Published: June 2026 Technical Level: Advanced Category: Power Systems Design
The electrical design of electric vehicle supply equipment (EVSE) installations is governed by NEC Article 625, which establishes requirements for the wiring methods, circuit sizing, disconnecting means, and grounding of EV charging equipment. For large commercial and industrial EVSE installations, Article 625 interacts with Articles 220 (load calculation), 215 (feeders), 230 (services), 250 (grounding), and 705 (interactive systems for bidirectional V2G equipment) in ways that require careful coordination to produce a code-compliant design. This paper develops the NEC Article 625 design requirements in the context of large commercial EVSE installations — workplace charging, retail charging, and fleet charging depots — and addresses the circuit sizing, panelboard and switchboard loading, conductor sizing, and equipment selection decisions that determine the compliance and performance of the installation. The load management provisions of NEC 625.42 and their interaction with the Article 220 demand calculation are addressed in detail, as these provisions are the principal mechanism by which large EVSE installations avoid impractically large service upgrades.
NEC 625.2 defines electric vehicle supply equipment as "the conductors, including the ungrounded, grounded, and equipment grounding conductors, the electric vehicle connectors, attachment plugs, and all other fittings, devices, power outlets, or apparatus installed specifically for the purpose of delivering energy from the premises wiring to the electric vehicle." NEC 625.40 requires that an EVSE circuit have an ampacity of not less than 125 percent of the EVSE's nameplate current — the continuous load factor required by NEC 210.19(A)(1) for branch circuits supplying continuous loads.
For a hardwired Level 2 EVSE rated 48 A at 240 V single-phase, the branch circuit conductor must be sized for at least 48 × 1.25 = 60 A, and the overcurrent protective device must be rated for at least 60 A. Using 6 AWG THWN-2 copper conductors (75 A allowable ampacity from NEC Table 310.16) in a 1-inch conduit with a 60 A circuit breaker satisfies both requirements: the 60 A breaker protects the circuit at 125 percent of the EVSE's rated current, and the 75 A conductor has adequate ampacity margin above the 60 A breaker rating.
NEC 625.42 permits electric vehicle charging loads to be calculated using a demand factor when an automatic load management system is employed. Specifically, 625.42(B) allows the feeder and service load to be calculated based on the maximum load permitted by the load management system rather than the sum of the EVSE nameplate ratings, provided the management system limits the total load to the calculated value and cannot be overridden. This provision is critical for large installations: without it, a 100-port Level 2 installation would require a service sized for 100 × 60 A = 6,000 A at 240 V single-phase, which is impractical. With an automatic load management system that limits the aggregate demand to 300 A, the service need only be sized for 300 A.
The load management system must be listed for the purpose, must automatically reduce the load when a new vehicle connects if the aggregate would exceed the managed limit, and must be connected to the service entrance or feeder by a means that prevents the total load from exceeding the managed limit under any operating condition. The engineer must document the managed load calculation in the design package and verify with the AHJ that the load management credit under 625.42(B) is acceptable before finalizing the service and feeder sizing.
The standard service and feeder sizing procedure for an EVSE installation begins with the Article 220 load calculation incorporating the Article 625.42(B) managed load credit, adds the EVSE load to the building's existing loads, and sizes the service and feeder conductors and overcurrent devices for the total calculated load. The calculation for a workplace charging installation with 50 Level 2 ports (7.2 kW each at 240 V single-phase) and an automatic load management system limiting aggregate demand to 60 kW proceeds as follows.
The managed aggregate current at 240 V single-phase is A. The existing building peak demand is 400 A at 480Y/277 V three-phase (from the 15-minute demand data). Converting to a common base for service sizing: the EV load, which is 240 V single-phase, is typically served through a step-down transformer from the 480 V service. The step-down transformer must be sized for the EVSE managed load plus 25 percent continuous load margin: 60 kW × 1.25 = 75 kW, or approximately 80 kVA to the next standard transformer size. The transformer primary current at 480 V three-phase is A, and the primary feeder must be sized for 90.2 × 1.25 = 113 A (continuous load factor) — 2/0 AWG THWN-2 copper is adequate at 150 A allowable ampacity from Table 310.16.
