Question 1

What size transformer does an EV charging station need?

Accepted Answer

It depends on the number of chargers, the power rating per charger, and the diversity (coincidence) factor for the site — not a fixed number. A single dedicated high-power DC fast charger (150–350 kW) is often served by a unit in the sub-1 MVA range, while a multi-stall hub with several >240 kW chargers typically falls in the 500–5000 kVA range. We size each project to the actual connected and coincident load.

Question 2

Do DC fast chargers need a dedicated transformer?

Accepted Answer

Large hubs and dedicated charging sites generally use a dedicated transformer so the sustained, near-continuous charging load doesn't compete with or affect other building or site loads. Smaller installations — one or two chargers added to an existing facility — may be served by existing service capacity if there's sufficient headroom; a load study determines which approach fits.

Question 3

Pad-mounted vs. indoor transformer for EV charging — which do I need?

Accepted Answer

Outdoor sites — highway corridors, retail lots, standalone charging hubs — typically use tamper-resistant, weatherproof pad-mounted transformers built to ANSI C57.12.26. Indoor and structured-parking installations use dry-type transformers, which eliminate oil handling and simplify fire code compliance for an indoor location.

Question 4

What kVA transformer do I need for a hub with multiple fast chargers?

Accepted Answer

Total connected load (sum of each charger's rated power) is the starting point, but actual sizing applies a diversity/coincidence factor since not every charger draws peak power simultaneously. Multi-charger hubs with several >240 kW units commonly land in the 500–5000 kVA range; we work from your specific charger count and power ratings to size the unit correctly rather than defaulting to a standard size.

Question 5

How do you handle continuous high-load operation at charging sites?

Accepted Answer

Charging hubs can sit at or near full load for extended periods, unlike typical intermittent commercial loads. We design for continuous-load service with temperature-rise margin engineered for sustained high utilization, avoiding the accelerated insulation aging that comes from undersizing a transformer for what is effectively a near-continuous-duty application.

EV Charging Transformers | DC Fast Charging | Seatrust