Single Pair Ethernet

What is Single Pair Ethernet?

Single Pair Ethernet (SPE) is a group of Ethernet physical layers in the IEEE 802.3 family that carry data, and optionally power, over a single twisted pair instead of the two or four pairs used by ordinary network cable. SPE started in the automotive industry, where every gram of copper matters, and has since become the foundation for Ethernet all the way to the sensor, the valve and the building controller. The key variants are 100BASE-T1 and 1000BASE-T1 for short distances and 10BASE-T1L, which delivers 10 Mbit/s over up to 1,000 metres and forms the physical layer underneath Ethernet-APL. This allows IP communication to take over from the 4-20 mA loop and traditional fieldbuses.

🧠 How does Single Pair Ethernet differ from standard Ethernet?

Standard copper Ethernet (100BASE-TX, 1000BASE-T) uses two or four pairs, RJ45 connectors and a maximum channel length of 100 metres. That suits an office well, but it is too bulky, too expensive and too short-range for a field instrument mounted somewhere in a plant or on a roof. SPE deliberately makes a different trade-off:

• One pair — thinner, lighter and cheaper cables and smaller connectors
• Full duplex over one pair — on point-to-point variants such as 10BASE-T1L and 1000BASE-T1, transmitting and receiving happen simultaneously over the same two conductors, with echo cancellation in the PHY; the 10BASE-T1S multidrop segment runs half duplex
• Power over the same conductors — with Power over Data Lines (PoDL), a sensor needs no separate power cable
• Reach or speed — each variant is optimised for one goal: long reach (10BASE-T1L), multidrop (10BASE-T1S) or high speed over short distances (1000BASE-T1)

Above the physical layer nothing changes: frames, MAC addresses, IP, TSN and industrial protocols work exactly as you would expect. For the fundamentals of frames and switching, see how Ethernet works.

🔧 Which IEEE standards define SPE?

10BASE-T1S stands out because several devices share one cable, much like a fieldbus. Collisions are avoided with PLCA (Physical Layer Collision Avoidance): a coordinator node sends a beacon, after which each node in turn gets a transmit opportunity. 100BASE-T1L is the newest addition; the standard was published in June 2026 and products have yet to become widely available.

🔌 Which connectors and cables does SPE use?

After years of competing proposals, the cabling committees ISO/IEC JTC 1/SC 25 and TIA TR-42 selected two mating faces from the IEC 63171 series, in a process launched in 2018 partly at the request of IEEE 802.3. IEEE 802.3 then adopted their recommendation:

• IEC 63171-1 — a compact LC-style connector proposed by CommScope, for office and building cabling (environmental class M1I1C1E1, IP20)
• IEC 63171-6 — the “T1 Industrial” interface proposed by HARTING and published in January 2020, for industrial environments (M2I2C2E2 and M3I3C3E3), from IP20 to IP65/67 and in M8 and M12 versions

Two industry groups are active around these choices. The SPE Industrial Partner Network, including HARTING and TE Connectivity, promotes the IEC 63171-6 mating face. The Single Pair Ethernet System Alliance, founded in 2020 by companies including R&M, Phoenix Contact, Weidmüller, Fluke Networks and Telegartner, focuses on a broad SPE ecosystem and also supports other mating faces such as IEC 63171-2 and -5. When procuring devices, always check which mating face they use.

For cabling, SPE channels have been added to ISO/IEC 11801-3 (2021 amendment) and TIA-568.5. Long 10BASE-T1L runs typically use shielded cable with heavier-gauge conductors, or reuse existing type A fieldbus cable as known from PROFIBUS PA.

⚡ How does power over Single Pair Ethernet work?

PoDL (Power over Data Lines) superimposes a DC voltage on the same pair that carries the data, with inductors and capacitors separating the two. IEEE 802.3bu defined classes 0 to 9 (0.5 to 50 W), mainly with vehicles in mind. IEEE 802.3cg added classes 10 to 15 for 10BASE-T1L, sometimes called SPoE:

For comparison, a 4-20 mA loop supplies an instrument with no more than a few tens of milliwatts. Hazardous areas follow separate rules: there, Ethernet-APL limits the energy using 2-WISE, based on the principle of intrinsic safety.

🔄 How does SPE compare with 4-20 mA, HART, IO-Link and Ethernet-APL?

Ethernet-APL is therefore not a competitor but a profile of SPE: it takes 10BASE-T1L and adds port profiles, power rules and explosion protection for the process industry. IO-Link remains strong for low-cost sensors close to the machine for now; SPE can provide the link from the IO-Link master to the control network.

🏭 Where is Single Pair Ethernet used?

