Grounding and Bonding Requirements for EV Chargers in Ohio

Grounding and bonding are foundational safety functions in every EV charging installation, governing how fault current is controlled and how voltage equalization is maintained across conductive components. Ohio installations must satisfy the National Electrical Code (NEC), Ohio's adopted amendments, and the manufacturer specifications of listed EVSE equipment. Failures in either system are a primary cause of shock hazard, equipment damage, and failed inspections across residential, commercial, and fleet charging sites.

Definition and scope

Grounding and bonding are related but distinct electrical safety concepts. Grounding connects non-current-carrying metal parts of an electrical system to the earth, providing a low-impedance path that allows overcurrent protective devices to operate during a fault. Bonding connects conductive parts together to eliminate voltage differences between them, preventing dangerous potential gradients that can cause shock even without a direct earth fault.

For EV chargers in Ohio, both requirements derive from NEC Article 625 (Electric Vehicle Power Transfer System) read in conjunction with NEC Article 250 (Grounding and Bonding), as adopted under the Ohio Building Code. The Ohio Board of Building Standards administers the Ohio Building Code, which incorporates the NEC by reference with state-specific amendments. Local jurisdictions — including Columbus, Cleveland, and Cincinnati — may apply additional inspection requirements but cannot legally adopt codes less stringent than the state minimum.

Scope and limitations of this page: Coverage here applies to Ohio-permitted EV charger installations within the state's building code jurisdiction. Federal installations on military property, tribal lands, and installations regulated exclusively under U.S. Department of Energy facility rules fall outside Ohio's Building Code authority. Utility-side service entrance grounding beyond the meter is governed by each utility's tariff rules, not the Ohio Building Code alone. For broader regulatory context, see the Regulatory Context for Ohio Electrical Systems page.

How it works

Ohio EV charger grounding and bonding systems function through three interdependent components:

1. Equipment Grounding Conductor (EGC): A dedicated conductor run within the same cable or conduit as the circuit conductors, connecting the EVSE enclosure and chassis to the grounding bus in the distribution panel. Under NEC Table 250.122, a 40-ampere branch circuit — the most common Level 2 residential circuit — requires a minimum 10 AWG copper EGC.

2. Grounding Electrode System: The panel's grounding electrode conductor connects the neutral bus and EGC bus to ground rods, metal water pipes, or other electrodes permitted under NEC Article 250 Part III. Ohio inspectors verify that the existing electrode system is compliant before approving new EV circuit permits. Adding an EV circuit does not automatically require a new electrode, but deteriorated or undersized existing electrodes must be corrected.

3. Bonding of EVSE Enclosure and Mounting Structure: Any metallic raceway (rigid metal conduit, intermediate metal conduit, or electrical metallic tubing) used to route EV charger wiring must be bonded. Where metal junction boxes, pull boxes, or mounting pedestals are used in commercial installations, each must be bonded back to the EGC. This is detailed in the Ohio EV Charger Installation Codes and Standards framework.

The EGC path must present low enough impedance that a ground fault will cause the circuit breaker to trip within the time limits specified by NEC 110.10. For a 40-ampere breaker serving a Level 2 EVSE, that generally requires the EGC loop impedance to be low enough to drive fault current above the breaker's instantaneous trip threshold — typically 10× the continuous rating for thermal-magnetic breakers.

Common scenarios

Residential Level 2 charger (240V, 32–48A): The most common Ohio residential installation routes a 40–60A circuit from the main panel to a garage or exterior wall-mounted EVSE. The EGC travels with the hot and neutral conductors. If the garage subpanel is fed by a feeder without an EGC (pre-1996 three-wire feeder), NEC 250.32 requires a separate grounding electrode at the garage, plus a new four-wire feeder or a documented exception — a frequent compliance gap found during Ohio inspections. See Electrical Panel Upgrades for EV Chargers Ohio for related panel considerations.

Commercial and fleet DC fast charger (480V, three-phase): DC fast chargers operating at 480V require grounding of both the EVSE cabinet and the cable management tray. NEC 250.97 requires bonding jumpers at concentric and eccentric knockouts where conduit enters the EVSE enclosure. Because DC fast chargers introduce high-frequency switching transients, some manufacturers specify supplemental bonding between the charger chassis and the concrete pad rebar, a requirement enforced through UL listing conditions rather than the NEC directly. The DC Fast Charger Electrical Infrastructure Ohio page addresses that infrastructure in depth.

Multifamily parking structures: Parking garage installations involve long conduit runs between a centralized electrical room and individual charging stations. Each metallic conduit section and junction box must be bonded. Where the conduit transitions from steel to PVC underground, an EGC must be pulled through the PVC section because PVC itself provides no bonding continuity. Ohio inspectors routinely flag missing EGCs at conduit-type transitions in Parking Garage EV Charging Electrical Systems projects.

Decision boundaries

Selecting the correct grounding method depends on two primary variables: installation type and wiring method.

For installations where an Ohio-Licensed Electrician identifies a pre-existing grounding electrode system deficiency, the deficiency must be corrected before the new EV circuit can be approved. Ohio does not allow an inspector to approve a new circuit while an existing code violation remains on the same service. This distinction between grounding (earth connection) and bonding (equipotential connection) is explained within the broader How Ohio Electrical Systems Work conceptual framework.

GFCI protection interacts directly with grounding: a properly grounded circuit allows the GFCI to detect imbalance between hot and neutral conductors at the 4–6 milliampere threshold, tripping before lethal current can flow. The GFCI Protection for EV Charging Equipment Ohio page covers that interaction in full. For an overview of all Ohio EV charger electrical topics, the site index provides a structured entry point to the full subject hierarchy.

References

• NEC Article 625 – Electric Vehicle Power Transfer System, NFPA 70 (2023 edition)
• NEC Article 250 – Grounding and Bonding, NFPA 70 (2023 edition)
• Ohio Board of Building Standards – Ohio Building Code
• UL 2594 – Standard for Electric Vehicle Supply Equipment, UL Standards
• NFPA 70E – Standard for Electrical Safety in the Workplace, 2024 edition (grounding hazard context)