Space is the ultimate constraint in EV power electronics and energy storage systems (ESS). Onboard chargers (OBC), DC-DC converters, and battery junction boxes have strictly limited enclosure volumes -- and the DC fuse protection devices must fit within those constraints while still providing full-rated voltage and interrupting performance. The Eaton Bussmann CBX series achieves this with a compact square-body design delivering 800 Vdc and 1000 Vdc protection at significantly reduced body lengths compared to the standard 170M series: approximately 106 mm body length for a 400A CBX01S vs. approximately 150 mm for the equivalent 170M18XX.

For engineers designing high-density EV charging infrastructure and battery energy storage systems, selecting the right compact DC fuse involves balancing dimensional constraints, interrupting ratings, and DC time constant compatibility. This guide compares the CBX series against the established 170M platform and provides application-specific selection guidance.

CBX vs 170M: Dimensional and Performance Comparison for DC Applications

CBX01S 1000Vdc Fuse: Electrical Data and Specifications

The CBX01S series provides 1000 Vdc protection with 50 kA interrupting rating at tc=10 ms. Below is the complete electrical data for the CBX01S-1000 product line:

All CBX01S ratings are proven at 1000 Vdc with time constant at most 10 ms and interrupting rating (IR) of 50 kA. Both without-indicator (N suffix) and Type K microswitch indicator versions are available -- the indicator enables remote monitoring of fuse status via a microswitch signal to the system BMS or SCADA.

CBX000S 800Vdc Fuse: Applications in EV and BESS

The CBX000S covers the 800 Vdc tier with ratings from 32A to 630A. Key applications include on-board charger DC bus protection (OBC enclosures have strict height constraints), DC-DC converter output protection in 800V EV platforms, and ESS module-level protection in 800V battery energy storage systems where compact fuse dimensions enable higher packing density. The tc=10 ms characteristic is more tolerant of DC bus inductance from long cable runs or LC filters.

DC Time Constant Selection: tc=10 ms vs tc=1 ms for EV Charger Design

The tc=10 ms rating (CBX) reflects a different DC time constant than the tc=1 ms rating (170M). Selecting the correct time constant is critical for reliable DC fuse operation in EV charging and energy storage applications:

CBX tc=10 ms -- High-inductance DC bus applications

Multi-module charger architectures with DC busbars spanning several modules

Systems with large output filter inductors

Long cable runs between charger and vehicle

170M tc=1 ms -- Low-inductance DC bus applications

Direct battery connection

Short busbar runs

Low-inductance capacitor banks typical of high-performance EV inverter DC buses

For most EV charger DC bus applications, both are suitable, with CBX tc=10 ms providing conservative margin against the cable inductance that typically characterizes long charging cable runs.

Frequently Asked Questions About Compact DC Fuses for EV Applications

What is the shortest 1000Vdc fuse available for EV charger applications?

The Eaton Bussmann CBX01S series provides 1000 Vdc protection in approximately 106 mm body length for ratings up to 400A. This compares to approximately 150 mm for the equivalent 170M18XX series. The 44 mm length reduction enables higher packing density in space-constrained EV charger and OBC enclosures.

What does tc=10 ms mean for DC fuse selection?

The DC time constant (tc) represents the L/R ratio of the circuit the fuse must interrupt. A tc=10 ms rating means the fuse is tested and proven to interrupt 50 kA in a circuit with 10 milliseconds time constant. This is more tolerant of systems with cable inductance and filter components. The 170M series tc=1 ms rating is tested in lower-inductance circuits and is suited for direct battery connections.

Can CBX fuses replace 170M fuses in existing EV charger designs?

Yes, with verification. The CBX series has similar body width to 170M, so mounting hardware is often compatible. However, the tc=10 ms vs tc=1 ms difference must be evaluated against the actual DC bus inductance of the specific charger design. For systems with long cable runs or filter inductors, CBX tc=10 ms may actually provide better protection margins.

What is the difference between CBX01S and CBX000S?

CBX01S is rated for 1000 Vdc with current ratings from 32A to 400A. CBX000S is rated for 800 Vdc with current ratings from 32A to 630A. The voltage rating determines which series is appropriate: 1000 Vdc systems (high-voltage EV platforms, 1500Vdc ESS with series strings) use CBX01S; 800 Vdc systems (standard EV platforms, 800V BESS modules) use CBX000S.

How do I select the correct CBX fuse rating for my DC bus?

Start with the continuous operating current of the DC bus, then apply a derating factor for ambient temperature and enclosure conditions. Verify the fuse's total I2t is less than the semiconductor's withstand I2t. Confirm the interrupting rating (50 kA for CBX) exceeds the maximum prospective short-circuit current. Finally, match the DC time constant (tc=10 ms) to your circuit's L/R characteristics.