Fleet Depot Charging: Different from Public DCFC

Commercial electric fleet vehicles operate on depot charging schedules rather than public fast-charging networks. A typical fleet depot might have 10-50 chargers serving 50-200 vehicles, with most vehicles charging simultaneously overnight or during midday layovers. This creates electrical challenges distinct from public DCFC: high utilization at 16-20 hours per day at 50-100% load factor; multi-vehicle coordination with complex fault current contributions from multiple chargers on a shared transformer; building electrical integration with existing 400 Vac infrastructure; and long cable runs of 30-50m from charger to vehicle.

Depot Charger Architecture and Bussmann Protection

AC Side Protection: RT16/NT gG Fuses

 For a 150 kW three-phase charger at 400Vac: I = 150,000 / (400 x 1.732) = approximately 216A per phase. Recommended RT16-2 (NT2) fuse rated at 250A provides 116% margin, AC 500V rating sufficient for 400Vac, and 120kA AC interrupting capacity. This single protective device provides backup protection for the downstream DC bus, cable protection for the AC input wiring, and selective coordination with the upstream transformer protection.

DC Side Protection: 170M or CBX Fuses

The DC output bus of depot chargers is the most critical protection zone. Vehicle-side faults from damaged charging cable or contaminated inlet can inject high fault currents; the DC bus has no natural zero-crossing to extinguish arcs; and fault clearing must be coordinated with the vehicle's onboard protection. Bussmann 170M17XX (800 Vdc, 50 kA, tc=1 ms) is specified when DC bus inductance is low and direct battery connection is used. CBX000S (800 Vdc, 50 kA, tc=10 ms) is specified when the DC bus includes significant inductance from long cable runs or multi-module architecture -- the tc=10 ms characteristic is more tolerant of high-inductance fault current waveforms.

Multi-Charger Fault Coordination

In a depot with 20 x 150 kW chargers on a common transformer, available fault current can reach 30-50 kA. Protection coordination studies must verify three conditions: the transformer secondary ACB trips before individual charger fuses for upstream bus faults; individual charger DC fuses clear before transformer secondary protection for vehicle-side faults; and no two chargers' fuses blow simultaneously for a single vehicle-side fault (selectivity requirement). This typically requires a hierarchy of AC protection (ACB upstream, RT16 at charger AC input, charger internal fuse) with DC protection at the charger output dedicated to vehicle-side faults.