NEC 625.43 requires that each EVSE have a disconnecting means within sight of the EVSE and within the EVSE enclosure or adjacent to it. For hardwired EVSE, the disconnecting means may be the branch circuit breaker in the panelboard if the panelboard is within sight, or a local fusible disconnect or circuit breaker mounted on the wall adjacent to the EVSE if the panelboard is not within sight. For DC fast chargers with input currents above 100 A, a bolted-pressure contact fusible disconnect or a molded-case circuit breaker rated for the short-circuit available at the DCFC input terminals must be provided within sight of the DCFC.
NEC 625.54 requires that outdoor EVSE be listed for wet locations and be located such that the vehicle connector and cable are not subject to vehicular damage when the vehicle is in a charging position. For parking structure installations, this requirement drives the mounting height (minimum 18 inches above the finished floor for the connector) and the bollard or pedestal placement relative to parking stalls.
NEC 625.54 requires that all non-current-carrying metal parts of the EVSE be grounded per Article 250. The equipment grounding conductor must be run with the circuit conductors from the EVSE panel or overcurrent device to the EVSE, and must be sized per NEC Table 250.122 based on the rating of the overcurrent device protecting the circuit. For a 60 A circuit breaker, the minimum equipment grounding conductor is 10 AWG copper. For EVSE with automatic ground fault circuit interrupter (GFCI) protection built into the EVSE (as many listed EVSE provide), the NEC 625.54 GFCI requirement for EVSE in all locations except dedicated dwelling unit garages is satisfied by the EVSE's internal GFCI.
The analysis in this paper connects to several companion studies in this library. Readers concerned with the upstream and downstream engineering will find Electric Vehicle Charging Load Management develops a closely related aspect of the same problem, while Electric Vehicle Charging Infrastructure extends the treatment into an adjacent domain. For the broader methodological context, Electric Vehicle Charging Infrastructure Deployment provides complementary depth.
The electrical design of EVSE installations under NEC Article 625 requires coordinating that article with Articles 220, 215, 230, 250, and, for bidirectional V2G equipment, 705, and the central conclusion of this paper is that the treatment of EVSE as a continuous load — requiring conductors and overcurrent devices sized to 125 percent of the continuous rating — is the foundational requirement from which the service and feeder sizing follow. The analysis developed here shows that for large installations the Article 625 load-management provisions are what make the design tractable, because sizing every feeder to the sum of full continuous charger ratings produces an uneconomical and often infeasible service. For the practicing engineer, the operative discipline is to apply the continuous-load multiplier correctly, establish the disconnecting means and equipment location per the article's requirements, and verify grounding and bonding across the coupled NEC articles, while using the load-management provisions to reconcile the installation's nameplate capacity with the available service. The takeaway is that Article 625 compliance is an exercise in coordinating multiple interacting code articles around the continuous-load basis.
[1] NFPA 70, National Electrical Code, Articles 210, 215, 220, 250, 625, 2023 edition, NFPA, 2023.
[2] SAE International, SAE J1772: EV Conductive Charge Coupler, SAE, 2017.
[3] IEEE Standard 1547-2018, Standard for Interconnection and Interoperability of Distributed Energy Resources, IEEE, 2018.
[4] UL 2594, Standard for Electric Vehicle Supply Equipment, UL, 2021.
[5] EPRI, Electric Vehicle Charging Infrastructure — Planning and Design Guide, EPRI 3002019900, 2022.
[6] CharIN e.V., Combined Charging System (CCS) Specification, CharIN, 2022.
[7] NFPA 70, National Electrical Code Handbook, NFPA, 2023.
[8] Chademo Association, CHAdeMO Protocol Specification, Chademo, 2022.