A failed electrical inspection doesn't always mean bad wiring. More often it means the service was sized without a proper load calculation, and no one caught it until the inspector did. Here's what a PE electrical engineer actually checks, and why it matters before you build.
The electrician pulls the permit, installs the panel and calls for inspection. The inspector reviews the load calculation and fails it. Not because anything was wired wrong. Because the service is undersized for what the building actually demands, and nobody ran the math before the work started.
This happens on residential and commercial jobs alike. The electrical work is fine. The panel schedule looks reasonable. But without a proper load calculation, the plan reviewer or inspector has no verified basis for approving the service size. In jurisdictions that require a calculation with the submittal, that alone can stop the job.
Understanding why panels fail starts with understanding what a load calculation is, what it covers, and why the number on the main breaker isn't the whole story.
What an Electrical Load Calculation Actually Is
A load calculation is a formal analysis, governed by NEC Article 220, that determines the total electrical demand a building places on its service. It accounts for every load: lighting, receptacles, HVAC equipment, appliances, water heaters, EV chargers, solar and storage, generators and any special equipment. The result tells you the minimum service size the building needs to operate safely and to code.
For dwellings, the NEC provides two main approaches: the standard method, which builds up the load item by item with the code's demand factors, and the optional method, which uses a different set of demand factors that recognize not every load runs at full power at the same time. Both are legitimate. Neither is a guess. The method affects the result, and applying demand factors incorrectly produces a calculation that looks reasonable but doesn't satisfy code.
The panel size is the conclusion of the calculation, not the starting point. When you size the panel first and calculate second, you're working backwards.
The Four Reasons Panels Fail Inspection
1. No Calculation on File
Many jurisdictions require a load calculation as part of the permit submittal for new construction, additions and service upgrades, and some require it to be sealed by a PE. If the permit was pulled without one, or the calculation was done informally and never documented, there's no verified basis for the service size. The service may be adequate, but without documentation proving it, it gets flagged.
This is common when the panel was sized from experience and past jobs rather than the formal NEC calculation. Experience is valuable, but it isn't documentation, and plan reviewers know the difference.
2. The Service Is Genuinely Undersized
When the calculation is run correctly and the service still comes up short, it's usually because demand grew past what was planned. The usual culprits are EV charging, added HVAC equipment, electric water heaters replacing gas, or solar with battery backup. Each changes the load calculation, and each should be checked before the upgrade is permitted.
Adding an EV charger or solar? Check the calc first. The NEC treats EV charging equipment as a continuous load, which raises how much capacity it takes up in the calculation. Solar and battery storage add their own rules for how the system connects to the service and what the panel busbar can accept. Either one can push an existing residential service past its limit, so update the load calculation before you apply for the permit.
3. Panel Schedule Doesn't Match the Drawings
Even with a correct calculation, a common failure is a panel schedule that doesn't reconcile with the architectural or mechanical drawings. If the drawings show a 5-ton condenser but the panel schedule has a breaker sized for a 3-ton unit, the reviewer flags it. The fix isn't rewiring. It's coordinated documents where the electrical matches what's actually being built.
This usually happens when the electrical plans are produced in isolation from the rest of the set. A PE electrical engineer working from the full drawing set, not just the electrical sheets, catches these mismatches before submittal instead of at inspection.
4. Demand Factors Applied Incorrectly
NEC demand factors let engineers reduce the calculated load for certain systems based on the likelihood that not everything runs at once. Applied correctly, they let a building use a smaller service than the sum of every connected load would suggest. Applied incorrectly, or to loads that don't qualify, they justify an undersized service that doesn't actually meet code.
This is one of the most common errors in calculations done without an engineer. The math works. The formatting looks professional. But the demand factors are misapplied, and a sharp plan reviewer, or the utility during service review, will catch it.
What a PE-Sealed Load Calculation Covers
- General lighting and receptacle loads. Calculated by square footage using the NEC Article 220 unit loads for the occupancy type.
- HVAC and mechanical equipment. Taken from nameplate data or the mechanical schedules, not estimated, including the code's added allowance for the largest motor.
- Kitchen and laundry appliances. Residential and commercial kitchens have their own demand factors and fixed appliance rules for each occupancy.
- EV charging, solar and generators. Each has specific NEC requirements for how it's counted in the calculation and how it connects to the service.
- Total demand and service size confirmation. The final output: the minimum service size required, checked against the proposed panel, with the PE's seal and license number.
Why Multi-Family and Commercial Projects Are Higher Risk
The stakes go up on multi-family and commercial projects. A miscalculated service on an apartment building doesn't just affect one panel. It affects the building's service entrance, the utility's transformer sizing and every tenant's service. Utilities typically ask for load information as part of the service application, and if your numbers and the utility's don't agree, the application stalls and so does construction.
Commercial projects add more: occupancy-based lighting loads, demand factors for commercial kitchen equipment, emergency and standby power, and often extra coordination with the utility. That's work for a PE electrical engineer with commercial experience, not a guess on the panel schedule.
What A1 Engineering Provides
Electrical engineering is A1 Engineering's core. Nick Burton, PE, is a licensed electrical engineer in Texas, Florida, Georgia and North Carolina. A1 produces and seals load calculations for residential, multi-family and commercial projects, checked against the architectural and mechanical drawings and formatted for the jurisdiction's submittal requirements.
Beyond the load calc, A1 prepares panel schedules and the electrical engineering for solar PV, EV charging, generators and backup power, and multi-family services. If your drafter or designer drew the electrical sheets, A1 can review them, redline them with code citations and seal them once they're right.
See also What Is an MEP Drawing Set? for how the electrical fits with the rest of the set.
If you need a sealed load calculation, a panel schedule review or electrical engineering for a new build, addition or upgrade, send your plans to A1 Engineering. If an inspection is coming up fast, call (214) 382-9584.