- Good charging design starts with energy and dwell time per vehicle, not with the number of charger boxes.
- Level 2, DC fast and heavy-duty charging place very different demands on service size, space and cost.
- NEC Article 625 treats charging as a continuous load, and California building codes add EV capable and accessibility rules.
- Load management often lets a site serve many chargers from a fraction of their combined rating.
- Utility lead times for service and transformer upgrades are frequently the longest item on the schedule.
- Pathways, spare capacity and phasing let a site grow from a pilot to a full fleet without rework.
- What Is EV and Fleet Charging Infrastructure Design?
- How a Charging Site Works
- Charger Types and Site Models
- Codes, Standards and Utility Requirements
- Applications by Building Type
- Design Process and Deliverables
- Special Cases and Emerging Needs
- Choosing Equipment and Understanding Cost
- Best Practices, Mistakes and Commissioning
- Where Budlong Delivers This
- Related Reading
- Frequently Asked Questions
Electric vehicles have moved from a parking lot amenity to a business system. A delivery fleet that cannot charge by morning cannot run its routes, and an office tower that cannot offer charging risks losing tenants. The challenge for owners is that charging is an electrical, civil, software and utility problem at once, and the chargers themselves are often the smallest part of it. Our commercial electrical services group designs the power systems that make charging sites reliable.
Budlong has worked on building power since 1958, and the transit charging projects in our company history have given us a practical view of what works when many vehicles need energy at the same time. This guide covers the design questions in the order a project meets them, from vehicle duty cycles to commissioning, with attention to the codes that apply in California.
1. What Is EV and Fleet Charging Infrastructure Design?
More than chargers
Charging infrastructure design is the engineering of everything between the utility meter and the vehicle connector. It includes the service and switchgear, transformers, feeders, charger and dispenser layout, trenching and conduit, controls and networking, accessibility and signage, fire protection coordination and the plan for expansion. A site that treats the chargers as a purchase and the rest as an afterthought tends to discover its real costs during construction.
Public, workplace and fleet charging
The design logic differs by use. Workplace and multifamily parking involves long dwell times and many low-power ports. Retail and hospitality sites need shorter stays and visible, easy-to-use equipment. Fleet depots are the most demanding, because the vehicles are the business and the schedule is fixed. A depot design starts from the route, the battery and the departure time.
Why design matters early
Capacity is expensive to add later. Conduit, panel space and transformer pad room placed during the first build cost little compared with trenching through a finished lot. Our view of how electrification reshapes MEP engineering follows the same theme: plan the system the building will need in ten years, not just the one it needs on opening day.
Also Read: The Impact of Electrification on MEP Engineering
2. How a Charging Site Works
The power chain
Power flows from the utility service to main switchgear, through distribution equipment to chargers, and from chargers to vehicles. At each step, a device limits current and protects the one downstream. For AC charging, the charger is a smart outlet and the vehicle contains the converter. For DC charging, the converter is inside the charger cabinet, which is why DC equipment is larger and has higher power.
Power versus energy
Two quantities matter. Power, in kilowatts, sets the size of the electrical equipment and often the utility demand charge. Energy, in kilowatt-hours, is what the vehicle needs to complete its work. A fleet with a long overnight window can deliver a large amount of energy at modest power, and that is the principle behind load management.
An illustrative fleet sizing example
Suppose a depot houses 40 delivery vans, and each returns needing about 60 kilowatt-hours. The total energy is 2,400 kilowatt-hours. Spread over an eight hour overnight window, that is an average of 300 kilowatts delivered, or about 330 kilowatts at the grid once charger losses are included. If every van were fitted with a 19.2 kilowatt Level 2 port and all charged at full power at once, the connected load would be 768 kilowatts. Managed charging can serve the same fleet from a much smaller service, as long as the departure times are met.
| Scenario | Chargers | Approximate peak demand | Comment |
|---|---|---|---|
| Unmanaged Level 2 | 40 ports at 19.2 kW | About 770 kW | All ports at full output together |
| Managed Level 2 | 40 ports, controlled | About 330 kW | Spread across the overnight window |
| DC fast, short turnaround | 10 ports at 150 kW | Up to about 1,500 kW | For vehicles that need quick turns |
The figures are for illustration only. Actual values depend on battery size, efficiency, ambient conditions and the vehicle charge curve.
