Research · Paper 2 of 5
Charging level should not be used as a safety criterion
Should a residential charging permit distinguish between Level 1 (120 V) and Level 2 (240 V) charging? The engineering answer is no: electrical safety is determined by the design, certification, and installation of the charging equipment (EVSE), not by supply voltage alone.
Key finding
Regulate certified equipment, not charging level. Modern EVSE at both levels provides the same layered protections, and dedicated Level 2 installations often reduce improper use while substantially shortening the time a cable occupies the sidewalk.
How certified EVSE protects people
"EVSE" — Electric Vehicle Supply Equipment — is not an extension cord. Modern certified EVSE incorporates multiple independent layers of protection established through nationally recognized standards (NEC Article 625; UL 2594; UL 2231 Parts 1 & 2; SAE J1772):
- Ground-fault monitoring — current leakage trips the unit far below harmful thresholds.
- Equipment grounding verification — the unit confirms a proper ground path before operating.
- Communication handshake — the connector remains de-energized until the vehicle and charger complete a safety handshake; there are no exposed live parts at any point.
- Automatic disconnect — any fault condition shuts down charging immediately.
- Weather-rated enclosures and connectors — equipment designed for outdoor use in rain and snow.
These protections are identical in kind at Level 1 and Level 2. A pedestrian touching, stepping on, or tripping over an energized charging cable is protected by the same interlocks either way.
Practical safety comparison
| Safety consideration | Level 1 (120 V) | Level 2 (240 V) |
|---|---|---|
| Dedicated branch circuit | Not always | Typically required |
| Purpose-built installation | Varies | Typically yes |
| Continuous-load design | Variable | Designed for EV charging |
| Extension-cord temptation | Higher | Much lower |
| Sidewalk occupation time | Longer (often overnight or 20+ hrs) | Shorter (a few hours) |
| EVSE safety interlocks | Yes | Yes |
| Ground-fault protection | Yes | Yes |
The principal safety differences arise from installation practice and equipment configuration, not voltage. Level 1 charging typically uses an ordinary receptacle — which is precisely where improvised extension cords and worn household outlets enter the picture. A dedicated Level 2 installation is wired for continuous load, inspected under permit, and leaves little room for improvisation.
A counterintuitive result for sidewalk policy
A Level 1-only rule would maximize the hours a cable crosses the sidewalk each week — the very condition the permit seeks to minimize. Level 2 charging replenishes a typical week of driving in roughly three hours, shrinking both the exposure window for pedestrians and the temptation to leave equipment out.
A better regulatory standard
The permit program should require certified EVSE, installed in accordance with the National Electrical Code and manufacturer instructions, rather than regulating charging level. This relies on established national electrical safety standards instead of creating a local distinction that does not exist in those standards. There is no technical basis for treating Level 2 charging as inherently less safe than Level 1; the City's review should focus on certified equipment, proper installation, and safe operation.
Sources
- NFPA 70 (National Electrical Code), Article 625 — Electric Vehicle Power Transfer System.
- UL 2594 — Electric Vehicle Supply Equipment.
- UL 2231 Parts 1 & 2 — Personnel Protection Systems for EV Supply Circuits.
- SAE J1772 — Electric Vehicle Conductive Charge Coupler.
- U.S. Department of Energy, Alternative Fuels Data Center — Electric Vehicle Charging Infrastructure Basics.