EV Charging
EV charging is now standard on every commercial project. NEC 625 governs. Demand factors for EVSE differ from general receptacles. Energy Management Systems (EVEMS) reduce service-size requirements.
NEC Article 625 — EV Charging Equipment
EV charging is now standard on every commercial project. NEC 625 governs it. Demand factors differ from general receptacles. EVEMS (Energy Management Systems) reduce service-size requirements through load shedding.
| Charging Level | Voltage | Current | Power | Use |
|---|---|---|---|---|
| Level 1 | 120V 1φ | 12-16 A | 1.4-1.9 kW | Residential, slow trickle. ~ 4-6 mi/hr added range. |
| Level 2 | 208V or 240V 1φ; some 480V 3φ commercial | 16-80 A | 3.3-19.2 kW | Standard residential + most commercial. ~ 10-60 mi/hr. |
| DC Fast Charging (DCFC) | 480V 3φ in; DC out | varies | 50-350+ kW | Highway corridor, fleet refueling. ~ 100-400 mi/hr. |
| "Megawatt Charging" (MCS) | 1000V+ DC | 3000+ A | 1-3.75 MW | Heavy duty trucks, buses (emerging) |
EV Charging Is Always Continuous
Per NEC 625.41, EV charging is classified as a continuous load regardless of duration. So 125% multiplier applies to wire and breaker. This is true even for a 30-min DCFC session.
Branch circuit sizing
OCPD ≥ 1.25 × (EVSE rated input current)
Example: 40A EVSE → 50 A breaker minimum, with #6 Cu THWN-2.
EVEMS — Energy Management Systems (NEC 625.42)
NEC 625.42 allows demand factor reduction via Energy Management Systems (EVEMS). Without EVEMS, sum of all EVSE branches is treated as 100% continuous. With EVEMS, the system can dynamically limit total simultaneous charging power → service size much smaller.
| Approach | Demand calculation | Service size impact |
|---|---|---|
| No EVEMS — full simultaneous | 100% × N stations × max kW each × 1.25 continuous | Largest. 50 stations × 7.2 kW = 360 kW + 1.25 = 450 kW |
| EVEMS — dynamic load sharing | Configured maximum kW (sum < service capacity) | Smallest. EVEMS limits total to e.g. 100 kW shared across all stations |
| EVEMS — load-shedding hierarchical | EVEMS sheds EV load when other building loads peak | Allows EV charging on tight existing services |
DCFC — Special Considerations
| Aspect | Detail |
|---|---|
| Power level | 50, 100, 150, 175, 250, 350 kW per stall typical. 480V 3φ input. |
| Service requirement | A 4-stall 350 kW DCFC site = 1.4 MW peak. Often requires utility upgrade. |
| Demand factor | Per NEC 625.42(B), allowable diversity for > 1 station based on charging session statistics. Real-world: rarely all stalls full at full power. |
| Harmonic content | DCFC is a large rectifier — significant harmonics. Often passive or active filter required at site to meet IEEE 519. |
| Fault current | Service often upgrades fault current at site. Equipment AIC must accommodate. |
| Coordination with utility | For sites > 250 kW, often requires custom rate + demand charge structure. Utility approval lead time. |
Worked Example 1 — Atlas DC1 EV Charging Station
Example 01 · Atlas DC1 spineAtlas DC1 office building parking — 4 Level 2 + 1 DCFC for fleet
Equipment list
| Item | Qty | Spec | Branch |
|---|---|---|---|
| Level 2 EVSE — staff parking | 4 | 208V 1φ, 40 A continuous | 50 A breaker, #6 Cu in 1" EMT |
| DCFC — fleet vehicles | 1 | 480V 3φ, 75 kW (90 A input) | 125 A breaker, 1/0 Cu in 1.5" EMT |
Service impact analysis
- Without EVEMS — full simultaneous load:4 × (208 × 40 × 1.25) + 75 × 1.25 / 0.95 = 41.6 + 99 = 140 kW peak
- With EVEMS: Shed Level 2 stations during DCFC session. Max total = 75 kW DCFC OR 4 × 8.3 kW = 33 kW Level 2 = max 75 kW peak (one or other).
- Atlas DC1 chose EVEMS: Existing service has limited EV capacity allocation. EVEMS reduces peak from 140 to 75 kW = 50% smaller transformer needed for EV.
- Branch from 480V SWGR-A: Dedicated EV panel fed from 480V SWGR. 200 A branch CB, 4/0 Cu sub-feeder to EV panel.
Worked Example 2 — Highway Corridor DCFC Site
Example 02 · Alternate contextStandalone highway DCFC site — 4 stalls × 350 kW each
- Site demand: 4 × 350 kW = 1.4 MW peak. With 1.25 continuous = 1.75 MW.
- Service: Customer-owned 12.47 kV utility service with on-site step-down. 2 MVA pad-mount transformer at 480V.
- Switchgear: 480V switchgear with 4 × 600 A feeder breakers (one per DCFC stall).
- EVEMS: Often NOT used for highway DCFC because customers expect full power on demand. Service sized for full simultaneous use.
- Harmonics: 4 × 350 kW DCFC = significant 5th and 7th harmonic injection. Active filter required to meet IEEE 519 at PCC.
- Utility coordination: 12+ months lead time. Site-specific demand rate negotiation.
Drill — Quick Self-Check
Work each problem mentally; reveal to check. Goal: reflex, not deliberation.
Drill 1 · Continuous classification
EV charging is what kind of load per NEC 625.41?
Always continuous
Apply 125% to wire AND breaker.
Drill 2 · Level 2 voltage
Standard Level 2 EV charging voltage?
208V or 240V
1φ; 16-80 A.
Drill 3 · DCFC voltage
DC Fast Charging input?
480V 3φ
DC out to vehicle.
Drill 4 · EVEMS purpose
What does EVEMS reduce?
Service size required
By limiting simultaneous EV charging via load shedding.
Drill 5 · EVSE vs EV
Where is the actual battery charger?
In the car, not the wall unit (EVSE)
EVSE just provides regulated power.
If You See THIS, Think THAT
| If you see… | Think / use… |
|---|---|
| NEC 625 | EV charging equipment installation rules. |
| "Level 1" charging | 120V residential. 1.4-1.9 kW. Slow. |
| "Level 2" charging | 208V or 240V. 3.3-19.2 kW. Standard residential + most commercial. |
| "DCFC" or "Level 3" | 480V 3φ in, DC out. 50-350+ kW. Highway corridor. |
| "EVSE" | Electric Vehicle Supply Equipment. The "charger." (Actual battery charger is in the car.) |
| "EVEMS" | Energy Management System per NEC 625.42. Limits total simultaneous EV charging power. Allows smaller services. |
| EV charging classified as | ALWAYS continuous load. 125% rule applies. |
| "4-stall 350 kW DCFC site" | 1.4 MW peak. Customer-owned MV service required typically. |
| NEMA 14-50 outlet | Common Level 2 receptacle (50 A 240V). |
| "Anti-islanding for V2G" | Vehicle-to-Grid bidirectional charging. Inverter standards apply. |
| "OCPP" | Open Charge Point Protocol. Industry standard for EVSE communication. |