Rolling stock presents one of the harshest environments for any protective device: constant vibration, wide temperature swings, dust, humidity, and — most significantly — high DC voltages that must be interrupted reliably, every time, for decades.

Bussmann has supplied railway traction fuses for generations. The 170M, 170E, KC36, RCSF, NBC, FWK, LRC750, and FWL series cover the full spectrum of rail applications from 750VDC third-rail systems to 4000VDC high-speed traction.

This guide explains the railway fuse landscape and how to select.

Why Railway Fuses Are Different

1. Extreme DC Voltages

Rail systems use DC traction power: 750VDC (light rail, metros), 1500VDC (mainline), 3000VDC (some high-speed, older systems), and up to 4000VDC in advanced applications. Fuses must interrupt these DC arcs reliably — no AC zero-crossing to help.

2. Vibration and Shock

Per EN 61373, rolling stock equipment must survive constant vibration across a wide frequency spectrum. Fuse elements, fill material, and terminal connections must all withstand years of this.

3. Wide Temperature Range

From -40°C (cold climates) to +70°C (under-hood, hot climates), railway fuses must perform consistently across the full range.

4. Long Service Life

Rail vehicles have service lives of 30–40 years, often with mid-life refurbishment. A fuse specified today may still be in service in 2065 — and must be available for replacement.

5. Standards Compliance

Railway equipment must meet EN 50155 (electronic equipment on rolling stock), EN 50124 (insulation coordination), and often EN 45545 (fire safety).

The Bussmann Railway Fuse Portfolio

170M Series — Third-Rail and Traction

The 170M series is the backbone of Bussmann's railway offering. Standard 170M models cover 750VDC, with dedicated traction variants for higher voltages.

170E Series — Extended Voltage Range

The 170E series extends the 170M design to higher voltages:

Dedicated Railway Series

Railway Application Map

Application 1: Traction Converter Input

The main traction converter takes DC from the catenary/third rail and produces AC for the traction motors.

Application 2: Auxiliary Converter (Static Inverter)

Powers lighting, HVAC, door systems, and passenger information.

Application 3: Battery Charger / Onboard Battery

Application 4: Third Rail Pick-Up Protection

Application 5: Signaling and Track Circuits

Selection Considerations for Rail

1. Voltage Rating with Margin

Rail systems experience voltage transients during regeneration, switching, and fault clearing. Select a fuse with rated voltage at least 20% above nominal.

Example: 1500VDC nominal → select a fuse rated ≥ 1800VDC, or verify the fuse's transient withstand rating.

2. Time Constant Matching

Traction circuits often have a specific L/R time constant that affects the fault current rise. The fuse's DC breaking capacity is specified at a particular time constant — verify it matches the circuit.

3. Vibration Resistance

Verify the fuse is tested to EN 61373 Cat 1 Class B (body-mounted) or the applicable category. Bussmann railway fuses carry this qualification.

4. Fire Safety

For rolling stock, EN 45545 requires materials to meet fire behavior categories. Bussmann railway fuses use materials compliant with HL1–HL3 as required.

5. Availability for the Vehicle Life

Specify a fuse series in continuous production. Bussmann's railway fuses are supported long-term due to the industry's extended service life requirements.

Worked Example: Metro Traction Converter (750VDC)

System parameters: - Catenary voltage: 750VDC nominal, 900VDC maximum - Traction converter input current: 480A - Maximum fault current: 35kA - Time constant: 10ms

Selection: 1. Voltage: 900VDC max → select 1000VDC-rated fuse (margin) 2. Current: 480A × 1.25 = 600A 3. Selected: 170M26xx (1000VDC, 600A) family, or KC36 railway-specific 4. Verify: breaking capacity ≥ 35kA at 1000VDC ✓

Indication: Pair with 170H0069 microswitch for cab-mounted fuse-failure indication.

Worked Example: Light Rail Third-Rail (750VDC)

System parameters: - Third rail voltage: 750VDC - Pick-up current: 800A - Fault current: 25kA

Selection: 1. Voltage: 750VDC → 750VDC-rated fuse acceptable (verify transient margin) 2. Current: 800A × 1.2 = 960A 3. Selected: 170M15xx or LRC750 (railway third-rail series) 4. Mounting: railway-rated base with vibration qualification

Standards Reference

Separate the traction domains

A traction substation contains AC transformer protection, rectifier semiconductor protection and DC feeder protection. On the train, converters, auxiliary supplies, battery chargers and HVAC create additional layers. Each layer has a distinct fault-current source and time-current objective.

Eaton's Bussmann high-speed portfolio includes products for harsh DC traction applications at high voltage and current, but the family name alone does not establish a catalog number's DC rating. Always use the model's published AC/DC data and the system time constant.

Protect power semiconductors with energy data

For rectifiers and traction converters, compare fuse pre-arcing and total clearing I²t with the semiconductor withstand. Include cyclic loading, overload events, cooling and the peak arc voltage the circuit can tolerate.

A branch or feeder fuse protects conductors and switchgear; a high-speed fuse protects diodes, thyristors, IGBTs or SiC modules. These functions may be coordinated, but one device does not automatically replace the other.

Design for service continuity

Coordinate feeder protection so a local third-rail, overhead-line or rolling-stock fault does not unnecessarily remove an entire traction substation. Check both high-current faults and lower-current, high-resistance faults.

Onboard, group essential auxiliaries so a converter fault does not disable unrelated braking, door, communications or control functions. Record the approved replacement fuse in the vehicle maintenance documentation.

Account for motion and environment

Verify vibration and shock capability for the exact mounting orientation and duty.

Control bolted-joint torque and busbar alignment; high-speed fuses are not structural supports.

Include ambient temperature, tunnel heat and repeated acceleration/regeneration cycles in current derating.

After a fuse operates, inspect the converter and insulation before restoring service.

Bussmann model references to evaluate (editorial)

Selection note: These are editorial model references, not a bill of materials. Confirm current, voltage, interrupting rating, time-current curve, I²t, mounting, approvals and latest datasheet before specification.

Common Questions

Q: Can I use a standard 170M for railway? A: Only if it's rated for the voltage and qualified for the environment. Many standard 170M models do not carry EN 61373 vibration qualification. Specify railway-qualified variants.

Q: What's the difference between KC36 and 170M? A: KC36 is a railway-specific series optimized for traction converter DC links, with a time-current curve tuned to railway fault profiles. The 170M is a more general high-speed industrial fuse that also serves railway (and many other) applications.

Q: How do I know a fuse meets EN 45545? A: The datasheet or the manufacturer's railway documentation will state the fire behavior classification (HL1, HL2, HL3). Bussmann railway fuses are documented per the relevant hazard level.

Q: Is there a "railway-only" fuse holder? A: Yes — railway applications use holders with EN 61373 vibration qualification and appropriate insulation for the DC voltage. Confirm the base's qualification when specifying.

Written by the asbeam.com technical team. Reference: Eaton Bussmann Traction Fuses Catalogue (CA132022EN). asbeam supplies Bussmann railway and traction fuses with qualification documentation. Contact us for rolling-stock projects.

Further reading: - 170M High-Speed Fuse Guide - FWH, FWP, FWE & FWJ Semiconductor Fuse Guide - Medium Voltage Fuse Selection