Single-Pair Ethernet for Industrial Sensors — Why SPE Is Replacing the Sensor Cabling You Know

A controls engineer we work with put it this way last month:“I have spent twenty-five years pulling four-wire M12 cables to every sensor on every machine. Now my distributor tells me one twisted pair is going to replace them all. I want to believe it. I also want to know what is actually in a catalogue I can order from today.” That is the right question to ask, and the answer is more interesting than either the vendor pitch or the cynicism.

Single-Pair Ethernet — SPE — is genuinely the biggest shift in sensor cabling since the M12 connector itself. It is also a multi-year migration, not a flag day. This article is the version of the SPE conversation we have with engineers who are trying to plan around it: what the underlying standards actually say, what is shipping in 2026, where safety sensors fit, and when the migration story pays off on a real factory.

What SPE actually is, in plain terms

Classical industrial Ethernet at the field level — 100BASE-TX over Cat5e, 1000BASE-T over Cat6 — uses two or four twisted pairs in an eight-conductor cable terminated with RJ45 or M12 D/X-coded connectors. It works, but it is heavier, more expensive per metre, and harder to route in tight machinery than the two- or three-conductor cables that fieldbus and analog instrumentation have always used.

SPE collapses the physical layer back to one twisted pair while keeping Ethernet on top. That is the whole idea. The standards that matter for industrial sensors are:

• IEEE 802.3cg-2019 — the amendment that defined two new 10 Mbit/s SPE variants. 10BASE-T1L is the long-reach option, point-to-point, up to 1000 m on a single pair. 10BASE-T1S is the short-reach option, which supports multidrop topologies on a shared bus for shorter distances, with the PLCA (Physical Layer Collision Avoidance) mechanism handling deterministic media access.
• IEEE 802.3bu-2016 plus the PoDL clauses added by 802.3cg — Power over Data Lines, the SPE equivalent of PoE. Unlike classical PoE, which uses spare pairs or phantom power across two pairs, PoDL carries DC power on the same single pair as the data. The combined specification defines a set of power classes spanning roughly 0.5 W to about 50 W at the powered device, across nominal 12 V, 24 V and 48 V groups.
• 100BASE-T1 and 1000BASE-T1 — older SPE variants originating in automotive networking. They exist on factory floors too, particularly inside machines, but the 10 Mbit/s long-reach 10BASE-T1L is what is reshaping sensor cabling specifically, because the cable budget and reach match the way sensors are actually installed.

Notice what is not on that list: a new application protocol. SPE is a physical layer. PROFINET, EtherNet/IP, EtherCAT, Modbus/TCP and OPC UA all run unchanged on top of an SPE link, which is exactly why the major fieldbus organizations have embraced it rather than treating it as a competitor. SPE is the wire; the protocol stack you already use stays the same.

The connector politics — T1 Industrial, IEC 63171, and the still-unfinished consolidation

The single most confusing thing about SPE for a buyer in 2026 is the connector. Ethernet historically converged on RJ45 for office and M12 for industrial, and you could buy a cable without thinking. SPE has not converged. The IEC has standardized three different mating faces in the IEC 63171 family, and each has a different home market:

• IEC 63171-2 — originating from Reichle & De-Massari, targeting IP20 office, building automation and control-cabinet environments.
• IEC 63171-5 — an IP67 industrial extension of the -2 mating face, with Phoenix Contact and Weidmüller as the principal backers, aimed at harsh environments.
• IEC 63171-6 — the “T1 Industrial” interface developed by HARTING (the Tw1ster) and adopted by TE Connectivity, also IP67-rated and the variant most commonly seen on industrial sensor housings today.

All three are real standards with shipping product behind them. For sensor work on the factory floor, the -5 and -6 IP67 variants are the ones that matter, and a practical rule for 2026 is: pick one ecosystem, align your cables, panel feedthroughs, switches and sensor vendors to it, and stop worrying about the other. The SPE Industrial Partner Network — whose founding members include HARTING, TE Connectivity, HIROSE, Würth Elektronik, Bizlink, MURR Elektronik and Softing — has been the gravitational centre for the -6 ecosystem, and in 2025 it merged with the Single Pair Ethernet System Alliance to consolidate the broader SPE push.

