Expert presenters Dave Wernli and Kamil Yenice answer audience questions from an April webcast on EV charging.
In the webcast Critical power: Designing for EV charging stations, presenters Dave Wernli, PE and Kamil Yenice, PE spent an hour discussing design considerations for electric vehicle service equipment (EVSE). The presentation covered space and load considerations, challenges for these designs and necessary codes and standards.
Audience questions from the end of the webcast are addressed below.
What are the primary challenges you run into on the EV infrastructure side?
Dave Wernli: The biggest challenge we run into is the timeline, generally with procurement of the electrical service equipment and utility coordination and energization.
Supposing there is no load management, please clarify how the service can be sized at 100%, given that the EV is considered a continuous load.
Dave Wernli: 2023 NEC 625.41: Electric Vehicle Charging System requires an overcurrent protection device for feeders and branch circuits to be sized for 125%. The service main remains governed by NEC 220 Branch-Circuit, Feeder and Service Calculations and NEC 230: Services.
Would the Emergency Disconnect apply to Class 1 Chargers as well?
Kamil Yenice: Assuming this question relates to the upcoming code changes, the proposed revision does not reference any specific EV charger types (Level 1, Level 2 or Level 3). Instead, it applies broadly to all levels of EV chargers.
With the upcoming changes to NEC Article 625: Electric Vehicle Charging System, would emergency disconnect switches be required regardless of whether or not the installation requires an equipment disconnect?
Kamil Yenice: According to the upcoming code revisions, electrical vehicle service equipment (EVSE) and wireless power transfer equipment must be provided with one or more disconnecting means as required by NEC 625.43(D) and 625.43(E). In accordance with NEC 625.43(E)(2), the disconnecting means required under 625.43(D) is permitted to serve as the emergency disconnect, provided it complies with all the requirements of 625.43(E).
Could a company use the vehicle/charger to control the power draw at a certain time period?
Dave Wernli: Yes, however, using the vehicle alone for demand control is likely done by each individual vehicle, and unified energy management is not typically feasible in that case. Chargers can be set to limit their maximum output and, as discussed, dynamic demand management would require centralized or ad-hoc communication between chargers.
Is there any precedence to design park spaces to comply with the Americans with Disabilities Act (ADA) access without labeling them as handicapped due to parking limitations for other customers?
Dave Wernli: Yes. Refer to the International Building Code 1107: Dwelling Units and Sleeping Units guidelines and access board recommendations. Accessible spaces do not need to be restricted ADA spaces.
For the emergency disconnect device, do you believe an integral disconnect meets the new NEC 2026 requirements?
Kamil Yenice: No, a disconnect switch integral to the EVSE does not meet the location requirements outlined in NEC 625.43(E)(1). The code requires that the emergency disconnect must be installed in a readily accessible location, situated not less than 20 feet and not more than 100 feet from the equipment and within sight of the equipment. An integral disconnect does not satisfy these distance and visibility requirements.
Is it common to see NEC-required ground fault interrupters (GFI) and disconnects integral to charger stations (included by the manufacturer)?
Dave Wernli: Yes. Many Level 1 and 2 chargers have GFI capabilities integrated.
Is the emergency stop a remote shunt trip?
Dave Wernli: Remote shunt trip is one viable means. Some commercially available chargers have internal mechanisms as well.
What do they call the robot arm large bus and truck chargers? Maybe the “Level” nomenclature no longer applies? Does the NEC cover these?
Dave Wernli: Chargers with dispensing rates up to 1MW are available with the ‘standard’ configuration of a removable plug and wire. Both NEC 625.1 and NEC 626.1 describe the equipment to which the rest of each article applies.
Do charge times increase by implementing demand management?
Dave Wernli: Generally, yes. When constrained, the lower delivery rate will extend the charging time.
Any thoughts on a demand management system cost?
Dave Wernli and Kamil Yenice: The cost of a demand management system for EV charging stations can vary significantly depending on several factors, including the scale of the installation, the complexity of the system and the specific features needed.
