Industrial Ethernet migration is no longer a future roadmap item. In June 2026, HMS Networks reported that Industrial Ethernet accounts for 79% of newly installed industrial network nodes, while fieldbus has fallen to 14%, forcing manufacturers to decide what to keep, price, and consign from legacy DeviceNet, ControlNet, PROFIBUS, Modbus RTU, Remote I/O, gateways, switches, and PLC communication modules (HMS Networks via MarketScreener).
For plant managers and procurement teams, this is not just a controls-engineering issue. It is an excess inventory issue, a downtime-risk issue, and a timing issue. The same migration that modernizes production can leave cabinets full of mixed-value surplus parts: some are critical insurance for lines still running legacy fieldbus, while others should be documented, priced, and moved before the buyer pool narrows.
Why 2026 Is a Decision Point for Legacy Fieldbus Spares
The demand curve is splitting. Legacy fieldbus parts are not becoming worthless overnight. Many plants still operate DeviceNet, ControlNet, PROFIBUS, Modbus RTU, and Remote I/O segments because the connected I/O, drives, valve banks, weigh modules, and controllers still perform their jobs. But new installations are concentrating around EtherNet/IP, PROFINET, EtherCAT, and Modbus TCP. That means future demand for legacy fieldbus spare parts will increasingly come from two groups: plants still maintaining installed architectures, and integrators supporting phased migrations.
That split matters for resale value. A tested PLC communication module tied to a still-common installed platform may remain attractive to a buyer trying to prevent downtime. A box of unverified, unlabeled fieldbus adapters from a decommissioned line may not. The difference is not simply protocol age; it is documentation, condition, compatibility, and urgency.
HMS reported that PROFINET, EtherNet/IP, and EtherCAT together now represent roughly three-quarters of the wired protocol market, while PROFIBUS dropped to 4% of new nodes and DeviceNet and CAN/CANopen remain in the 1–2% range (HMS Networks via MarketScreener). That does not mean every PROFIBUS card or DeviceNet scanner should be liquidated immediately. It means procurement should stop treating fieldbus inventory as a single bucket.
Manufacturing conditions also support action. ISM reported that U.S. manufacturing expanded in May 2026 for the fifth consecutive month, with the Manufacturing PMI at 54% and new orders also expanding (Institute for Supply Management via PRNewswire). When production activity improves, maintenance and project teams are more likely to buy urgent spares, complete deferred upgrades, and source discontinued parts outside standard distribution.
For manufacturers holding excess automation parts, that creates a practical window: audit while the installed base still needs the parts, not after every plant in your sector completes the same migration.
📊 By the Numbers: Industrial Ethernet reached 79% of new industrial network nodes in HMS Networks’ 2026 analysis, while fieldbus fell to 14%. Treat that as a signal to segment your fieldbus inventory by operational need and resale potential, not as a reason to scrap everything.
Build a Fieldbus Surplus Audit Around Network Function
Start with function, not shelf location. A storeroom export that says communication card or network module is not enough. The same part family can include a line-critical scanner, a duplicate gateway, a low-value terminal block, or an obsolete adapter with no documented condition. Controls, maintenance, and procurement should classify each item by how it participates in the automation architecture.
A useful industrial Ethernet migration spare parts audit should separate inventory into these groups:
- PLC communication modules — DeviceNet scanners, ControlNet bridges, PROFIBUS masters, Remote I/O adapters, Ethernet bridges, serial cards, and backplane communication modules.
- Remote I/O and fieldbus adapters — distributed I/O heads, bus couplers, terminal bases, specialty analog modules, and network-specific adapters.
- Gateways and protocol converters — DeviceNet-to-EtherNet/IP, PROFIBUS-to-PROFINET, Modbus RTU-to-Modbus TCP, serial-to-Ethernet, and multi-protocol bridges.
- Industrial switches and media hardware — managed switches, fiber converters, taps, repeaters, terminators, connectors, and network power supplies.
- Migration leftovers — parts removed from lines already converted to EtherNet/IP, PROFINET, Modbus TCP, or EtherCAT.
Then attach line context. For every item, document the machine, line, controller family, protocol, firmware if visible, and whether the part supports a line that is still running. A DeviceNet module that matches three active packaging lines is not the same as a DeviceNet module pulled from a retired cell. A PROFIBUS I/O card with known compatibility to an active Siemens platform should not be grouped with untested surplus from a cleanout.