3. Charger Types and Site Models
Charger classes
| Class | Typical power | Typical use | Electrical implication |
|---|---|---|---|
| Level 1 | Around 1.4 kW | Very long dwell, residential style | Standard receptacle, rarely used for commercial sites |
| Level 2 | Roughly 6 to 19 kW | Workplaces, multifamily, hotels, depots | 208 or 240 volt circuits, many ports per panel |
| DC fast | 50 to 350 kW and above | Short turnaround, public and fleet | 480 volt three-phase feeders, large pads and cabinets |
| Heavy-duty and megawatt-class | Hundreds of kW to over 1 MW | Buses and trucks | Medium-voltage or dedicated transformers, special connectors |
Connectors and communications
Connector standards have been consolidating, with the SAE J1772 AC connector, the CCS combined connector and the NACS connector standardized as SAE J3400 all in service. Sites should specify equipment that supports the connectors their vehicles use and has a path to add adapters or cables. Communication between the charger and the network typically uses the Open Charge Point Protocol, and vehicle to charger communication follows ISO 15118 on newer equipment. Open standards protect owners from being locked into one software provider.
Site models
- Depot charging: dedicated stalls, charged overnight, controlled by a fleet management system.
- Opportunity charging: chargers at route ends or terminals, used during short layovers.
- Destination charging: parking at workplaces, hotels and retail, with moderate power and long stays.
- Hub charging: a mix of DC fast ports for public or shared fleet use.
The US Department of Energy’s Alternative Fuels Data Center is a useful reference for charging terminology and national program information, and the National Renewable Energy Laboratory publishes research on charging demand and grid integration.
4. Codes, Standards and Utility Requirements
Electrical code and product listings
NEC Article 625, published by NFPA as part of NFPA 70, governs EV power transfer systems. It addresses equipment listing, continuous load sizing, disconnecting means, ventilation where needed, and the use of energy management systems. Product listings from UL apply, including UL 2594 for EV supply equipment, UL 2202 for DC charging systems, UL 2231 for personnel protection and UL 9741 for bidirectional equipment.
California building standards
California’s green building standards code, CALGreen, sets mandatory EV capable and charging provisions for new nonresidential and multifamily construction, with the amounts defined by the adopted edition. The California Building Code adds accessibility rules for charging spaces under Chapter 11B. Energy compliance sits within Title 24, Part 6, administered by the California Energy Commission. Our CALGreen MEP guide and the Title 24 compliance checklist explain how these requirements show up in design.
Utility and local approvals
The serving utility controls the service point, metering, transformer and any capacity upgrade. Programs, rates and incentives for charging change often, so owners should confirm current offerings directly with the utility. Fire code and the local authority having jurisdiction may add requirements for signage, clearances, access and indoor installations. State fleet and transit rules also continue to evolve, so confirm current status with the relevant state agency before locking a fleet transition schedule.
Also Read: CALGreen MEP Guide
5. Applications by Building Type
Offices and commercial buildings
Tenants and employees expect charging, and many local rules require some level of installed or EV capable parking. A commercial building typically uses managed Level 2 charging across a garage, sized against the building’s spare capacity. Efficient design also limits operating cost, a theme we explore in our article on reducing operating costs through MEP design.
Multifamily and mixed-use
Residents park for long periods, so many low-power ports shared through load management are usually better than a few fast chargers. Metering and billing per user raise design questions, and our multi-family practice addresses them early.
Airports and aviation
Airports combine passenger vehicles, rental fleets, shuttle buses, ground support equipment and airline operations. Our aviation work includes the LAX bus charging station, where bus schedules, terminal operations and utility coordination all shape the design.
Transit and municipal fleets
Transit depots have large, predictable loads and strict schedules. Projects such as the El Monte Transit Center and the Harbor Gateway Transit Center zero-emission bus charging installations show how many buses can share a managed power system.
Campuses and institutions
Universities, hospitals and public agencies operate mixed fleets and staff parking across large sites. The institutional setting favors phased plans, with trunk conduit and switchgear built first and charger quantities added as the fleet changes.
| Site type | Typical charging approach | Design emphasis |
|---|---|---|
| Office and retail | Managed Level 2, some DC fast | Spare service capacity and accessibility |
| Multifamily | Many shared Level 2 ports | Metering, billing and load sharing |
| Airport | Mixed Level 2, DC fast and bus charging | Utility capacity and operational schedules |
| Transit depot | High-power DC dispensers, managed | Redundancy, resilience and expansion |
| Campus | Phased mix of Level 2 and DC | Conduit backbone and standard equipment |
Planning a charging project?
