Grounding, Bonding & Fault Paths
Equipment grounding conductors, bonding jumpers, neutral-ground separation, metallic raceway bonding, and subpanel requirements.
- Explain the purpose and sizing of equipment grounding conductors for EVSE
- Describe bonding jumper requirements and why continuity is essential
- Explain neutral-ground separation in subpanels feeding EVSE
- Identify short-circuit current rating (SCCR) requirements for EVSE
- Describe multi-wire branch circuit risks when adding EVSE
Lesson 1
Equipment Grounding Conductors & Fault Paths
Why EGC Is Critical for EVSE
The equipment grounding conductor (EGC) is the safety conductor that connects the metal enclosure of the EVSE and all non-current-carrying metal parts back to the electrical panel's grounding bus. Its purpose is to provide a low-impedance fault current path so that if a hot conductor contacts the metal enclosure, the resulting high fault current will trip the overcurrent device quickly.
Without a proper EGC, a ground fault could energize the EVSE enclosure and the connected vehicle chassis. Anyone touching the vehicle or charger would be in the fault path - a potentially lethal situation. This is why the EGC is critical for every EVSE installation.
Safety Critical
The EGC provides the fault current return path that allows the breaker to trip. If the EGC is missing, undersized, or has a poor connection, a ground fault may not clear - leaving dangerous voltage on the EVSE and vehicle indefinitely.
EGC Sizing
The EGC must be sized per NEC Table 250.122 based on the rating of the overcurrent device protecting the circuit. For a 50A EVSE circuit, the minimum EGC size is 10 AWG copper. For a 60A circuit, the minimum is 10 AWG copper as well. For circuits 100A and above, the EGC size increases to 8 AWG copper.
| Breaker Rating | Minimum Copper EGC |
|---|---|
| 15A - 20A | 12 AWG |
| 30A | 10 AWG |
| 40A - 60A | 10 AWG |
| 100A | 8 AWG |
| 200A | 6 AWG |
Fault Path Integrity
The EGC must provide a continuous, low-impedance path from the EVSE enclosure to the service panel grounding bus. Every connection point - at the panel, at any junction box, at the EVSE - must be properly terminated and torqued. A single loose connection or corroded terminal can increase impedance enough to prevent the breaker from tripping during a fault.
The EGC is critical for EVSE because it provides the low-impedance fault current path that allows the breaker to clear a ground fault. Size the EGC per NEC Table 250.122 based on the overcurrent device rating. A broken or loose EGC creates a life-threatening hazard.