Adding EV charging to a commercial or multifamily property frequently requires upgrading the electrical panel or the service entrance. The existing panel may lack the capacity, the ampacity, or the available breaker slots to accommodate the new charging load. Determining whether an upgrade is required and designing the upgrade correctly is the first step in any EV charging project. Our EV charging engineering services include load studies, upgrade design, and permit-ready drawings for projects in all 50 states.
How to Evaluate Existing Panel Capacity
The starting point for evaluating an existing panel is the load study, which documents the current connected load and the available capacity in the existing electrical service. The load study examines three things: the main breaker size, which limits how much current can flow from the service entrance into the building; the available ampacity in the conductors between the utility meter and the panel, which may be less than the main breaker size in older installations; and the available breaker slots in the panel, which determines whether new EV circuits can be added without also adding a sub-panel.
Comparing the current connected load to the service capacity determines how much headroom exists for new EV load. A 400-amp service that is currently drawing 200 amps under peak conditions has approximately 200 amps of headroom, which can support multiple Level 2 chargers depending on their amperage rating. A 400-amp service drawing 380 amps under peak conditions has essentially no headroom and requires either a service upgrade or load management.
The load study methodology follows NEC Article 220, which provides standardized demand factors for different load types. Using appropriate demand factors rather than simply summing all connected loads gives a more accurate picture of actual demand and avoids over-sizing the service upgrade. Our commercial electrical engineering team prepares load studies that accurately characterize existing demand so the upgrade is sized correctly.
When Panel Upgrade Is Required vs. Load Management
A panel upgrade is required when the existing service lacks the capacity to support the desired number of chargers at full power even with load management. Load management can reduce the peak demand from EV charging, but it cannot make the service capacity larger than it physically is. If the load study shows that the desired EV load exceeds the service capacity after accounting for load management, a panel or service upgrade is necessary.
Load management is a viable alternative to a full service upgrade when the existing service has some available capacity but not enough to support all chargers at full simultaneous power. By installing smart charging equipment that limits the total charging draw to the available headroom, the project can proceed without infrastructure upgrades. The tradeoff is that charging times are longer when many vehicles charge simultaneously.
Service Entrance Upgrade Process
Utility Coordination
A service entrance upgrade requires coordination with the utility to increase the rated service size. The utility must verify that the distribution transformer and service conductors on their side of the meter can support the larger service. For moderate increases in service size, this coordination is often straightforward. For large increases, particularly those approaching transformer capacity limits, the utility may require transformer upgrades as part of the service entrance upgrade. Our engineers initiate this coordination early so that utility and permit timelines run in parallel. Learn more about EV charging utility coordination.
Meter Base and Service Entrance Conductors
Upgrading the service entrance involves replacing the meter base with one rated for the new service size, replacing the service entrance conductors from the utility point of connection to the meter base, and replacing or upgrading the main disconnect and panel with equipment rated for the new service. All equipment must be listed for the application and appropriate for the service voltage and available fault current at the point of connection.
Inspection and Energization
Service entrance upgrades require an electrical inspection before the utility will reconnect the new service. The inspection verifies that all equipment is properly installed, labeled, and bonded. After the inspection passes, the utility schedules the reconnection, which may involve a service outage. For commercial facilities, the service outage must be coordinated with the building owner and tenants.
Sub-Panel Options for Distributed Charging
When chargers are spread across a large parking area or multiple floors of a parking structure, running individual circuits from the main panel to each charger location may be impractical due to distance and voltage drop. Installing sub-panels closer to the charger clusters reduces the length of the final branch circuits and reduces voltage drop while keeping conductor sizes manageable. Our electrical engineering team designs sub-panel configurations that minimize installation cost while meeting code requirements for voltage drop and conductor sizing.
What the Permit Package Includes
A permit package for an EV charging panel upgrade includes a single-line diagram showing the upgrade from the service entrance through the new panel to the EV circuits, load calculations documenting the existing demand and the new EV demand, specifications for the new service entrance equipment and EV charging hardware, and conduit and wiring details for the new circuits. Some jurisdictions also require a site plan showing charger locations and conduit routing.
Frequently Asked Questions
How long does a service entrance upgrade take from permit to energization?
The timeline from permit submission to energization depends heavily on the jurisdiction and the utility. Permit review for electrical work typically takes two to four weeks. Construction of the upgrade takes a few days for a straightforward service entrance replacement. Utility reconnection scheduling adds one to two weeks in most cases. The full timeline from permit submission to energized chargers is commonly six to ten weeks.
Can I add EV chargers to a Federal Pacific or Zinsco panel?
Panels from these manufacturers have known reliability and safety issues and are generally not approved for additional load. Many jurisdictions and insurance companies require replacement of these panels regardless of whether new load is being added. If your building has one of these panels, a full panel replacement is the appropriate approach rather than attempting to add circuits.
What size breaker does a Level 2 EV charger require?
Most Level 2 EV chargers operate at 208 or 240 volts and require a 40 or 50 amp dedicated circuit with a breaker sized at 125 percent of the charger’s rated amperage per NEC requirements. A 32-amp charger requires a 40-amp breaker (32 amps times 1.25 equals 40 amps). A 40-amp charger requires a 50-amp breaker. Commercial DCFC chargers have significantly higher current requirements and require dedicated circuits designed to the manufacturer’s specifications.
Get Your EV Panel Upgrade Engineered
We provide electrical engineering for EV charging panel upgrades in all 50 states. Submit your project at rightangleeng.com/get-started to get started.
References
National Fire Protection Association. (2023). NFPA 70: Article 230: Services; Article 220: Load Calculations; Article 625: Electric Vehicles. Quincy, MA.
U.S. Department of Energy, Alternative Fuels Data Center. (2024). EV Charging Station Installation. afdc.energy.gov.
Electrical Safety Foundation International. (2022). Residential and Commercial Electrical Safety Guide.