Since EV chargers are continuous loads, when sizing EV panelboards, do you have to multiply the total EV load by 125% and size the main breaker accordingly?
Kamil Yenice: Yes, according to the NEC, Electric Vehicle (EV) chargers are considered continuous loads. Per NEC Article 625 and NEC 210.20(A), when sizing overcurrent protection and panelboards for continuous loads, you must size the equipment for 125% of the continuous load.
Which authority having jurisdiction (AHJ) should be consulted? State electrical inspector, building codes, fire department, power company, etc.?
Dave Wernli: Generally speaking, the permit office issuing building and electrical permits, and the zoning office should be contacted. Utility outreach should also occur prior to submission of the load letter or new service request.
Must all chargers be counted at 125% of full load amperage (FLA) for load calcs? Are there any load demand factors? For example, if you have 20 ranges in an apartment building, the NEC doesn’t require 125% FLA of all 20 units.
Dave Wernli: Each branch circuit must be calculated at 125% of the equipment’s maximum load. Demand (Load) management may be used in accordance with NEC 750: Energy Management Systems. Services should be sized per NEC 220 and 230, among other requirements.
Level 3 EV chargers have a very low short circuit rating (10kA) and utility input is always above 42kA. How is this being addressed in the design?
Dave Wernli: Many manufacturers offer EVSE with short-circuit current ratings up to (and possibly exceeding) 65kA. Available fault current exceeds your equipment rating; external means to reduce the available current would be required to protect the equipment. Traditionall,y this is done by adding impedance in the system.
Is photovoltaic (PV) solar an option for additional power?
Dave Wernli: Absolutely, solar PV is a great means to offset demand. Combined with an energy management system, chargers can be dynamically controlled to maintain a maximum draw from the grid and maximizing solar energy use.
What is the solution if the available fault current on the terminal of a charger is higher than the short-circuit current rating of a charger?
Dave Wernli: Where available fault current exceeds your equipment rating, external means to reduce the available current would be required to protect the equipment; traditionally by adding impedance in the system.
Is the ‘accessible EV charging use last’ signage/procedure a common practice? Have there been any challenges with this (in terms of use) or with AHJ acceptability?
Dave Wernli: AHJs will always vary and can form their own opinion, but the ‘use last’ signage is proposed by the US Access Board’s “Design Recommendations for Accessible Electric Vehicle Charging Stations”, which has aided in discussions with AHJs.
Can you please expand on fire department requirements? Article 12 of the International Fire Code (IFC) appears to apply to stationary battery energy storage systems and does not contain additional requirements for EVs. Are there IFC or fire department requirements that are common to EV charging facilities?
Dave Wernli: Your assessment aligns with the presenters’ interpretation. However, individual AHJs may (and have) proposed additional protections for EV chargers located in parking garages. I am not aware of any national standard requiring special fire protection treatment for EVSE.
Can you expand on the emergency management systems (EMS) in NEC 750? Is this an electrically operated circuit breaker, current differential relay or something else?
Dave Wernli: The EMS can be a separate system, microgrid control system or on-board the chargers (varies greatly by project needs and equipment selected). The basic structure is a means to monitor the current draw of each charger, a controller that aggregates this demand and a controller output to direct charger(s) to reduce their output to maintain compliance with the ceiling. There are numerous means this structure can be designed with hardware.
Can you expand on electric vehicle charging station (EVCS) design levels, taking into consideration how the electrical consumption integrity, safety and protection into the scope and scheme of design?
Kamil Yenice: Electrical consumption, system integrity, safety and protection are integral to all levels of EVCS design and are addressed through a combination of engineering best practices, code compliance and system planning. At different design levels, these factors are incorporated as follows:
- Electrical consumption: Load calculations are performed early in the design process to determine total demand and potential future expansion. Energy management systems or load sharing controls may be integrated to optimize consumption and avoid overloading infrastructure.
- System integrity: The overall design ensures system reliability by selecting components with proven performance and ensuring proper coordination between equipment.
