Panel schedule errors and how to catch them
The most common errors in electrical panel schedules and a checklist for catching them at review
Why Panel Schedules Matter
Panel schedules are how electrical loads get organized, sized, and protected. A bad panel schedule produces nuisance tripping, AIC mismatches that fail inspection, and code violations that are expensive to fix after installation. Most electrical drawing review starts at the panel schedule because errors there cascade into every other electrical drawing.
What a Complete Panel Schedule Includes
- Panel name, location, served-by upstream device
- Voltage, phase, number of wires
- Bus rating (amps)
- Mounting (surface or flush) and NEMA enclosure type
- AIC rating
- Main breaker or main lugs only
- Circuit-by-circuit list with: number, breaker size, poles, conductor size, load description, connected load (VA)
- Phase loading totals A, B, C
- Connected load, demand load with demand factors applied
- Spare and space allocations
- Notes for special conditions (GFCI, AFCI, dedicated, EM)
The Most Common Errors
- Phantom circuits, circuits listed in the schedule with no corresponding device on the plans
- Orphan loads, devices on the plans not assigned to any circuit
- Wrong demand factors, using 100% demand on loads that should have NEC demand factor reduction
- Missing demand factors, using NEC demand reductions where the local AHJ requires 100% demand
- AIC rating below available fault current at panel location
- Continuous loads not multiplied by 1.25 for conductor and OCPD sizing
- Phase imbalance exceeding good-practice limits (typically > 10%)
- Conductor size mismatched with breaker (e.g., 12 AWG on a 30 A breaker without exception)
- Voltage drop calc missing or exceeding design limit
- GFCI/AFCI requirements not flagged where NEC requires
- Emergency or essential circuits not separated from normal
Demand Factor Misuse
Demand factors permit conductors and OCPD to be sized for the load expected to run simultaneously, not the connected load. NEC defines demand factors by occupancy and load type (dwelling lighting, motors, kitchen equipment, electric range, etc.). The two most common errors are applying demand factors where the code does not allow them (e.g., commercial continuous lighting), and failing to apply them where the code does allow them, resulting in oversized services.
AIC Rating Mismatches
- Calculate available fault current at every panel based on utility supply and feeder impedance
- Verify panel AIC rating exceeds available fault current
- Verify branch breaker AIC ratings exceed available fault current at that panel
- For series-rated combinations, document the series rating and the tested combination
- Label panels with available fault current per NEC 110.24
Use a checklist that requires the reviewer to trace each labeled device on the lighting and power plans back to its circuit on the panel schedule, and each circuit on the panel schedule back to a device on the plans. The two-way trace catches both phantom circuits and orphan loads neither of which is visible if you only review one direction.
Continuous vs. Non-Continuous Loads
Continuous loads (operating 3 hours or more) require conductors and OCPD sized at 125% of the load per NEC 210.19 and 210.20. Common continuous loads include commercial lighting, electric signage, and continuous-duty equipment. Failing to apply the 1.25 multiplier is one of the most frequent panel schedule errors caught in plan review.
Phase Balance
- Distribute single-phase loads across A, B, C to balance within 10%
- Three-phase loads automatically balanced
- Calculate phase loading totals and verify on the schedule
- Identify imbalanced panels for re-circuit assignment
Keep exploring
More guides on electrical drawing review and code compliance.