Share your vehicles, schedule and site, and our engineers will outline the service, layout and phasing options.
Start a charging design conversation
6. Design Process and Deliverables
Needs assessment and duty cycle
The first step is a list of vehicles with battery size, daily energy use, arrival and departure times, and growth forecasts. For public sites, the equivalent is expected usage and dwell time. The assessment decides the charger mix, the quantity and the power level.
Load study and utility coordination
The load study compares the proposed demand to the existing service, using calculated and measured data where available. Our electrical load calculation guide describes the methods. If capacity is short, the options are a service upgrade, load management, on-site storage or a phased schedule. The utility request should go out early with a clear estimate.
Layout and distribution design
Layout covers parking geometry, charger location, cable reach, accessible routes, lighting, bollards, trenching routes and transformer placement. Distribution design includes the one-line diagram, feeder sizing, protective devices and the short circuit and coordination results for the new equipment.
Deliverables
| Stage | Key activities | Deliverables |
|---|---|---|
| Concept | Duty cycle, load estimate, site options | Charging strategy and capacity estimate |
| Schematic design | Utility request, charger mix, phasing | Preliminary layout and one-line diagram |
| Design development | Load study, equipment selection, civil coordination | Coordinated plans and specifications |
| Construction documents | Detailed design, permitting package | Drawings, schedules, controls requirements |
| Construction support | Submittal review, field coordination | Reviewed submittals, field reports |
| Commissioning | Testing, network setup, training | Test reports and operator documentation |
A well-coordinated package aligns with the building design from the start. Our guide to designing for future electrical load expansion shows how to reserve space and capacity.
7. Special Cases and Emerging Needs
Heavy-duty and megawatt-class charging
Trucks and buses draw far more power than cars. Sites may need dedicated medium-voltage service, large pad-mounted transformers and special connectors. Thermal management of cabinets, cable weight and vehicle maneuvering space become major design drivers.
Solar and storage integration
On-site generation and batteries can offset energy, shave peak demand and provide short-term support during outages. They add complexity, including inverter protection and interconnection. The capabilities of our photovoltaic design team and the article on commercial solar PV design describe how generation fits into the site plan.
Backup power and resilience
A fleet that depends on charging also depends on power continuity. Owners should decide which chargers need backup, whether through generators, storage or a microgrid. Our article on resilient MEP systems for climate adaptation outlines resilience thinking for these cases.
Indoor garages and existing buildings
Garages bring structure, ventilation and fire protection coordination, and existing buildings may lack panel space or riser capacity. Surface-mounted conduit, new subpanels and load management can work around constraints, but each needs coordination with the structural and fire teams.
Bidirectional charging
Vehicle-to-building and vehicle-to-grid features can turn parked vehicles into a resource. They require compatible vehicles, equipment listed for bidirectional use, utility interconnection approval and clear operating agreements.
8. Choosing Equipment and Understanding Cost
Selection criteria
- Safety listing and compatibility with the vehicles in service.
- Open communication standards, so the owner is not locked into one network.
- Serviceability, warranty terms and local support.
- Environmental rating for the site’s weather and dust conditions.
- Power sharing capability within and between cabinets.
- Payment and access features appropriate to the user group.
Cost drivers
| Cost driver | Why it matters | How to manage it |
|---|---|---|
| Utility service and transformer | Capacity upgrades can dominate cost and schedule | Request early, use load management |
| Trenching and civil work | Distance between service and chargers drives cost | Locate equipment close to the source |
| Switchgear and distribution | Higher power requires larger equipment | Phase with spare capacity |
| Charger hardware | Power level and quantity set price | Match power to dwell time |
| Software and operations | Network fees and maintenance recur | Compare lifecycle cost, not purchase price |
| Incentives and rates | Programs can offset capital and operating cost | Check current offerings early |
For help placing charging within a larger budget, see our article on how to estimate MEP engineering costs.
9. Best Practices, Mistakes and Commissioning
Best practices
- Begin with vehicle duty cycles, and write them down in the basis of design.