SPE vs the cabling you already have

The clearest way to see what SPE changes is to put it next to the two cabling schemes it competes with on a sensor: the classical three- or four-wire 24 V DC sensor on M12, and a three-wire IO-Link sensor on M12 class A.

Read the table carefully and the message is not “SPE replaces everything tomorrow.” The message is that SPE finally puts a single physical layer in the row labelled “long runs, IP-native diagnostics, fewer wires” — a row that, until recently, no sensor cabling option really owned. Traditional M12 is still the cheapest answer for a simple on/off proximity switch one metre from a PLC. IO-Link is still the right choice today for parametrizable sensors at the last meter, including safety-rated IO-Link devices. SPE pulls ahead when distance, data, and diagnostic openness all matter on the same cable.

What SPE means for safety sensors specifically

The honest answer for safety sensors — light curtains, laser scanners, safety door interlocks, safety relays — is more nuanced than for general industrial sensors, and it is worth separating cleanly.

What SPE changes: the physical layer and the power delivery. A safety light curtain receiver with an SPE port is wired with one twisted pair carrying both Ethernet and PoDL power, instead of a multi-conductor M12 cable carrying 24 V plus two OSSD outputs. The cable is thinner, the conduit is lighter, the connectorization is faster, and the 1000 m reach of 10BASE-T1L makes long perimeter runs — fence-mounted scanners, area-protection curtains across a large cell — far easier than dragging shielded multi-conductor cable.

What SPE does not change: the safety architecture. A safety light curtain is still a Type 2 or Type 4 device per IEC 61496, still has to be evaluated as part of a safety function up to PL e / SIL 3 per ISO 13849 / IEC 62061, and still has to deliver its safe state to a certified safety logic device. Today, that means an OSSD pair into a safety relay or safety PLC. When safety-rated SPE protocols mature, the same device will deliver its safe state over a safety protocol on the SPE link — but the safety logic, the dual-channel evaluation, and the certified controller all remain part of the picture. SPE removes wires; it does not remove safety architecture. If anyone tells you otherwise, push back. The same point we made in our companion piece on connecting light curtains to PLCs applies: the cable is the easy part of the safety function.

IO-Link, IO-Link Safety, and where SPE intersects them

IO-Link has spent the last decade becoming the dominant last-meter sensor protocol in factory automation, and IO-Link Safety added a certified safety profile on top of the same three-wire physical layer. So a fair question is whether SPE eats IO-Link, or vice versa, or whether they coexist.

The answer in 2026 is coexistence, with a slow migration. PROFIBUS & PROFINET International and the IO-Link Consortium have published concept work on running IO-Link over SPE, and an IO-Link over SPE working group is active. Standard (non-safety) IO-Link over SPE is the closer milestone; IO-Link Safety over SPE is further out and not generally available as a finalized specification at the time of writing. In parallel, SPE Media Switches from suppliers such as Hilscher already act as bridges between SPE field segments and PROFINET, EtherNet/IP and Modbus/TCP backbones, which means an early-adopter plant can install SPE-native sensors today without rebuilding its controls backbone.

For a project that genuinely needs functional safety on a serial bus today, classical IO-Link Safety on its proven three-wire interface is still the right answer. SPE is a forward bet, not a present-day safety replacement.

What is actually shipping in 2026

A reasonable summary of the 2026 catalogue, sector by sector:

• Process instrumentation — this is where SPE is furthest along. Endress+Hauser, Siemens and other process-automation suppliers have shipped 10BASE-T1L-capable field instruments aimed at the long-reach replacement of HART and 4-20 mA loops. The 1000 m reach is the headline feature, because chemical plants and refineries routinely have field instruments hundreds of metres from a marshalling cabinet.
• Standard factory sensors — SPE variants of inductive, photoelectric and RFID devices are appearing as product studies and early commercial parts rather than as full mainstream catalogues. Pepperl+Fuchs, for example, has publicly presented SPE-equipped RFID product studies at SPS 2025, and other major sensor vendors are following at a similar pace. The shape of the market in 2026 is “available if you ask for it,” not “default on every page of the catalogue.”
• Safety sensors — safety-rated devices with an SPE interface are the rearmost cohort of the migration. Safety architectures are conservative for good reasons, certification cycles for new physical layers are long, and a safety-rated SPE protocol stack is still settling. Plan for safety-SPE sensors to mature later this decade, not this quarter.
• Infrastructure — SPE switches, media converters and PoDL power sourcing equipment from Hilscher, HARTING, Phoenix Contact and others are available today, which is what makes pilots possible.

