Grounding Conductor Calculator for Missouri
NEC 2020 grounding conductor math for EV charger installers working in Missouri.
EGC sizing in Missouri follows NEC 2020 Table 250.122, indexed off the upstream OCPD rating, with parallel rules for parallel sets and increased-conductor adjustments under 250.122(B).
Worked example for Missouri
For a 200 A EVSE branch, Table 250.122 calls for a minimum #6 Cu equipment grounding conductor. If you upsize the phase conductors for voltage drop in Missouri's long runs, NEC 250.122(B) requires the EGC to be upsized proportionally.
Code & Utilities
Missouri currently enforces the NEC 2020 edition, adopted in 2022. That includes Article 625 (Electric Vehicle Power Transfer System) requirements: 125% continuous-load sizing on EVSE branch circuits, GFCI protection at outdoor receptacles, and provisions for energy management systems on shared circuits.
Major electric utilities serving Missouri include Ameren Missouri, Evergy Missouri, Empire District Electric. Always verify the applicable tariff and any utility-specific requirements (CT cabinets, metering enclosures, demand limiters) at design time.
Climate & Ampacity
Plan EV feeders against a 95°F ambient in Missouri — the resulting NEC 310.15(B) correction of 0.88× is what trims a #6 THWN-2 down to its true continuous rating. Because the correction is below 0.9, conductors that "look fine" on a 30°C ampacity table will not carry their nameplate current here — always derate explicitly.
Missouri takeaway
On DCFC sites with parallel feeder sets, each parallel raceway needs its own full-size EGC — a detail inspectors in Missouri catch frequently on commercial submittals.