- Install conduit and panel capacity for the end state, even if the chargers arrive in phases.
- Choose standards-based equipment with a clear upgrade path.
- Use load management to match the service to the real need.
- Engage the utility early, and plan for lead times.
- Coordinate with architects, civil engineers and fire authorities from the start, and align charging with the energy goals described in our net zero building MEP design guide.
Common mistakes
- Counting chargers and ignoring energy and dwell time.
- Forgetting the 125 percent continuous load factor in feeder and breaker sizing.
- Underestimating the distance from the service to the parking area.
- Skipping accessible space and route requirements until late in design.
- Selecting proprietary systems that cannot work with other vendors.
- Not planning for charger failures, leaving vehicles without a spare port.
Testing and commissioning
Commissioning confirms that the system behaves as designed. Tests include inspection against the drawings, protective device settings, charger output and safety functions, communications, load management response, payment and access features, and operator training. Good documentation lets the owner maintain the system for years.
Also Read: Electrical Engineering Services for Future Load Expansion
- Design from vehicle energy and dwell time, then size chargers and service.
- Load management can serve many ports from a smaller service.
- NEC Article 625, CALGreen and accessibility rules shape every project.
- Utility timelines often control the schedule, so start early.
- Build the backbone for the end state and add chargers in phases.
- Commission the whole system, including software and load management.
10. Where Budlong Delivers This
Budlong designs from offices in Glendale, downtown Los Angeles, Camarillo and Fremont, and serves Los Angeles, Ventura, Orange, San Bernardino, Riverside and Santa Barbara counties. Our teams combine utility knowledge with electrical engineering, sustainability and technology expertise, supported by a long MEP portfolio.
11. Related Reading
12. Frequently Asked Questions
How much electrical capacity does a commercial EV charging site need?
It depends on the number of vehicles, the energy each needs per day, the hours available to charge and the charger power level. A fleet that needs its daily energy over a long overnight window can often be served with far less capacity than the sum of all charger ratings, provided load management is designed in. A load study with utility input gives the real figure.
What is the difference between Level 2 and DC fast charging?
Level 2 chargers deliver alternating current to the vehicle’s onboard charger at power levels commonly up to about 19 kilowatts, which suits long dwell times. DC fast chargers convert power in the station and deliver direct current to the battery at much higher levels, which suits short dwell times, but they need larger service equipment and more space.
What does the NEC require for EV charging equipment?
NEC Article 625 covers electric vehicle power transfer systems, including listing of equipment, branch circuit and overcurrent protection sized for continuous load, disconnecting means, and installation location requirements. It also recognizes energy management systems that limit load. Local amendments and the adopted edition control the exact rules for your project.
Does California require EV charging in new commercial buildings?
California’s green building standards code sets requirements for EV capable spaces and installed charging in new nonresidential construction, and the building code adds accessibility requirements for charging spaces. The percentages and details depend on the adopted edition and the occupancy, so confirm them with the local authority having jurisdiction early in design.
What is load management and why use it?
Load management software or controls limit the power delivered across a group of chargers so that the total stays within a set capacity. It lets a site install more charging ports on the same service, shifts charging to lower cost hours and avoids peak demand charges, while still delivering the energy each vehicle needs by its departure time.
How long does utility coordination take?
Utility coordination can take many months, and large services may involve transformer or distribution upgrades with long lead times. Start the conversation during schematic design with an estimated load, ask for the utility’s application process and any make-ready or incentive programs, and treat the utility schedule as a critical path item.
Should a fleet install more chargers than vehicles?
Not necessarily. A one to one ratio is common for depots where each vehicle parks in a fixed stall overnight, while shared chargers can work where vehicles rotate. The right ratio depends on route schedules, dwell time, charger power and the need for spare capacity so that a failed charger does not strand a vehicle.
Can solar and battery storage reduce charging costs?
They can. Solar generation offsets daytime energy, and battery storage can supply part of the charging load during peak periods, reducing demand charges and sometimes the size of the utility service. The benefit depends on the vehicle schedule, the rate structure and available space, so it should be modeled before it is committed to the design.
What is included in commissioning an EV charging system?
Commissioning typically includes inspection of installed equipment against the design, verification of protective device settings, testing of each charger’s output and safety functions, confirming network communication and load management behavior, checking payment and access features, and documenting results and training for operators.