- Safety: Safety is addressed through compliance with applicable standards such as the NEC Article 625, UL listings and local codes. Designs include proper circuit protection, signage, physical barriers and emergency shutoff mechanisms to protect users and maintenance personnel.
- Protection: Overcurrent protection, ground fault protection, surge protection and fault isolation are key aspects of EVCS design. Protective devices are carefully selected and coordinated to minimize the risk of equipment damage or fire while maintaining service continuity.
Can you define the real state proximity to potential proximities to high voltage systems overhead/underground and explain its limits and guard rails?
Kamil Yenice: The NEC and local utility standards establish minimum vertical and horizontal clearance requirements between electrical equipment and overhead (OH) high-voltage lines. Coordination with the local utility is essential prior to excavation to accurately identify underground (UG) cable paths and avoid conflicts. There are also minimum separation requirements between UG high-voltage lines and newly installed EV infrastructure to prevent interference, ensure safety and reduce the risk of accidental contact. Depending on local codes and utility specifications, additional measures such as warning tape, conduit encasement, physical barriers and defined routing plans may be required. Furthermore, codes often regulate how close EV charging infrastructure (EVCS) can be installed to property lines, especially when near public rights-of-way or adjacent buildings.
Does prioritizing take into consideration the different EVCS per specific applications or power demands?
Kamil Yenice: When designing EVCS systems, particularly for Levels 2 and 3 (DC fast chargers), proximity to high-voltage infrastructure is a critical factor for both safety and system performance. Here’s how this is typically addressed:
OH high voltage lines:
- Clearance requirements: NEC and local utility standards dictate minimum vertical and horizontal clearances between any electrical equipment and overhead high-voltage lines.
- Safety zones: No part of the EVCS should fall within restricted approach boundaries, which vary by voltage level (e.g., 4 ft to 10 ft for 15–35 kV lines).
UG high voltage systems:
- Locate before you dig: Coordination with local utilities is required to identify UG cable paths before excavation.
- Separation requirements: There are required minimum separation distances between UG high voltage lines and any newly installed EV infrastructure to prevent interference or accidental contact.
- Protective measures: Barriers or warning tape, conduit encasement and specific routing plans are often required.
Real Estate Boundaries:
- Property line setbacks: Codes often dictate how close EVCS infrastructure can be to property lines, especially when near public rights-of-way or adjacent structures.
- Access and easements: Coordination with property owners or utility companies may be needed if EVCS design crosses into easements or utility corridors.
What are some of the complexities of designing EV chargers in dense urban locations?
Dave Wernli: The biggest challenge in dense urban locations is likely the additional space requirements of the large service equipment, chargers themselves and vehicle access needs. Traditional means of saving space, such as angled stalls, may preclude some vehicles from effectively using the chargers.
How do you work around utilities that won’t talk to you until your client has paid design fees and you have submitted final electrical loads?
Dave Wernli: This is no different from other projects. Ask politely for additional information or carry the known risk forward until they will communicate.
I understand the consideration of continuous charging at 125% of the rated current, but I didn’t understand what the demand factors are for these chargers.
Dave Wernli: For the demand management graph, the demand factor is applied to the chargers to limit the overall system consumption. It’s both variable by time and by site, so that it can be set by the engineer and operator.
The charging time is important to most people. Do we use input amps to calculate the charging time? How’s charging power measured? Does the charging rate slow slower with time?
Dave Wernli: Charging time is highly variable and is impacted directly by vehicle battery architecture, charge curve, current state of charge and battery temperature. Most EVs will slow their charge rates as they charge past 80% state-of-charge. The general calculation is energy needed in kWh divided by the delivery speed in kW.
Are there any “best practices” or industry standards regarding the application of harmonic mitigation as it relates to EV power distribution?
Dave Wernli: Generally, commercial EVSE should already be compliant with IEEE 519: Standard for Harmonic Control in Electric Power Systems. Additional harmonic mitigation may be appropriate based on combined harmonic profile of the system. The only way to confirm would be to run a simulation or analysis of the site with your program of choice.
