Line-to-line voltage is the electrical potential difference measured between two live conductors (phases) in an AC power system. In three-phase networks, line-to-line voltage is the value most commonly used to specify supply levels (for example, 400 V in many European low-voltage grids). It directly impacts available charging power, equipment ratings, and how EV chargers are wired and protected.
What Is Line-to-line Voltage?
Line-to-line voltage (often written as V<sub>LL</sub>) is measured from one phase to another phase:
– In three-phase AC, it is the voltage between L1–L2, L2–L3, or L3–L1
– It is different from line-to-neutral voltage (phase voltage), which is measured between a phase and neutral (N)
In many standard low-voltage systems, the relationship is:
– V<sub>LL</sub> = √3 × V<sub>LN</sub>
That’s why 230 V line-to-neutral corresponds to about 400 V line-to-line in a typical three-phase supply.
Why Line-to-line Voltage Matters in EV Charging
Line-to-line voltage is a key parameter for sizing and deploying AC EV chargers, especially in commercial and public installations where three-phase charging is common. It affects:
– Maximum charging power available to the EV
– Cable sizing and voltage drop performance
– Protective device selection (MCBs, RCDs, surge protection)
– Charger configuration (single-phase vs three-phase)
– Compatibility with site electrical infrastructure and grid connection limits
For EV charging projects, line-to-line voltage is often part of the site’s electrical survey because it determines whether 11 kW or 22 kW AC charging can be supported reliably.
How Line-to-line Voltage Affects Charging Power
In AC charging, available power depends on voltage and current. For three-phase charging, line-to-line voltage is used in the power calculation:
– P ≈ √3 × V<sub>LL</sub> × I × PF
Where I is line current and PF is power factor (typically close to 1 for EV chargers).
Practical examples in a 400 V three-phase system:
– 11 kW charging typically uses about 16 A per phase
– 22 kW charging typically uses about 32 A per phase
If line-to-line voltage is lower than nominal (due to grid conditions or long cable runs), the charger may deliver less power or apply power throttling to stay within safe operating limits.
Common Line-to-line Voltage Levels
Typical low-voltage distribution values differ by region and site type:
– 400 V (three-phase) – common in European commercial sites
– 208 V (three-phase) – common in parts of North America
– 480 V (three-phase) – industrial and some commercial facilities (region dependent)
EV charger input specifications often list acceptable voltage ranges (for example, 380–415 V) to account for real-world grid variation.
Line-to-line Voltage vs Line-to-neutral Voltage
Understanding this distinction helps prevent wiring and specification errors:
– Line-to-line (V<sub>LL</sub>): phase-to-phase, used for three-phase ratings and power calculations
– Line-to-neutral (V<sub>LN</sub>): phase-to-neutral, used for single-phase loads and circuits requiring a neutral
Many AC chargers support both:
– Single-phase charging using L–N (typically 230 V)
– Three-phase charging using L1–L2–L3 (typically 400 V line-to-line)
Practical Considerations for Installers and Site Owners
Correctly confirming line-to-line voltage helps ensure safe, compliant installations:
– Verify site supply type: single-phase vs three-phase
– Confirm whether a neutral conductor is available and required
– Match charger rating to the supply (e.g., 22 kW requires three-phase with adequate current capacity)
– Account for voltage drop on long runs to avoid reduced charging performance
– Ensure protection devices match the system voltage and earthing arrangement (TN, TT, IT)
Related Glossary Terms
AC EV Charger
Three-phase charging
Line-to-neutral voltage
Voltage drop
Single-phase supply
Power factor
MCB (Miniature Circuit Breaker)
RCD (Residual Current Device)
Load balancing
Power throttling