Reading Electrical Plans
Symbols, One-Lines, Panel Schedules and the Spec Book
NFPA 70 National Electrical Code, 2023 edition · Reviewed 2026-09-21
Plan-reading items give you a drawing fragment or a description and ask what it shows, what the code requires for it, or which document governs. You cannot look symbols up in the NEC — the code doesn't define them — so this lesson covers the conventions the exam assumes plus the code sections that plan questions lean on (NEC references are to the 2023 text).
1. The document set and who wins a conflict
| Document | What it tells you |
|---|---|
| Site plan (C-sheets) | Service entrance location, utility transformer, underground routes, pole lights |
| Floor plans (E-sheets: lighting, power, systems) | Device locations, circuit numbers, home runs, switching |
| One-line / riser diagram | Service size, main distribution, feeders, transformers, panel names, overcurrent device ratings, fault-current values |
| Panel schedules | Circuit numbers, breaker sizes, loads, phase balance, panel bus rating and main |
| Details & sections | Mounting heights, trench sections, support details |
| Specifications (Division 26) | Materials, methods, quality, submittals, testing — the words behind the pictures |
| Symbol legend / general notes | The key to the drawings — always read first |
Conventions: specifications generally govern over drawings on quality and materials; drawings govern on quantity and location; large-scale details govern over small-scale plans; and where anything conflicts with the NEC, the code is the minimum — a plan cannot lower it (the AHJ enforces it; NEC 90.4).
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