Commercial electrical plan review is more demanding than residential review because the systems are larger, the fault currents are higher, and the coordination between overcurrent protective devices must be documented on the drawings. The NEC requirements that generate the most plan review comments on commercial projects are concentrated in a few areas: panel schedule completeness, feeder and service sizing per Article 220 demand calculations, short-circuit current ratings per Article 110, and grounding per Article 250. These are the errors that plan reviewers check first.
Panel schedule errors
Incomplete panel schedule information
NEC Section 408.4 requires that panelboards be provided with a circuit directory that identifies the purpose or use of each circuit. But plan reviewers check far more than just the circuit labels. A complete panel schedule on commercial drawings must include the panel designation, supply voltage and phase, main breaker or main lug rating, bus rating, the circuit number for each breaker, the breaker size (ampere trip rating), the number of poles, the connected load for each circuit (in VA or watts), the circuit description, and the wire and conduit size for each circuit.
The most common panel schedule error is omitting the connected load values for individual circuits. Without the per-circuit load, the plan reviewer cannot verify that the branch circuit conductors are sized for the load, that the panel is not overloaded, and that the demand calculation supporting the feeder size is accurate. Another frequent error is showing breaker sizes without corresponding wire sizes. NEC Table 310.16 ties conductor ampacity to wire gauge, and the plan reviewer checks that every breaker/wire combination on the schedule is consistent with the table.
| Item | NEC reference | Common error |
|---|---|---|
| Circuit directory (descriptions) | 408.4 | Vague labels like 'spare' or 'misc' for active circuits |
| Connected load per circuit | 220.10 | Omitted; reviewer cannot verify conductor sizing |
| Wire and conduit sizes | 310.16, Chapter 9 Tables | Wire shown but conduit omitted, or vice versa |
| Bus rating vs. main breaker | 408.36 | Bus rated at 225A with 200A main; no issue, but must match NEC |
| Voltage and phase | 408.4 | Single-phase panel fed from three-phase source not noted |
| Total demand load | 220.82-220.87 | Connected load shown but demand factor not applied |
Panel load exceeding bus rating
NEC Section 408.36 requires that panelboards be protected by an overcurrent device having a rating not greater than the panelboard bus rating. The connected load on a panel schedule may exceed the bus rating if demand factors per NEC Article 220 Part III or Part IV reduce the calculated demand below the bus ampacity. But the demand calculation must be shown on the drawings or in a separate calculation sheet referenced on the panel schedule.
The error is a panel schedule showing a total connected load that exceeds the main breaker or bus rating without a corresponding demand calculation that demonstrates the actual demand is within the rating. Plan reviewers will reject a panel schedule that shows 250A of connected load on a 200A panel unless the demand calculation is provided and the calculated demand is 200A or less.
Feeder and service sizing
Demand calculation errors per NEC Article 220
NEC Article 220 provides the methods for calculating branch circuit, feeder, and service loads. Part III covers general demand factors for feeders. Part IV covers optional calculations for certain occupancy types. The demand calculation must be provided on the drawings or in a supporting document referenced on the electrical plans.
The most common demand calculation error is applying demand factors to load types that do not qualify. NEC Table 220.42 permits demand factors for general lighting loads based on occupancy type: office buildings can apply 50% demand to lighting loads over 20,000 VA. But the demand factor applies only to the general lighting load calculated from Table 220.12 (unit load per square foot), not to specific equipment loads, receptacle loads beyond the first 10 kVA (NEC Section 220.44), or motor loads.
Another frequent error is not applying the correct demand factor for kitchen equipment in commercial occupancies. NEC Table 220.56 provides demand factors for commercial cooking equipment based on the number of pieces: 6 or more units qualify for a 65% demand factor. Plan reviewers verify that the demand factors used on the calculation sheet match the NEC tables and that the resulting feeder size (per NEC Table 310.16 at the applicable temperature rating) is shown correctly on the one-line diagram.
Short-circuit current rating
Missing or inadequate available fault current documentation
NEC Section 110.24 requires that the maximum available fault current at the service entrance be documented on the service equipment. The available fault current determines the required interrupting rating of the overcurrent protective devices (NEC Section 110.9) and the short-circuit current rating (SCCR) of the equipment (NEC Section 110.10). If the available fault current exceeds the interrupting rating of any device in the system, the installation does not comply.
The most common error is showing the available fault current at the service entrance but not carrying the calculation downstream to distribution panels and large motor loads. The fault current at a downstream panel is lower than at the service due to impedance of the feeder conductors, but it must still be calculated and compared against the equipment ratings. Plan reviewers check that the fault current study covers the entire distribution system, not just the service point.
NEC Section 110.24(B) requires that the available fault current be recalculated when modifications are made to the electrical installation that affect the fault current. For new construction, this means the fault current study must be based on the actual utility transformer data. A common error is using a generic assumption (e.g., "assume infinite bus at the transformer secondary") that overstates the available fault current. While this is conservative for interrupting rating purposes, it may lead to unnecessarily expensive equipment selections. Plan reviewers may accept an infinite bus assumption but will note it if the utility data is available and should be used.