Is the accessibility requirement verified by the architect or the engineer?
Dave Wernli: This is typically the responsibility of the architect or civil engineer. As always, coordination of scope at the project outset will guide your team for your specific site.
Could installing EVSE units with power-sharing capability allow for more units to be installed for the same amount of load, qualifying it to meet the quantity requirements?
Kamil Yenice: Yes, installing EVSE units with power or load sharing capability can be a valid approach to meet the quantity requirements, provided the system is designed to ensure that all installed units are capable of delivering the necessary charging service within the expected usage patterns. Power sharing allows more chargers to be installed within a limited electrical capacity by dynamically allocating available power based on demand. However, it’s important to verify that the proposed configuration meets the performance criteria and user expectations outlined in the project or regulatory requirements.
What is the typical kW load for a Level 3 EV charger?
Kamil Yenice: The typical kW load for a Level 3 EV charger—also known as DC fast chargers (DCFC)—varies widely depending on the model and intended application, but generally falls within the following ranges:
- Low-Power DCFC: Ranges from 24–50 kW and is used for light commercial, small fleets and urban areas.
- Mid-Power DCFC: Ranges from 75–150 kW and is used for public charging and highway corridors.
- High-Power DCFC: Ranges from 150–350+ kW and is used for highways, transit hubs and heavy-duty EVs.
If a level 2 charger is 40A, is the current draw 40A or is it usually 80% of that? Is EV considered a continuous load?
Dave Wernli: That will vary, but in this instance, we’re referring to the rated input current. As always, check the cut sheets for your specific equipment.
Does adding a fast charger system introduce a problematic level of harmonics to a light commercial type facility (office space, school, etc.)?
Kamil Yenice: Good question! Yes, adding a DCFC system can introduce problematic levels of harmonics to a light commercial facility, such as an office building or school, depending on several key factors:
- Charger size relative to facility load: Light commercial buildings typically have moderate electrical loads—primarily HVAC, lighting and office equipment. A single DCFC rated between 50 kW and 350 kW can represent a substantial portion of the facility’s total electrical demand, potentially stressing the existing system.
- Charger type and power quality performance: Low-cost or older chargers may lack effective harmonic mitigation features, leading to higher levels of current distortion. Modern chargers with active front-end rectifiers typically perform better in this regard.
- Electrical infrastructure limitations: If the building’s transformer or distribution system is not rated for harmonic-rich loads, it may experience overheating, reduced lifespan or even failure.
Given these risks, a detailed assessment of the electrical system—including harmonic analysis—should be conducted before integrating a DCFC into an existing facility.
I thought that standard water fire suppression was not effective on a lithium-ion fire. Is that not correct anymore?
Kamil Yenice: Water is not reliably effective at extinguishing lithium-ion battery fires. Specialized suppression systems or agents are required. In large installations (like EV charging stations or battery energy storage), high-volume water spray is sometimes used to cool surrounding equipment and prevent fire spread, not necessarily to extinguish the battery itself.
Is oversubscription defined and codified? If so, is it specifically for EV chargers?
Kamil Yenice: Oversubscription, as a design concept, is not currently defined or codified in the NEC or any other major national model codes for EV chargers specifically. However, the concept is recognized and increasingly used in practice, particularly in large-scale EV charging installations and load management systems.
How often is IEEE-519 in specifications? What are the best methods for achieving compliance?
Kamil Yenice: IEEE 519: Standard for Harmonic Control in Electric Power Systems does not specifically address EV charging systems. Instead, it provides general guidelines for controlling harmonic distortion in electrical power systems to ensure power quality and protect equipment. While IEEE 519 doesn’t directly reference EV chargers, any equipment (including EVSE) that contributes to harmonic distortion must comply with the harmonic limits outlined in the standard.
What is the condition that mandates the use of a residual current circuit breaker (RCCB) type A in the EV charging Panel?
