From Decision Tree to a Real System

Our recent High-Voltage DC Fuse Selection Decision Tree laid out the voltage-tier logic for specifying Bussmann high-speed fuses across 500 V to 1500 Vdc. The most common follow-up question we received:

This guide is the answer. We walk through a standard 5 MWh / 2.5 MW containerized BESS — the most common configuration in the 2024–2026 utility-scale and C&I storage market — and give you the complete Bill of Materials (BOM) with the Bussmann part number specified at every protection point. By the end you will have a single reference for the entire protection architecture of a 1000 Vdc BESS container, with clear logic for why each Bussmann family was selected.

This article is the second in a two-part series. Read the fuse selection logic first: High-Voltage DC Fuse Selection Decision Tree: 500 V to 1500 V.

1. System Architecture Overview

A standard 5 MWh / 2.5 MW BESS container is built around a 1000 Vdc battery bus, with battery racks arranged in 2–4 strings feeding a central 2.5 MW Power Conversion System (PCS), then stepped up to 10–35 kVac for grid connection. The reference design we are specifying is based on a 20-foot high-cube ISO container (6.06 × 2.44 × 2.90 m) with 18 battery racks of 280 kWh each, liquid-cooled LFP cells.

Reference Design Specification

Main Single-Line Topology

Grid (10/35 kVac)

  └── MV transformer (2.5 MVA, Dyn11)

       └── MV switchgear with VCB + protection relay

            └── LV AC bus (400 Vac 3-ph)

                 ├── PCS #1 (1.25 MW) ──┐

                 └── PCS #2 (1.25 MW) ──┤

                                       DC bus (1000 Vdc)

                                       ├── Battery string 1 (6 racks × 280 kWh)

                                       ├── Battery string 2 (6 racks × 280 kWh)

                                       └── Battery string 3 (6 racks × 280 kWh)

            └── Auxiliary distribution (400/230 Vac)

                 ├── HVAC #1, #2  |  Fire suppression panel

                 ├── Lighting, outlets  |  EMS, BMS, comms rack

            └── Surge protection (AC + DC + signal)

The 5 MWh container is essentially three independent subsystems running in parallel: the high-voltage DC power path (battery ↔ PCS), the medium-voltage AC grid path (PCS ↔ grid), and the auxiliary system path (HVAC, fire, controls, comms). Each subsystem has its own protection philosophy and its own Bussmann family.

2. High-Voltage Battery System BOM

The battery system is the heart of the container — 18 racks of LFP modules, organized into three strings of 6 racks each. Each rack operates at 1000 Vdc nominal with a string current of approximately 1500 A at the DC bus.

2.1 Battery Rack (×18, identical)

Why 170M18XX and not 170M17XX: at 1000 Vdc nominal with operating transients reaching 1150 Vdc, the 17XX family's 800 Vdc rating is insufficient. The 18XX family provides the full 1000 Vdc rating with the same square-body form factor and DIN 43653 mounting. Selection rule from our decision tree: 1000 Vdc → 170M18XX.

Why 500 A and not higher: each rack contributes 6 × 280 Ah / 6 in parallel = 280 Ah at the string level, with a 1.5× derating margin for the rack fuse (1400 A string ÷ 18 racks = ~78 A per rack, but the rack fuse protects the rack-internal short circuit, not the string current — the proper sizing is per the I²t of the rack's contribution to a string short circuit, which falls in the 400–630 A range for a 52S LFP rack at 1000 Vdc). 500 A is the industry-consensus point.

2.2 Battery String Combiner (×3)

2.3 High-Voltage Box (HV-Box) — 1 per container

3. Power Conversion System (PCS) BOM

The PCS is the bidirectional inverter that connects the 1000 Vdc battery bus to the 400 Vac LV bus. For a 5 MWh container, the typical configuration is two parallel 1.25 MW units for redundancy and partial-load efficiency.

3.1 PCS Internal Protection (×2)

Why 170M17XX on the AC side even at 800 Vdc rating: the AC-side fuse is a back-up protection for the IGBT module. The IGBT's collector-emitter voltage rating is 1700 V, and the AC bus peak voltage is 400 × √2 = 565 V — well within the 170M17XX 800 Vdc rating. Using 170M18XX here is over-spec and cost-inefficient.

