Electrical drawings carry a unique review burden. The NEC is one of the most frequently updated codes in construction, with new editions every three years, with hundreds of changes each cycle. An electrical reviewer isn't just checking current requirements; they're checking against whichever edition the jurisdiction has adopted, which might be 2020 or 2023 depending on the state.
Here are the NEC violations that generate the most correction notices in plan review, and why they persist even among experienced electrical engineers.
1. Panel schedule math errors
Panel schedules are where the design meets the numbers, and the numbers need to add up. The most common errors: branch circuit loads that don't match the connected load calculations, phase balancing that's off by more than the AHJ allows (typically 10 to 15% between phases), and total panel demand that exceeds the main breaker rating.
NEC Article 220 governs load calculations, and Article 408 covers panelboard requirements. The reviewer checks both: are the individual loads calculated correctly per 220, and does the panel as shown in the schedule comply with 408?
2. Conductor sizing vs. overcurrent protection
NEC Table 310.16 (formerly 310.15(B)(16)) is the most referenced table in the code - it lists ampacities for conductors at 30°C ambient. The violation: conductors sized for the load but not coordinated with the overcurrent protection device. A 20A circuit on #12 AWG copper is correct at 75°C terminal rating, but if the engineer spec'd #14 AWG to save copper cost without checking the breaker coordination, it fails.
| Conductor | 60°C Ampacity | 75°C Ampacity | Max OCPD |
|---|---|---|---|
| #14 AWG Cu | 15A | 20A | 15A |
| #12 AWG Cu | 20A | 25A | 20A |
| #10 AWG Cu | 30A | 35A | 30A |
| #8 AWG Cu | 40A | 50A | 40A* |
| #6 AWG Cu | 55A | 65A | 55A* |
*Per NEC 240.4(D). Terminal temperature ratings and derating factors may further reduce allowable ampacity.
The subtlety is terminal temperature ratings. Most equipment terminals are rated for 75°C, but some, especially older or smaller equipment, are rated for 60°C. Using the 75°C column for a conductor landing on a 60°C terminal is a code violation, and it's one that reviewers specifically look for.
3. AFCI and GFCI requirements
Arc-fault circuit interrupter (AFCI) and ground-fault circuit interrupter (GFCI) requirements expand with nearly every NEC edition. The 2023 NEC requires AFCI protection in virtually all dwelling unit areas (210.12) and GFCI protection in an expanding list of locations including kitchens, bathrooms, laundry areas, garages, and outdoor outlets (210.8).
A project designed to NEC 2020 has different GFCI requirements than one designed to NEC 2023. The reviewer checks against the edition adopted by the jurisdiction, not the latest edition. Engineers who work across states frequently get tripped up by this.
4. Short-circuit current rating (SCCR)
NEC 110.10 requires that equipment be rated for the available fault current at its location. This means the engineer needs to know the available fault current at every panel, disconnect, and piece of equipment, and the equipment's SCCR must meet or exceed it.
The issue: fault current calculations are often done for the main service but not carried through to downstream panels and equipment. A panel with a 14 kA SCCR rating installed where 22 kA is available is a code violation and a safety hazard. The 2023 NEC added Section 110.24(B) requiring fault current documentation on field-installed labels.
5. Voltage drop
NEC 210.19(A) Informational Note No. 4 recommends limiting voltage drop to 3% on branch circuits and 5% total (feeder + branch). While technically advisory, most AHJs enforce it as a requirement, and many specification sections mandate it.
Voltage drop calculations are frequently missing from the drawings entirely. When they are shown, the common error is calculating based on the circuit length (one-way distance) rather than the conductor length (which accounts for the return path). For single-phase circuits, the conductor length is twice the circuit length.
6. Working space clearances (NEC 110.26)
Article 110.26 requires minimum working space in front of electrical equipment - 36 inches deep for most voltages, 30 inches wide or the width of the equipment (whichever is greater), and 6.5 feet of headroom. This is one of the most frequently violated requirements in the field, and reviewers check the drawings for it.
The drawing review catches the obvious cases, like a panel scheduled for a closet that's too shallow, or a mechanical unit shown within the clearance zone. The field catches the rest, but by then the change order is expensive.
7. Arc flash documentation
NFPA 70E and NEC 110.16 require arc flash warning labels on equipment likely to require examination, adjustment, servicing, or maintenance while energized. The labels must include the available incident energy or the required PPE category.
An arc flash study is typically a separate deliverable from the electrical drawings, but the drawings should reference it and show label locations. When the arc flash study isn't complete at the time of permit submittal (which is common), the reviewer may condition the permit on receiving the study before energization.
8. Emergency and standby power
NEC Articles 700 (Emergency), 701 (Legally Required Standby), and 702 (Optional Standby) have specific requirements for transfer switches, circuit identification, and separation from normal power wiring. The most common violation: emergency circuits routed in the same raceway or enclosure as normal circuits, which violates 700.10(B)(1).
Why electrical reviews take longer
Electrical drawings have more cross-references than any other discipline. The one-line diagram references the panel schedules. The panel schedules reference the load calculations. The load calculations reference the equipment specs. The equipment specs reference the fault current study. Each link in that chain needs to be consistent, and a change anywhere propagates everywhere.
Automated first-pass review helps because it checks these cross-references systematically - the same way a reviewer does, but without the fatigue factor that sets in on the third panel schedule.
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