This is also where safety-stock logic matters. If your plant has already reset PLC and VFD spares around current lead-time risk, reuse that discipline here. The same keep-or-sell framework in a 2026 MRO safety-stock reset applies to network modules: retain the minimum credible downtime coverage, then evaluate duplicates for resale.
| Inventory category | Keep on site when... | Price or consign when... | Documentation that improves value |
|---|---|---|---|
| DeviceNet scanners and adapters | Active lines still depend on the segment and no validated spare exists | Multiple tested duplicates exist after migration | Catalog number, firmware, photos, test status, line removed from |
| ControlNet bridges and modules | The module supports a critical controller architecture still in service | The matching line has converted to EtherNet/IP or has excess redundancy | Series/revision, firmware, conformal coating status if visible |
| PROFIBUS masters and I/O cards | Siemens or mixed-vendor cells still use PROFIBUS devices | The site has standardized on PROFINET and has more than required safety stock | GSD file reference if known, part number, installed base notes |
| Remote I/O adapters | Legacy racks remain installed and are expensive to re-engineer | Racks were removed intact and modules are clean, labeled, and boxed | Rack position, terminal base, removable connector status |
| Gateways and protocol converters | Needed for phased migration or bridge architecture | The migration is complete and the gateway is no longer part of the standard | Protocol pair, configuration backup, power-up test result |
| Managed industrial switches | Required for current Ethernet segmentation or diagnostics | Upgraded network design left clean, functional spares | Port count, speed, managed/unmanaged status, configuration cleared |
Do not ignore gateways. As plants move from legacy networks to Ethernet-era architectures, gateways often remain useful longer than the networks they bridge. Automation Distribution notes that EtherNet/IP, PROFINET, and Modbus TCP can share physical Ethernet infrastructure but do not automatically exchange I/O data at the application layer without a gateway or multi-protocol controller (Automation Distribution). That makes certain protocol converters valuable to buyers still staging migrations.
📋 Pro Tip: Audit by protocol, controller ecosystem, and line status. A part labeled simply as network module is hard to value; a tested PROFIBUS master removed from a Siemens cell during a documented PROFINET upgrade is a much clearer resale asset.
Decide What to Keep, What to Price, and What to Consign
Not every legacy network spare should leave the plant. DeviceNet and ControlNet remain embedded in many mature automation environments. Industrial Ethernet Blog describes typical hybrid OT architectures where EtherNet/IP backbones coexist with DeviceNet and ControlNet segments that still run production, and recommends disciplined baselining, tested spares, and phased migration rather than unmanaged risk (Industrial Ethernet Blog).
That should shape the disposition decision. The goal is not to maximize short-term cash at the expense of uptime. The goal is to stop storing five, ten, or twenty duplicate modules when one or two tested spares would cover realistic downtime risk.
Keep: critical, tested, architecture-matched spares
Keep parts that match active risk. A critical spare is not critical because it is old. It is critical because failure would stop production, the part is difficult to replace quickly, and the plant has not yet migrated the connected architecture. Retain at least one tested spare for active DeviceNet scanners, ControlNet bridges, PROFIBUS communication processors, and Remote I/O adapters that support high-value lines.
Also keep specialty parts where the replacement path requires program changes, revalidation, panel rewiring, or safety review. A low-dollar module can carry high operational risk if replacement triggers engineering work during a breakdown.
Price: clean duplicates with identifiable demand
Price duplicates before they become mystery inventory. If a plant is sitting on 12 identical DeviceNet adapters after a line conversion and only two active segments remain, the extras deserve a resale review. If a plant has 40 PROFIBUS I/O cards from a retired cell, the first question is whether they are clean, labeled, and tied to a known platform. If they are, they may be candidates for consignment instead of MRO liquidation.
Hypothetical math makes the working-capital issue visible. If a plant holds 200 unused PLC communication modules and fieldbus adapters at an average OEM replacement cost of $500 each, that is $100,000 in idle inventory. Even if only a portion is marketable, the audit can recover value while reducing clutter and cycle-count burden.
Consign: parts with a narrower but real buyer pool
Consignment fits slow-but-specific demand. Legacy fieldbus spares often have asymmetric demand. The buyer may not be searching every week, but when a line is down and distribution cannot supply the part, a documented module becomes valuable. That is why consign surplus DeviceNet modules, consign PROFIBUS I/O cards, and PLC communication module resale value are increasingly practical long-tail procurement searches.