3.2 PCS Output to LV Bus

4. MV Transformer and Switchgear BOM

For grid connection, the 400 Vac LV bus is stepped up to 10 kVac (typical for small-to-medium BESS plants) or 35 kVac (for large utility plants).

4.1 MV Transformer

4.2 MV Switchgear

Why 170M58XX on the HV side: the MV transformer is protected by a dedicated bayonet fuse sized for the transformer inrush current (typically 8–12× rated for 0.1 s). The 170M58XX family provides the high I²t withstanding needed for transformer energization while still offering fast enough operation for internal HV faults. For BESS applications with frequent charge/discharge cycles, the high cycle count of the 58XX series (vs. NH-style fuses) is a secondary benefit.

5. LV AC Distribution BOM

Why RT16 / NH1 gG on the AC side: as discussed in our Depot Infrastructure Protection Guide, the RT16 / NT00 / NH1 gG series is the European/IEC standard for AC distribution protection. gG (general-purpose, full-range breaking) covers both overload and short-circuit, making it the right choice for fixed loads like HVAC and lighting.

6. HVAC and Fire Suppression BOM

The auxiliary systems keep the battery at optimal temperature and contain any thermal event. They are protection-critical, not just comfort.

6.1 HVAC (Liquid Cooling)

Why aM on the compressor and gG on the pump: compressor loads have very high locked-rotor current (5–7× full load) that would nuisance-trip a gG fuse during startup. aM (motor protection) class fuses have a higher inrush tolerance while still protecting against short circuits.

6.2 Fire Suppression

7. EMS, BMS, and Communications BOM

The energy management system (EMS), battery management system (BMS), and communication network are the brain of the container. They are also the subsystem most often built with consumer-grade components that fail in the field — particularly the physical connectors.

The connector point is critical. In a 5 MWh container operating at 10–55 °C ambient with daily thermal cycling, vibration from HVAC, and 24/7 uptime, consumer-grade USB or RJ45 jacks will fail within 12–18 months. Industrial-grade locking connectors with IP67 sealing and -40 to +85 °C temperature range are the only reliable choice.

GSCONN supplies industrial-grade locking USB Type-A, Type-C, and stacked-port configurations designed for EV charging and BESS cabinet environments — the same physical interfaces built to the same field demands as the Bussmann protection package.

8. Container Enclosure BOM

9. Complete Bussmann Protection Map (Single-Reference Table)

Total Bussmann part count: approximately 50–55 protection devices per 5 MWh container, excluding the medium-voltage switchgear (which is a separate Eaton product line).

10. Selection Checklist (5 MWh Container)

Use this checklist when reviewing or specifying a 5 MWh containerized BESS:

[ ] DC bus voltage confirmed at 1000 Vdc nominal, with full operating range (typically 800–1150 Vdc)

[ ] Rack-level fuse sized at 500 A with 170M18XX (1000 Vdc / 50 kA / tc=1 ms)

[ ] String main fuse sized at 800 A with 170M18XX

[ ] HV-Box main fuse sized at 1250 A with 170M5813D (Size 3) — verify thermal coordination with disconnect switch

[ ] PCS DC fuses matched to IGBT module I²t (verify with PCS vendor's coordination curve)

[ ] PCS AC fuses sized for 800 Vdc / 800 A (170M17XX) — back-up only

[ ] MV transformer bayonet fuse coordinated with inrush and secondary LV breaker let-through

[ ] AC SPD upstream of PCS (Type 1+2, 25 kA, 400 Vac)

[ ] DC SPD at HV-Box input (Type 2, 40 kA, 1000 Vdc)

[ ] HVAC compressor fuses are aM class (not gG)

[ ] Fire suppression has dedicated branch circuit, not shared with HVAC

[ ] Industrial connectors specified for all external ports (USB, RJ45, fiber, coax) — no consumer-grade

[ ] IP rating of enclosure confirmed at IP55 minimum; cable entries IP67

[ ] Standards compliance verified: UL 9540A, IEC 62619, GB/T 36276, NFPA 855

[ ] Thermal management verified: HVAC capacity (40 kW liquid cooling per string), BMS thermal sensors per cell

[ ] Ground fault detection at the string level (Bender IR155 or equivalent)

[ ] Insulation monitoring at the DC bus (Bender ISOMETER or equivalent)

[ ] Door interlocks mechanically interlocked with main disconnect, electrically interlocked with PCS