Complete Guide to EV Charging Infrastructure Voltage Drop
Everything electrical contractors need to know about sizing circuits for Level 2 and DC fast EV chargers, from residential installations to commercial charging stations.
Electric vehicle adoption is accelerating rapidly, creating enormous demand for charging infrastructure. For electrical contractors, EV charger installations represent a growing market—but also present unique voltage drop challenges that require careful attention to ensure customer satisfaction.
Why Voltage Drop Matters for EV Charging
EV chargers are continuous loads, often drawing high current for extended periods. Unlike typical appliances that cycle on and off, a Level 2 charger may draw 40-80 amps continuously for 8-12 hours overnight. This continuous operation amplifies the effects of voltage drop—the charger will operate at reduced power, extending charge times and potentially frustrating customers who expected faster charging.
Additionally, many EV chargers are installed in garages or parking structures far from the electrical panel, creating long circuit runs where voltage drop becomes the controlling design factor rather than ampacity.
EV Charger Types and Power Requirements
| Type | Voltage | Current | Power | Miles/Hour |
|---|---|---|---|---|
| Level 1 | 120V | 12-16A | 1.4-1.9 kW | 3-5 |
| Level 2 (Basic) | 240V | 16-32A | 3.8-7.7 kW | 12-25 |
| Level 2 (High) | 240V | 40-80A | 9.6-19.2 kW | 25-50 |
| DC Fast Charge | 480V 3Φ | 60-420A | 50-350 kW | 180-1000 |
Residential Level 2 Installations
Most residential EV charger installations use 240V Level 2 equipment rated for 40-48 amps. The most common scenario is a Tesla Wall Connector or similar charger in an attached or detached garage.
Example: 48A Charger at Various Distances
Using 240V single-phase, copper conductors
| Distance | 6 AWG | 4 AWG | 3 AWG |
|---|---|---|---|
| 50 ft | 1.96% | 1.23% | 0.98% |
| 100 ft | 3.93% | 2.46% | 1.96% |
| 150 ft | 5.89% | 3.70% | 2.94% |
| 200 ft | 7.85% | 4.93% | 3.92% |
As the table shows, even a modest 100-foot run to a detached garage can push voltage drop over 3% with minimum-sized conductors. Always verify voltage drop before finalizing your design.
Commercial Charging Stations
Commercial EV charging installations present additional challenges: multiple chargers, longer runs to parking areas, and the need for load management systems. Key considerations include:
- Sub-panel Placement: Install a sub-panel in or near the parking structure to keep branch circuit runs short.
- Load Management: Smart chargers can share capacity, reducing feeder sizing requirements.
- Future Expansion: Size feeders for anticipated growth, not just initial installation.
Size Your EV Charger Circuit
Use our voltage drop calculator to properly size conductors for EV charger installations. Ensure full charging performance and avoid costly callbacks.
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