Sourcing Locomotive Electrical and Electronic Parts

Mechanical parts wear out slowly and visibly. Electrical and electronic parts often fail suddenly, and a single failed relay or control card can stop a locomotive as completely as a broken engine part. They also go out of production much faster than mechanical parts, which makes sourcing harder as fleets age.

This guide covers the main types of locomotive electrical and electronic spares, how to identify them correctly, and the options when a part is obsolete.

What counts as electrical and electronic parts

On a diesel-electric locomotive, electrical and electronic spares cover a wide range:

• Switchgear: contactors, relays, reversers, switches and circuit breakers.
• Control electronics: control cards and modules, power supplies, interface units and displays.
• Sensors and instruments: pressure and temperature sensors, speed sensors, gauges and meters.
• Power components: transformers, rectifier parts, resistors and capacitors.
• Rotating machine parts: brushes, brush holders and related parts for traction motors, alternators and auxiliary machines, and starter motors.
• Wiring components: connectors, terminals, terminal boards, cable and harness parts.
• Lighting and cab equipment: headlights, marker lights, cab controls and switches.

Identify the part from its nameplate

Electrical parts that look alike can differ in ways that matter. Before ordering, record the nameplate or label data in full:

• Manufacturer and part number, including any suffix or revision.
• Rated voltage and current, and for relays and contactors the coil voltage separately from the contact rating.
• AC or DC, which is not always obvious from the size or shape.
• Contact arrangement: the number of normally open and normally closed contacts.
• Serial number and date code, which help identify the version.
• Mounting and connections: the base, fixing holes and terminal layout.

Many North American-design diesel-electric locomotives use a 74 V DC control system, but not all equipment on a locomotive runs at the same voltage. Never assume a coil voltage: read it from the part.

Photograph the nameplate, the terminals and the mounting before removing a part. If the label is damaged, the photos and the locomotive's parts catalogue together are usually enough to identify it.

When the part is obsolete

Electronics and some switchgear go out of production while the locomotives they fit still have years of service left. When a part is no longer made, there are several routes:

1. Remaining OEM or distributor stock

Some parts are still available from stock long after production ends. A supplier with good global contacts can often find them.

2. Equivalent parts

A part from another manufacturer may have the same function, ratings, size and mounting. The equivalent must match every important characteristic, not just the voltage and current. For safety-related circuits, an engineer should approve any substitution.

3. Repair of the original

Control cards, modules and some instruments can be repaired by replacing failed components. This keeps the original part in service but depends on the components themselves still being available.

4. Redesign

As a last resort, a part or sub-assembly can be redesigned using current components. This takes the most engineering effort but solves the problem for the long term.

Deomac supplies OEM and aftermarket diesel locomotive spares through reliable partners across the globe, and electrical and electronic parts are part of its locomotive range. The technical team can advise on specifications when you are looking for an alternative to an obsolete item.

Handling and storing electronic spares

Electronic spares can be damaged before they are ever fitted.

• Static protection. Keep control cards in their anti-static packaging until fitting, and handle them with proper grounding.
• Dry, clean storage. Moisture and dust damage contacts and circuit boards.
• Shelf life. Some components, such as electrolytic capacitors and certain seals, age in storage. Rotate stock and record receipt dates.
• Inspection on receipt. Check that labels, ratings and part numbers match the order before the part goes onto the shelf.
• Bench testing. Where you have the equipment, test spares before they are needed, not when a locomotive is waiting.

Find the cause, not just the part

A burnt contactor or a failed card is sometimes the result, not the cause. Loose connections, damaged insulation, moisture ingress, overloads or a fault elsewhere in the circuit can destroy a new part as quickly as the old one. Investigate the circuit before fitting the replacement.

What to send with an enquiry

For a quick, accurate quote, send Deomac:

• the manufacturer, part number and full nameplate data;
• photos of the part, its label, terminals and mounting;
• the locomotive type and where the part is fitted;
• quantities and the required date;
• whether you will consider equivalent or repaired parts.

Search the Deomac parts list first; our guide on how to search the Deomac rail parts list has tips on part numbers with separators. Then send the details through the contact page.

Related reading

• EMD and GE engine spares: a buyer's guide
• Coach parts: keeping passenger stock running, which covers coach lighting and auxiliary electrical parts

Summary

Electrical and electronic parts fail suddenly and go obsolete quickly. Record nameplate data in full, never assume voltages or contact arrangements, store and handle electronic spares carefully, and plan ahead for obsolete items through remaining stock, equivalents, repair or redesign.