Kamil Yenice: The use of an RCCB Type A in an EV charging panel is typically mandated when there is a potential for both AC and DC residual currents. Type A RCCBs are designed to detect both alternating and pulsating DC fault currents, which makes them essential for EV charging systems that include components such as rectifiers, inverters or electronic circuits. These components can generate DC leakage currents, which Type AC RCCBs are unable to detect. Therefore, a RCCB Type A is required to ensure comprehensive protection against electrical faults in systems that may produce DC residual currents.
Is there a clear delineation between a parking lot and a parking garage? Would covered parking require sprinklers? Or a parking lot covered by PV?
Kamil Yenice: The classification of a parking area as a lot or a garage depends on structural and fire code definitions. Covered parking—such as that with PV canopies—does not inherently require sprinklers, but local codes and AHJ interpretations determine final requirements based on enclosure, materials and fire risk.
What equipment is required to implement and install an effective demand management system for EV charging infrastructure?
Kamil Yenice: Equipment requirements can vary by manufacturer and depending on the specific type of energy management strategy being implemented. However, the typical core EMS equipment and devices generally include the following:
- Smart EV chargers.
- EMS/load management controllers.
- Electrical submeters/power meters.
- Current transformers/sensors.
- Load control relays/contactors.
- Panelboards/distribution panels.
- Communications gateway/networking equipment.
- Conduit, cabling and wire management.
In high-density EV charger installations within a parkade, is it acceptable under the NEC to integrate the emergency shutoff function into the EV charger assembly, given that providing individual disconnects for each unit may not be practical or feasible?
Kamil Yenice: Based on the upcoming code revisions, this installation would not be compliant, as the emergency disconnect device must be located no closer than 20 feet and no farther than 100 feet from the equipment, and it must be within sight of the equipment.
Is the availability and reliability of cellular coverage essential for the site to support communication needs for metering and payment processing systems? Are there contingency plans in place if coverage is insufficient?
Kamil Yenice: Yes, the availability and reliability of cellular coverage is essential for sites that rely on metering and payment processing systems, particularly in EV charging stations, self-service kiosks or remote energy metering installations. These systems often depend on real-time communication to process transactions, transmit usage data, perform remote diagnostics and receive updates. Contingency measures may include the use of both cellular and Ethernet or Wi-Fi as backup if coverage is insufficient. In critical infrastructure, a wired internet connection may be preferred or required.
Do we have demand factors for load tabulation in design? Do we simply assume 100%?
Kamil Yenice: There are no demand factors involved. All EVSE loads are considered to be continuous loads. Per NEC Article 625: Electric Vehicle Charging System and NEC 210.20(A): Continuous and Noncontinuous Loads, when sizing overcurrent protection and panelboards for continuous loads, you must size the equipment for 125% of the continuous load.
Are there any special design considerations for bi-directional EV chargers with grid-forming capabilities?
Kamil Yenice: Vehicle-to-Grid integration enables electric vehicles to discharge stored energy back to the grid or facility during periods of high demand. This capability requires bi-directional chargers, compatible vehicle technology and appropriate utility interconnection agreements and regulatory approvals.
With the federal government abolishing EVSE, will the Architectural Barriers Act (ABA) be required? Are there still federal incentives?
Kamil Yenice: To our knowledge, the federal government is not taking any action to abolish EVSE. ABA standards continue to apply to EVSE installations located in state or local government facilities, including office buildings, public parks, municipal parking lots, on-street parking, public rights-of-way and residential housing provided by state or local agencies. For information on available federal incentives, please visit the U.S. Department of Energy’s website.
Has anyone started making adapters?
Dave Wernli: Yes. Many vehicle manufacturers offer OEM adapters, and a number of aftermarket adapters are available for most variations of plug and receptacle.
Are there defined differences between large, commercial EVs and passenger-type EVs?
Kamil Yenice: Yes. While passenger EVs are designed primarily for individual use with a focus on efficiency and comfort, large commercial EVs are engineered to handle heavy loads, long operating hours and specific fleet requirements. The larger size, greater power demand and specialized infrastructure needs make them fundamentally different in both design and operation.
