DC fast charging (DCFC) installations operate at power levels of 50 to 350 kilowatts per charger. At those levels, the electrical infrastructure required is commercial in scale: three-phase service, dedicated transformer circuits in many cases, heavy conduit runs, and protection equipment that goes well beyond what a Level 2 charging station requires.
The engineering and permit requirements for DC fast charging reflect that scale. A permit package that would work for a bank of Level 2 chargers is not adequate for a DC fast charging installation. This post covers what the electrical and structural engineering for a DCFC site needs to include and where permit packages most commonly fall short.
Why DC Fast Charging Requires a Different Engineering Approach
The fundamental difference between DC fast charging and Level 2 charging is power delivery. A Level 2 charger typically delivers 7 to 19 kilowatts per unit from a single-phase or three-phase 240-volt circuit. A DC fast charger delivers 50 to 350 kilowatts per unit from a high-power three-phase source, often at 480 volts.
That difference in power level cascades through every element of the electrical design. Conductor sizes increase. Overcurrent protection equipment is larger and more complex. Service entrance requirements may trigger a utility transformer upgrade. The conduit infrastructure required for a multi-charger DCFC installation is more substantial than that of many commercial buildings of similar footprint.
Electrical Plan Set Requirements
Load analysis and service sizing
The starting point for any DCFC engineering package is a load analysis that establishes the total electrical demand of the planned installation. Each fast charger is a continuous load under NEC Article 625. The design load is calculated at 125% of the charger’s rated amperage for conductor and overcurrent protection sizing.
For a multi-charger installation, demand factor calculations may be applied to reduce the total calculated load for service sizing purposes. Actual simultaneous use rarely reaches 100% of the theoretical maximum, and demand factors that reflect realistic peak usage allow more efficient service sizing without compromising performance. The demand factor methodology must be justified in the calculations and accepted by the serving utility.
Service upgrade and transformer coordination
Most existing commercial sites do not have electrical service adequate for a DC fast charging installation without upgrades. A site with 400-amp, 208-volt three-phase service is not sufficient for even a single 150-kW DC fast charger. The engineering package must document the required service upgrade, the new service entrance equipment, and any transformer changes required.
Transformer changes must be coordinated with the serving utility before design is finalized. Utilities have specific requirements for customer-owned versus utility-owned transformers, connection configurations, and protective equipment. Designing the site around a transformer that the utility will not accept wastes time and requires redesign. Start utility coordination early and confirm the transformer configuration before completing the electrical design.
Single-line diagram
The single-line diagram for a DCFC installation must show the complete electrical path from the utility point of delivery through the service entrance, distribution panel, feeder conductors, individual circuit breakers, conduit runs, and each DCFC unit. All equipment must be identified by make, model, and rating. The diagram must be consistent with the load calculations, conduit schedule, and equipment specifications in every detail. For context on what a complete electrical SLD must include, see our earlier post on EV charging permit plan sets.
Conduit and wiring layout
DCFC installations typically involve significant conduit runs from a central distribution point to each charger location. The conduit layout plan must show all conduit routes, sizes, burial depths for underground runs, junction boxes, pull points, and conduit crossings. Conduit sizing must comply with NEC fill calculations for the conductors installed. For installations with multiple chargers, conduit routing affects both construction cost and permit review complexity.
Short circuit and arc flash analysis
Commercial DCFC installations at the power levels involved typically require a short circuit analysis to verify that the available fault current does not exceed the interrupting rating of the specified overcurrent devices, and an arc flash hazard analysis to establish the incident energy at each piece of switchgear where maintenance personnel may work energized. These analyses are often required by the AHJ for commercial electrical permits and are sometimes also required by the facility owner for OSHA compliance purposes.
Grounding and bonding
The grounding system for a DCFC installation must comply with NEC Article 250 for the service equipment and with the DCFC manufacturer’s specific grounding requirements for each unit. Some manufacturers require dedicated ground conductors at each charger that run separately from the equipment grounding conductor in the circuit conduit. Confirm grounding requirements from manufacturer documentation before drawing the grounding plan.
Structural Engineering Requirements
Charger pad and foundation
DC fast chargers are heavy pieces of equipment, often weighing 1,500 to 3,000 pounds. They require a concrete pad foundation that provides a stable, level mounting surface and anchors the charger against wind and impact loads. The foundation design must account for the charger’s weight, anchor bolt pattern, and any conduit sleeves required for below-grade conduit entry.
For chargers installed in vehicle parking areas, the pad design must also address vehicle impact protection. Bollards or wheel stops are typically required to prevent vehicles from contacting the charger units. Bollard placement and foundation design are included in the structural drawings.
Canopy or shade structure
Many DCFC installations include a canopy over the charging stations for weather protection and to support solar panels that contribute to the site’s energy offset. The canopy structure requires its own structural engineering: load calculations for snow, wind, and the dead load of any photovoltaic panels, foundation design for the canopy columns, and connection detailing at each attachment point. Canopy structures at DCFC sites are often the most engineering-intensive element of the site.
PE Stamp Requirements
PE stamps are required on both the electrical and structural engineering documents for virtually all DCFC permit packages. The electrical documents must be stamped by a licensed electrical PE. The structural documents must be stamped by a licensed structural or civil PE. Both stamps must be from engineers licensed in the state where the project is located. Our engineering services cover both electrical and structural PE stamps in all 50 states. Start a project with our team to discuss your site configuration and engineering scope.
Frequently Asked Questions
What is the difference between Level 2 and DC fast charging from a permitting perspective?
Level 2 charging operates at 240 volts AC and typically requires a standard electrical permit with a simple plan set. DC fast charging operates at higher power levels using three-phase service and requires a full commercial electrical permit package with load analysis, short circuit analysis, PE-stamped electrical documents, and often structural engineering for the charger foundation and any canopy structure.
Does a DCFC installation always require a utility transformer upgrade?
Not always, but frequently. Whether a transformer upgrade is needed depends on the existing service capacity at the site and the total load of the planned DCFC installation. Sites with existing large commercial electrical services may have adequate capacity. Most sites that have not previously been used for high-power commercial loads will need a service upgrade or transformer change.
How long does it take to get a DC fast charging permit approved?
DCFC permit timelines vary widely. The AHJ review for a complete, accurate commercial electrical permit package typically takes two to six weeks. Utility coordination for transformer upgrades can take significantly longer, from two weeks to six months depending on the utility. Starting utility coordination before or simultaneous with the permit application compresses the total timeline.
What is an arc flash analysis and when is it required for EV charging?
An arc flash analysis calculates the incident energy at each piece of electrical switchgear where maintenance work might be performed energized. It establishes the personal protective equipment required for safe work at each location. Arc flash analyses are required by OSHA for commercial electrical systems and are often also required by AHJs for commercial DCFC permit packages.
Do DC fast chargers require special grounding?
Yes. DC fast chargers have specific grounding requirements beyond standard NEC Article 250 compliance. Requirements vary by manufacturer and equipment model. The electrical engineer must review the specific equipment specifications before designing the grounding system, as some manufacturers require dedicated grounding conductors that are separate from the circuit equipment grounding conductors.
References
National Fire Protection Association. NFPA 70: National Electrical Code, Articles 230, 240, and 625.
U.S. Department of Energy. DC Fast Charging Infrastructure Planning Resources.
IEEE. Standard 1584: Guide for Performing Arc Flash Hazard Calculations.