• Process industry — through Ethernet-APL, transmitters, valves and analysers with 10BASE-T1L replace the 4-20 mA/HART loop and fieldbuses such as PROFIBUS PA and FOUNDATION Fieldbus
• Factory automation — sensors, small actuators and remote I/O with M8 or M12 connectors, without a gateway to a fieldbus
• Building automation — controllers for HVAC, heat pumps, lighting and access control over longer distances, replacing RS-485 buses
• Automotive — where it all began: 100BASE-T1 and 1000BASE-T1 for cameras, radar and control units in vehicles
• Brownfield upgrades — existing two-wire copper can often be reused, saving on trenching and cable pulling

The main benefit is “IP to the edge”: diagnostics, calibration data and process values are directly accessible via Industrial Ethernet protocols such as PROFINET, EtherNet/IP and OPC UA, with no translation in a gateway.

🔐 What does SPE mean for OT security?

Every SPE device is a full network node with its own IP stack. That is a functional gain, but it enlarges the attack surface at the lowest level of the installation, where until now only analogue signals travelled.

• More endpoints — hundreds of sensors become network nodes; add them to your asset inventory and track firmware versions
• Segmentation — place field devices in their own zones and conduits following network segmentation principles, and only allow the protocols needed towards the control level
• Device security — ask suppliers about certification against IEC 62443-4-2: authentication, signed firmware and services that can be disabled
• Port-level access control — managed industrial switches with port security or 802.1X stop anyone from quietly plugging a laptop into a field cable
• Shared medium on 10BASE-T1S — every node on a multidrop segment sees all traffic, so encryption or logical separation matters even more there

🛠️ How do you plan an SPE project step by step?

1. Choose the variant — 10BASE-T1L for long runs and process instruments, 10BASE-T1S for short multidrop buses, 1000BASE-T1 for cameras and high bandwidth; Ethernet-APL in hazardous areas
2. Survey the cabling — decide whether existing two-wire cabling can be reused, and measure cable length, conductor gauge and shielding
3. Standardise the mating face — IEC 63171-6 (M8/M12) for the plant floor, IEC 63171-1 for buildings; write this into your procurement specification
4. Calculate the power budget — which PoDL class does each device need, and how much power does the switch deliver per port and in total?
5. Design the network — switches with SPE ports, uplinks to the existing network, VLANs and zones, an addressing plan and time synchronisation
6. Build in security — asset registration, segmentation, firmware management and monitoring from the very first pilot, not as an afterthought
7. Start with a pilot — one measurement loop or one part of a building, including maintenance and troubleshooting by your own technicians

❓ Frequently asked questions

Is Single Pair Ethernet the same as Ethernet-APL?

No, Single Pair Ethernet is the umbrella term for Ethernet over one twisted pair, while Ethernet-APL is a specific profile of it for the process industry. Ethernet-APL uses the 10BASE-T1L variant of SPE and adds port profiles, power rules and intrinsic safety for hazardous areas. Every Ethernet-APL device therefore uses SPE, but not every SPE device is Ethernet-APL.

How far can Single Pair Ethernet reach?

The reach of Single Pair Ethernet depends on the variant. 10BASE-T1L covers up to 1,000 metres at 10 Mbit/s, 100BASE-T1L up to 500 metres, 10BASE-T1S around 25 metres in multidrop mode and 1000BASE-T1 a maximum of 40 metres. Standard four-pair Ethernet remains limited to 100 metres.

Can Single Pair Ethernet power a device?

Yes, Single Pair Ethernet can deliver power over the same pair using PoDL (Power over Data Lines). For 10BASE-T1L, IEEE 802.3cg defines classes 10 to 15, ranging from about 1.2 W to 52 W at the device. That is far more than a 4-20 mA loop provides and enough for smart sensors and small actuators.

Which connector does Single Pair Ethernet use in industry?

For industrial applications, IEC 63171-6 is the selected mating face for Single Pair Ethernet, available in IP20 and IP65/67 and in M8 and M12 versions. For office and building cabling, IEC 63171-1, a compact LC-style connector, was chosen. Other mating faces also exist, so always check the device specification.

Will Single Pair Ethernet replace 4-20 mA and HART?

Single Pair Ethernet can replace 4-20 mA and HART, but the transition is gradual. It is gaining ground in new process plants through Ethernet-APL, while existing installations will keep running analogue loops for decades. Many organisations therefore opt for a mixed architecture in which SPE is first deployed in new builds and extensions.

Is Single Pair Ethernet secure enough for critical installations?

Single Pair Ethernet itself contains no security; it is a physical layer that brings IP into the field. Security depends on segmentation, devices that comply with IEC 62443-4-2, managed switches and proper monitoring. With those measures in place, SPE can be secured as well as any other industrial Ethernet.

📌 In summary

Single Pair Ethernet brings IP communication and power over a single twisted pair to sensors and field devices, gradually replacing analogue loops and fieldbuses. 10BASE-T1L with its 1,000-metre reach and the industrial IEC 63171-6 connector form the core for industry, with Ethernet-APL as the profile for the process industry. In 2026 SPE is technically mature, but adoption is still cautious. Anyone getting started should treat every sensor from day one as a network device that must be inventoried, segmented and secured.