When does the migration pay off?

The SPE business case is not the cable. A pair of conductors is cheaper than four, but not by enough to retrofit a plant. The case is everything around the cable: fewer terminations, smaller cable trays, smaller panels because remote I/O can live in the field, fewer protocol-conversion gateways (HART-to-Ethernet, fieldbus-to-Ethernet) because IP-native devices speak directly to your controls layer, and richer diagnostics because every sensor has its own MAC address and can be queried with the same tooling as the rest of the network.

That payoff is concentrated in new builds. The three project shapes where SPE is genuinely a 2026-grade choice are:

• Process plants and large skids with long runs from field instrumentation to marshalling, where 10BASE-T1L's reach replaces both 4-20 mA loops and HART gateways at once.
• Greenfield factory automation cells being specified now for production in 2027 and beyond, where SPE-native sensors and switches can be selected from the start instead of bolted on later.
• Distributed perimeter and area protection applications — large fence lines, wide entrance curtains, scattered scanners around a complex cell — where the SPE reach genuinely shortens the cable tray and removes intermediate junction boxes.

Conversely, ripping out working M12 cordsets on a running line to chase a thinner cable is rarely justified. Treat the existing fleet as a sunk asset; treat SPE as the default for the next thing you build.

A short list of things to get right before you commit

• Pick a connector family and stick to it. IEC 63171-5 or IEC 63171-6 for industrial. Mixing both on one plant is a spare-parts nightmare.
• Verify the PoDL class on every device. The PoDL class on the sensor must be supported by the power sourcing equipment; mismatches lead to under-powered devices that look like intermittent network faults.
• Plan the migration of safety functions separately. Standard SPE sensors can move faster than safety-rated ones. Do not let an enthusiastic pilot push safety devices onto an uncertified path.
• Test cable lengths in the actual environment. 10BASE-T1L is rated to 1000 m on cable that meets the standard, but in heavy-EMI environments a real-world test with the cable you intend to install is worth a week of theoretical argument.
• Treat SPE switches and media converters as controls infrastructure. They need the same change control, firmware management, and lifecycle planning as your PROFINET or EtherNet/IP gear.

Where DAIDISIKE fits — honestly

A straight answer, since you are reading this on a sensor manufacturer's site. DAIDISIKE has built safety light curtains, safety laser scanners and safety relays for nearly two decades, with customers including BYD, Huawei, Midea, Foxconn and Samsung. The DQA, DQC, DQT4, DQE, DQO, DQSA, DQR, MK and JER curtain families, the DLD-series industrial LiDAR scanners, the DA31 safety relay and the DX-series safety door locks all ship today on the cabling the industry actually uses — M12, terminal blocks, OSSD outputs to safety relays and safety PLCs.

We are watching the SPE ecosystem closely, and we expect the long-reach 10BASE-T1L story to be especially relevant for our area-protection curtains and LiDAR scanners, where customers already ask about long runs and integrated diagnostics. What we will not do is rush a safety-rated SPE interface to market ahead of the certification work. When SPE-native safety devices are right, they will be right; until then, our job is to keep delivering Type 2 and Type 4 light curtains, safety scanners and the surrounding logic on the proven cabling that gets a line audited, signed off, and into production.

The bottom line

Single-Pair Ethernet is the most significant change to industrial sensor cabling in thirty years, and it is real. IEEE 802.3cg-2019 defined the physical layer, PoDL handles the power, the IEC 63171 connector family is settling around two industrial mating faces, and a 50-plus member SPE Industrial Partner Network has consolidated the industrial push. Process instrumentation has moved first; standard factory sensors are following in 2025 and 2026; safety sensors will move later in the decade as safety-rated SPE protocols mature.

For a controls engineer in 2026, the right posture is neither rip-and-replace nor wait-and-see. It is: keep buying the cabling that works for the line you are running today, pilot SPE on the next greenfield project where its reach and diagnostics genuinely earn it, and let your sensor vendors tell you when the safety side has caught up. The cable will come; the standards are already there. The discipline is in getting the timing right.