The size of the transformer and cables needed for charging stations depends on several factors, including the number of charging points, the power requirements of each charger, and the expected simultaneous usage (load). Below are general guidelines for determining the transformer and cable sizes:

1. Transformer Sizing

The transformer size is typically calculated based on the total power demand of the charging stations, considering diversity factors (not all chargers may be used simultaneously).

Level 2 Chargers

  • Power requirement per charger: 6.6 kW to 22 kW.
  • Typical transformer size for multiple Level 2 chargers: 150 kVA to 500 kVA, depending on the number of chargers.

DC Fast Chargers

  • Power requirement per charger: 50 kW to 350 kW.
  • Typical transformer size:
    • For 2-4 chargers: 250 kVA to 500 kVA.
    • For larger installations with multiple chargers (e.g., 10 or more): 1,000 kVA or larger.

2. Cable Sizing

Cable size is determined based on the following:

  • Current Carrying Capacity: The maximum current the cable can safely carry without overheating.
  • Voltage Drop: To minimize losses, voltage drop should typically be less than 3% over the cable length.
  • Environmental Factors: Cable insulation type and installation conditions (e.g., buried underground, exposed to air).

Level 2 Chargers

  • For single chargers (6.6 kW at 240V): ~30A circuit, requiring 6 AWG copper or 4 AWG aluminum.
  • For multiple chargers on a single circuit: Use feeder cables sized for total demand.

DC Fast Chargers

  • For 50 kW (e.g., 480V, ~105A): 1 AWG copper or 1/0 aluminum.
  • For 150 kW chargers (e.g., 480V, ~315A): 350 MCM or larger, depending on distance.

3. Other Considerations

  • Demand Load Management: Systems that control and balance load can reduce the peak demand and allow for smaller transformers and cables.
  • Future Expansion: Installations should account for future scaling, which may require oversizing transformers and cables initially.
  • Code Compliance: Always adhere to local electrical codes (e.g., NEC in the U.S.) for safe and legal installations.
  • Distance: Longer distances require larger cables to compensate for voltage drop.

Example Calculation

For a station with four 150 kW DC fast chargers (total 600 kW) at 480V:

  • Transformer: Typically 750 kVA or 1,000 kVA.
  • Feeder Cable: Depends on distance; for short runs, ~500 MCM copper or equivalent aluminum may suffice.

Engaging a licensed electrical engineer is essential for precise calculations and ensuring compliance with applicable standards.