Do we need a specific transformer for EV chargers?
Kamil Yenice: K-rated transformers are well-suited for EV charger applications due to their ability to handle the harmonic-rich loads commonly associated with EVSE. It is recommended to consult with the transformer manufacturer to select the appropriate K-rating based on the specific EVSE load characteristics and the demands placed on the distribution system.
For parking garages, you also need to consider structural issues as EVs’ weight is greater than most internal combustion vehicles.
Kamil Yenice: When planning EV installations in parking garages, it’s important to evaluate the structural capacity of the facility, particularly in older buildings not originally designed for higher vehicle weights. Coordination with a structural engineer is recommended to assess load-bearing limits and ensure compliance with applicable building codes and safety standards.
Is an emergency shunt trip disconnect currently required?
Kamil Yenice: An emergency disconnect switch is not currently required by the NEC. However, as discussed in the webcast, upcoming code revisions will mandate the inclusion of emergency disconnect switches for certain installations.
Is ground fault protection part of the charging station or upstream at the serving panel?
Dave Wernli: This varies by installation and charger. Receptacles for EV chargers are required to have GFCI protection per NEC 625.54.
When looking at generator sizing for back-up, do the charging stations look more like a resistive load or is there a large inrush and/or power factor issues?
Dave Wernli: There is not typically a large inrush for new connections. Chargers typically ramp up the power delivered when first plugged into a vehicle and can typically be modeled as a rectifier with a variable load. Consult the detailed equipment specifications for each charger when preparing for generator backup.
How do you model Level 3 DC fast chargers when sizing backup generators for EV charging sites?
Kamil Yenice: To model Level 3 DC fast chargers for backup generator sizing, begin by calculating the total connected load based on charger ratings (typically 50–350 kW each). Evaluate peak demand scenarios—either full simultaneous use or based on usage forecasts. Since DC fast chargers present non-linear loads, ensure the generator can handle harmonic distortion and rapid load changes. Include all auxiliary loads (e.g., lighting, HVAC), apply a diversity factor if supported by data and add a safety margin. Consult the charger and generator manufacturers for detailed specifications and compatibility.
How does a designer/customer do an economical installation if the utility assessed demand charges, which could be $15 to $20/kW? One charge at 200 kW could establish a monthly demand charge of as much as $4000. You have to do a lot of charges in a month to recover this charge.
Kamil Yenice: You’re absolutely right—demand charges in the range of $15–$20/kW can make high-powered EV charging (like 200 kW fast charging) economically challenging, especially at low utilization rates. Combining load management, utilizing battery energy storage systems, right-sizing and, if possible, rate negotiation is often the best path to economic viability.
Does harmonic interference need to be analyzed after installation?
Kamil Yenice: Harmonic interference typically does not require post-installation analysis unless there are signs of harmonic-related issues within the electrical distribution system. However, if the system includes large non-linear loads, such as DC fast chargers, it may be beneficial to perform a harmonic analysis proactively to ensure power quality and avoid potential problems with sensitive equipment or utility compliance.
How do you reduce the demand load? Is the rate of charge adjustable?
Dave Wernli: To reduce demand, you can set each charger’s maximum output to a given value (assuming it has that capability), or you can utilize a demand management system or EMS. The EMS can be a separate system, a microgrid control system or onboard the chargers. This varies greatly by project needs and equipment selected. The basic structure is a means to monitor the current draw of each charger, a controller that aggregates this demand and a controller output to direct charger(s) to reduce their output to maintain compliance with the ceiling. There are numerous means this structure can be designed with hardware.
What building/fire code provisions govern the installation, operation and maintenance of these battery charging facilities?
Kamil Yenice: The main governing codes include NEC Article 625, the IFC, the International Building Code and applicable NFPA codes. Compliance depends on installation type, scale, location and local code adoption, so early engagement with the local AHJ is essential.