Overcurrent protection coordination
Missing coordination study reference
NEC Section 240.12 requires that overcurrent protective devices in buildings with a fire pump or in certain healthcare occupancies be selectively coordinated. NEC Section 700.32 requires selective coordination for emergency systems. NEC Section 701.27 requires selective coordination for legally required standby systems. Selective coordination means that when a fault occurs on a branch circuit, only the breaker closest to the fault opens, while upstream breakers remain closed.
The plan review error is showing a one-line diagram with multiple levels of overcurrent protection (main, distribution, branch) without providing a coordination study or referencing one on the drawings. For systems that require selective coordination, the plan reviewer will issue a comment requiring the coordination study. Even for systems where selective coordination is not code-required, a coordination study reference on the drawings demonstrates that the designer has verified the breaker/fuse time-current curves do not overlap in a way that causes unnecessary upstream tripping.
Grounding and bonding
Grounding electrode system errors
NEC Article 250 Part III requires a grounding electrode system at each building or structure served. Section 250.50 requires that all grounding electrodes present at the building (metal water pipe, structural steel, concrete-encased electrode, ground rods) be bonded together. The grounding electrode conductor must be sized per Table 250.66 based on the size of the service entrance conductors.
The most common grounding error on commercial drawings is showing a single ground rod as the grounding electrode system without bonding to other available electrodes. If the building has a concrete foundation with rebar (which qualifies as a concrete-encased electrode per Section 250.52(A)(3)), that electrode must be included in the grounding electrode system. Plan reviewers check the foundation drawings against the electrical grounding plan to verify that all available electrodes per Section 250.52(A) are identified and bonded.
Another frequent error is undersizing the grounding electrode conductor. NEC Table 250.66 sizes the conductor based on the largest service entrance conductor. A 400A service with 500 kcmil copper conductors requires a 1/0 copper grounding electrode conductor. Showing a #6 copper ground (which is adequate for a 200A residential service) on a 400A commercial service is an immediate plan review correction.
Emergency and standby power
Missing transfer switch and emergency circuit identification
NEC Article 700 (Emergency Systems) and Article 701 (Legally Required Standby Systems) require that emergency and standby circuits be clearly identified on the drawings and physically separated from normal power wiring. Transfer switches must be shown on the one-line diagram with their ampere rating, the load served, and the transfer time.
Plan reviewers flag two errors repeatedly. The first is emergency and standby loads that are not separated from normal loads on the panel schedules. NEC Section 700.10(B) requires that emergency circuit wiring be kept entirely independent of all other wiring, which means emergency loads must be on dedicated panels, not mixed with normal loads on a shared panel. The second is not showing the generator or battery system sizing calculation. NEC Section 700.4 requires that the emergency power source have adequate capacity for all connected emergency loads. The calculation must account for motor starting inrush, not just the running load.
| Item | NEC reference | Common error |
|---|---|---|
| Transfer switch on one-line | 700.5, 701.5 | Transfer switch not shown or missing rating |
| Emergency panel schedule | 700.10(B) | Emergency loads mixed with normal loads on shared panel |
| Generator sizing calculation | 700.4 | Running load shown but motor starting inrush not included |
| Selective coordination | 700.32 | No coordination study for emergency system OCPDs |
| Circuit identification | 700.10(A) | Emergency circuits not labeled on panel schedules and plans |
Voltage drop
Not documenting voltage drop calculations
NEC Section 210.19(A) Informational Note No. 4 and Section 215.2(A)(4) Informational Note No. 2 recommend that voltage drop not exceed 3% on branch circuits and 5% total (feeder plus branch circuit). While these are informational notes rather than mandatory requirements, many jurisdictions enforce them as requirements, and plan reviewers in those jurisdictions will issue comments if the voltage drop calculation is not provided.
The most common error is not providing a voltage drop calculation for long feeder runs. A 200-foot feeder run at full load on a 208V system may exceed the 2% feeder voltage drop recommendation depending on the conductor size. The plan reviewer checks the one-line diagram for long runs (typically anything over 100 feet) and verifies that the conductor size shown on the drawings keeps the voltage drop within limits. If no calculation is provided, the reviewer will request one.
Catching commercial electrical errors before submittal
Commercial electrical plan review covers the panel schedules, the one-line diagram, the demand calculation, the fault current study, the grounding plan, and the emergency power system as an interconnected package. The errors that generate the most revision cycles are the ones that span multiple documents: a demand calculation that does not match the panel schedule totals, a feeder size on the one-line diagram that does not match the demand calculation, or an available fault current at the service that exceeds the interrupting rating of a downstream breaker. Reviewing the electrical drawings, schedules, and calculations against the NEC in a single pass catches these cross-document errors before the plan reviewer does.