Reading Electrical Plans: Symbols, One-Lines, Panel Schedules and the Spec Book
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.
NFPA 70 National Electrical Code, 2026 edition · Reviewed 2026-09-19
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.
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).
This is where the public part ends.
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