When to use: Sizing the service or feeder impact of EV charging equipment. Per NEC 625.42 EVSE is a continuous load, so conductors and overcurrent protection are sized at 125% of the rated current. An energy management system or load calculation may permit a diversity / demand factor below 100% to reduce the connected load. Use this to assess whether an existing service can absorb the new EVSE load.
This calculator determines the electrical demand load of electric vehicle supply equipment (EVSE) installations per NEC Article 625, sizing the service or feeder conductor and overcurrent protection for single- and three-phase systems. Engineers use it to assess whether an existing service can absorb EV charging load and to specify the required current for new EVSE feeders.
EVSE is classified as a continuous load under NEC 625.42, meaning conductors and overcurrent protection devices must be rated at 125% of the calculated load. The connected load is the sum of all charger ratings: P_connected = N_chargers × kW_per_charger. An energy management system (EMS) or demand factor reduces this to the design demand load: P_demand = P_connected × (diversity/100).
Demand current is derived from the demand load using Ohm's law. For single-phase systems: I = P_demand × 1000 / V. For three-phase: I = P_demand × 1000 / (V × √3). Because EVSE is continuous, the conductor and OCPD sizing current = I × 1.25 (NEC 625.42).
Service impact is assessed by adding the EVSE demand load to the existing service load. If the total exceeds the service rating, either a service upgrade, load management, or a demand-limiting EMS is required. NEC 625.42(A) permits demand factors when a Listed EMS is installed to limit total EVSE load below the calculated maximum.
NEC Article 625 (Electric Vehicle Power Transfer System) is the primary code for EVSE installations. Section 625.42 addresses load calculations and specifies the 125% continuous load multiplier. Section 625.40 requires each EVSE to be supplied by an individual branch circuit, and 625.44 addresses the EMS exception to demand calculation.
NEC Article 220 (Branch-Circuit, Feeder, and Service Load Calculations) governs the service and feeder demand calculations. The EVSE load calculated under Article 625 is added to the total service demand per NEC 220.87 or the standard Article 220 methods.
IEC 61851 (international) and SAE J1772 (North American) define the physical and electrical interfaces for Level 1 and Level 2 AC charging. CHAdeMO and CCS (Combined Charging System) protocols govern DC fast charging. OCPP (Open Charge Point Protocol) is the communications standard for managed charging and smart EMS systems.
Level 1 charging (120V, 12A) provides 1.4 kW per outlet and is typically suitable only for overnight residential charging of plug-in hybrids. Level 2 charging (240V, 16–80A) delivers 3.3–19.2 kW and is the standard for commercial and workplace installations. DC fast charging (DCFC) operates at 50–350 kW per port and requires a dedicated 3-phase service with demand management.
Diversity factor selection is critical for multi-port stations. Without EMS, all chargers must be assumed to draw simultaneously (100% diversity). With a Listed EMS limiting total site load, diversity factors of 50–70% are common in fleet and workplace charging deployments, significantly reducing the required service capacity.
Future load growth is a critical planning consideration. The DOE projects EV adoption will require 3–4× current charging infrastructure by 2030. Conduit and service capacity should be sized for future expansion even if chargers are not immediately installed — rough-in conduit costs far less than future trenching and service upgrades.
Enter the number of EVSE chargers and the power per charger (kW). For Level 2 chargers, common ratings are 7.2 kW (32A/240V), 11.5 kW (48A/240V), and 19.2 kW (80A/240V). For DCFC, use 50, 100, 150, or 350 kW per port.
Set the diversity factor to 100% if no EMS is installed. If a Listed EMS limits total EVSE load, consult your EMS vendor for the permitted demand factor and enter it here. Enter the existing service load to assess total service demand.
Select the service voltage (208, 240, or 480V) and phase configuration. Review the Results panel for demand current and the continuous sizing current (×1.25 per NEC 625.42). The total service load shows whether a service upgrade is needed.
NEC 625.42 classifies EVSE as a continuous load, requiring conductors and overcurrent protection to be rated at 125% of the calculated EVSE load current. This is the same treatment as other continuous loads under NEC 210.20 and 215.3. So a 48A Level 2 charger requires a 60A circuit (48 × 1.25 = 60A), typically served by a 60A breaker and 4 AWG copper conductors.
Yes, but only if a Listed energy management system (EMS) is installed per NEC 625.42(A). The EMS must be specifically listed for this purpose and must actively limit total EVSE load below the connected maximum. Without an EMS, all chargers must be assumed to draw simultaneously at full rated current, requiring 100% diversity in the load calculation.
Level 1 uses a standard 120V/15A outlet (1.4 kW, limited to PHEV and overnight use). Level 2 uses 240V with 16–80A circuits (3.3–19.2 kW, suitable for most EVs and fleet applications). DCFC bypasses the on-board charger and delivers 50–350 kW directly to the battery, requiring 3-phase power and capable of charging a 75 kWh EV in 20–45 minutes.
At 11.5 kW (48A, 240V, 1-phase) per charger with 100% diversity: connected load = 10 × 48A = 480A demand current. Continuous sizing = 480 × 1.25 = 600A. This typically requires a dedicated 3-phase 480V feeder with a step-down transformer to 240V, or a 600A 240V single-phase service — both are expensive. With a Listed EMS at 50% diversity: demand = 240A × 1.25 = 300A sizing, a much more practical installation.
Yes. The EVSE demand load (after diversity and the 1.25 continuous multiplier) is added to all other building loads when performing the service entrance load calculation under NEC Article 220. If the total exceeds the existing service rating, NEC 220.87 allows use of measured demand data to verify the service is adequate, potentially avoiding a full service upgrade for existing commercial buildings.
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