What 29 CFR 1926.416 requires (plain English)
29 CFR 1926.416 sets the general safety requirements for electrical work in construction: protecting workers from the shock, arc-flash, and electrocution hazards that make electricity one of construction's "Focus Four" leading causes of death. Construction sites are especially hazardous because temporary wiring, overhead and underground power lines, wet conditions, and metal tools and scaffolds all increase the risk of contact with energized parts. The standard's central rule is simple and strict: keep workers away from energized circuits unless those circuits are made safe.
The core requirement is that no employer may permit an employee to work in such proximity to any part of an electric power circuit that the employee could contact it in the course of work, unless the employee is protected against electric shock by de-energizing the circuit and grounding it, or by guarding it effectively with insulation or other means. In other words, the default for work near electrical circuits is to de-energize and ground; working near still-energized parts is permitted only when they are positively guarded or insulated, not merely when the worker intends to be careful.
Two supporting duties make this workable. Before work begins, the employer must determine (by inquiry, direct observation, or instruments) whether any part of an energized electric power circuit is so located that work could bring a person, tool, or machine into physical or electrical contact with it, then post and maintain warning signs and advise employees of the location and hazards. And worn or frayed electric cords and cables (a ubiquitous jobsite hazard) may not be used. Together these keep workers, conductive tools, and equipment clear of live parts.