 151–600 V to ground, Condition 1 is 3 ft, Condition 2 is 3.5 ft, Condition 3 is 4 ft. Width is 30 in or the equipment width, whichever is greater; height is 6.5 ft.
- Lockout/tagout under OSHA 1910.147 requires isolating energy, applying a lock and tag, and verifying absence of voltage.
- NFPA 70E approach boundaries and arc-rated PPE apply to energized work; de-energizing is the default.
Worked example
A 480Y/277 V panelboard has exposed live parts on one side and a grounded metal wall on the other. Voltage to ground is 277 V, so use the 151–600 V row. A grounded surface opposite live parts is Condition 2, requiring 3.5 ft depth. Do not use the 3 ft Condition 1 value just because the system is under 600 V.
Traps
- Treating the NEC as federal law; the AHJ edition and amendments matter.
- Confusing working space with dedicated equipment space.
- Measuring width only; height and depth also apply.
- Skipping voltage verification after lockout.