What Is 10BASE-T1L?

10BASE-T1L is the long-reach single pair Ethernet (SPE) physical layer from the IEEE 802.3cg amendment, published in 2019. It sends 10 Mb/s in both directions at once over a single twisted pair, point to point, for up to 1,000 m. Standard Ethernet over twisted pair, by contrast, stops at 100 m and needs at least two pairs.

That reach is the point. Process plants, water networks, buildings and outdoor sites have thousands of sensors and actuators wired with long single-pair cables, traditionally carrying 4–20 mA current loops, HART or RS-485 fieldbuses. 10BASE-T1L lets those devices speak Ethernet and IP directly, so a pressure transmitter 800 m from the control room can be reached like any other networked device, with no gateway in between.

The 10 Mb/s rate looks slow next to gigabit Ethernet, but it is thousands of times faster than HART and plenty for field instruments, configuration data and diagnostics.

10BASE-T1L gets its reach from a slow, efficient line code. Data is mapped with 4B3T coding onto three voltage levels (PAM-3) at 7.5 MBd, which keeps the signal’s frequency content low enough to survive long, lossy cable. Echo cancellation lets both ends transmit on the same pair at once, so the link is full duplex.

The standard defines two transmit levels. The 2.4 V peak-to-peak level is for the full 1,000 m reach in ordinary areas. The 1.0 V level puts less energy on the cable, which suits intrinsically safe designs in hazardous areas, and is typically used on shorter runs. Long runs typically use a shielded twisted pair of around 18 AWG, and in many cases existing fieldbus cable can be reused after testing, which is a large part of the appeal on brownfield sites.

802.3cg also added power classes for single pair Ethernet, often called single pair Power over Ethernet (SPoE). Classes 10 to 15 build on the Power over Data Lines (PoDL) scheme from IEEE 802.3bu and deliver roughly 1 W to 50 W at the device, depending on class and cable length, on the same pair as the data. Coupling networks at each end keep the DC supply and the data signal apart.

Intrinsically safe field devices draw far less, and their power is limited by the hazardous-area rules rather than the Ethernet classes. Ethernet-APL, the process-industry profile built on 10BASE-T1L, defines its own power and protection rules for that case, and our FAQ on ATEX explains the hazardous-area background.

The long reach makes it a fit wherever field devices sit far from the network.

A 10BASE-T1L field device connects to a switch with T1L ports, which bridges it onto the plant’s standard Ethernet. From there its data travels like any other traffic to SCADA servers, historians and edge computers, using protocols such as OPC UA, Modbus TCP or EtherNet/IP. Connectors for industrial SPE follow the IEC 63171 family, including M8 and M12 circular versions sealed to IP67.

The practical gain shows up in maintenance. Because each instrument is now an IP device, engineers can read its diagnostics, change its configuration and update its firmware from the control room instead of walking out with a handheld communicator. Asset management and condition monitoring software can poll the same devices directly, and the network itself can be monitored with ordinary Ethernet tools such as SNMP and LLDP.

Our white paper on single pair Ethernet in industrial and edge AI computing compares 10BASE-T1L with the short-reach and automotive variants and covers connectors in more detail. For the serial networks that 10BASE-T1L often replaces in buildings, see our explainer on RS-485.

Where a project brings 10BASE-T1L data into the control room, we build the industrial computers that collect and process it as standard, with the protocol software set up before the system ships.