For items with uncertain demand but strong part identity, consignment can be more appropriate than a bulk auction. Bulk lots tend to flatten value across mixed inventory. Consignment allows specific buyers to find specific surplus parts by catalog number, protocol, and condition.
For a broader framework on obsolete PLCs and related automation spares, see this guide to auditing, pricing, and consigning obsolete PLCs in 2026.
⚠️ Watch Out: Do not sell your last tested spare for an active legacy network. But do not let unneeded duplicates age into undocumented dead stock while other plants are still searching for the same part numbers.
Price Legacy Network Parts by Proof, Not Just Age
Resale pricing starts with confidence. Buyers of surplus automation equipment are not only buying a catalog number. They are buying confidence that the part is genuine, functional, compatible, and ready to install. That is especially true for fieldbus inventory, where a failed module can mean a stopped line and a rushed controls callout.
A practical pricing review should score each part across five dimensions:
- Identification: full catalog number, series, revision, firmware, voltage, network type, and accessory completeness.
- Condition: new sealed, new open box, used clean pull, used unknown, damaged, missing connector, or scrap-only.
- Test status: powered on, pulled from running equipment, bench-tested, configuration cleared, or untested.
- Installed-base relevance: still common in active plants, tied to a declining but meaningful architecture, or highly specialized.
- Migration timing: recently removed during Ethernet conversion, sitting for years without documentation, or still used as safety stock.
Condition categories should be strict. New old stock with intact packaging is not the same as a used module in a dusty bin. A clean pull from a working panel is not the same as an unverified part found during a warehouse cleanup. If you cannot prove condition, price conservatively or invest time in documentation before listing.
Protocol context also changes value. EtherNet/IP, PROFINET, and Modbus TCP are application protocols that share Ethernet cabling but differ in data exchange, configuration, and controller fit (Automation Distribution). That means the surplus market will not value every Ethernet-labeled device equally. A managed switch with PROFINET diagnostics, an EtherNet/IP bridge, and a Modbus TCP gateway may serve different buyers even if all sit on Ethernet infrastructure.
For legacy fieldbus parts, the strongest resale candidates are usually the items that solve a specific maintenance problem: discontinued communication processors, known-good scanners, gateway modules, remote I/O adapters, and specialty cards that keep existing systems alive through a phased migration.
Document before you list. Minimum listing data should include manufacturer, catalog number, series, firmware, condition, quantity, photos of labels and terminals, packaging status, and whether the part was removed from a working system. For gateways and switches, include protocol pairs, port count, power requirements, and whether the configuration has been cleared or backed up.
💸 Cost Reality: Age alone does not determine resale value. A documented, tested legacy communication module can outperform a newer but generic part if it solves an urgent installed-base problem.
What To Do Now
Use the Ethernet migration as the trigger for a focused MRO audit. Do not wait for the next full storeroom cleanup. The parts most likely to lose context are the ones pulled during controls upgrades, panel rebuilds, and phased network conversions.
- Pull a network-specific inventory export. Search your CMMS, ERP, crib system, and project leftover shelves for DeviceNet, ControlNet, PROFIBUS, Modbus RTU, Remote I/O, EtherNet/IP, PROFINET, EtherCAT, gateway, bridge, scanner, adapter, coupler, and communication module.
- Map each part to line status. Mark each item as active critical spare, active duplicate, migrated-line surplus, decommissioned-line surplus, or unknown. Require controls signoff before moving anything from critical spare to surplus.
- Package resale candidates by protocol and proof. Group DeviceNet modules separately from PROFIBUS cards, gateways separately from switches, and tested parts separately from untested inventory. Add photos, catalog numbers, series/revisions, and removal notes before seeking buyers.
🔑 Key Takeaway: The best time to sell surplus legacy fieldbus spare parts is after the migration creates excess, but before documentation, buyer demand, and internal ownership all decay.
If your 2026 Ethernet migration has left you with surplus DeviceNet, ControlNet, PROFIBUS, Remote I/O, gateways, switches, or PLC communication modules, Materialize can help you surface those parts to qualified industrial buyers through digital consignment. Start by listing your documented surplus at https://trymaterialize.com/sign-up.
