EV Charger Throttled-Current Schedule (NEC 625.42)
What each car actually gets when an EV energy management system throttles.
Example
You enter
- EVEMS aggregate limit (A) 100
- Per-charger maximum (A) 40
- Active chargers (drawing at once) 4
You get
- Throttled current per charger 25
- Chargers that can run at full rate 2
Checked against published worked examples from: NEC 2023 Article 625 (625.42(A) EVEMS).
Details, formula, and sources
Scopethrottled = min(charger_max, aggregate_limit / active_chargers). Four 40 A chargers on a 100 A EVEMS budget do not each get 40 A - the system throttles all four to 25 A, and only two could run at full rate at once. Drop to two active and both get their full 40 A. Predicts charge times and explains why the last car in slows the rest. A planning aid, not the EVEMS configuration.
Formula or tablethrottled_a = min(charger_max_a, aggregate_limit_a / active_chargers); full_rate_count = floor(aggregate_limit_a / charger_max_a); all_full = active_chargers x charger_max_a <= aggregate_limit_a.
Source and editionNEC 2023 (NFPA 70). Article 625 (625.42(A) energy management systems) per-charger current sharing.
Free accessFree read-only access at nfpa.org/freeaccess.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesaggregate_limit_a, charger_max_a, active_chargers, throttled_a, full_rate_count
- Equal share the EVEMS shares the aggregate limit equally among active chargers, never above a charger's maximum; priority/round-robin schemes differNEC 2023 625.42(A)
- Hardware enforced a listed EVEMS whose limit is enforced in hardware is what permits the sharingNEC 2023 625.42(A); the AHJ governs