Electrical Safety, Codes, and Standards
Two documents, two purposes
NFPA 70 (the NEC) governs how equipment is installed; NFPA 70E governs how people work on it safely. A frequent trap is a stem describing an installation requirement that offers a 70E article as the answer, or vice versa. OSHA citations generally ride on one of these two standards, so know which one backs a given rule.
Core safety concepts
Candidates must understand the elements of an electrical safety program: hazard identification and risk assessment, job briefing, the energized work permit, lockout/tagout, and PPE selection. Know the shock approach boundaries - limited, restricted, and arc flash - and what each permits. Unqualified persons may not cross the limited approach boundary without an escort; only qualified persons using shock-protective equipment work inside the restricted boundary. The arc flash boundary is defined at 1.2 cal/cm², the onset of a second-degree burn - not at whatever the PPE is rated for.
Arc-rated PPE and categories
PPE Category 1 = 4 cal/cm², Category 2 = 8, Category 3 = 25, Category 4 = 40. Category numbers are not cal/cm² values; mixing them up is the most common distractor. An incident-energy analysis supersedes the 70E tables whenever one exists. Work is permitted without an energized work permit only under a "normal operating condition" - properly installed, maintained, and used per its listing and labeling, with no evidence of impending failure.
Rule of thumb
Any task requiring a panel to be opened for live troubleshooting starts at minimum arc-rated clothing plus a face shield; if calculated incident energy exceeds the label rating, de-energize.