On July 31, 2026 in Automation, Industrial, Industrial Automation, IoT by Abhishek Jadhav

SPE reduces cabling while extending Ethernet connectivity, bandwidth, and power delivery to industrial field devices

Ethernet has been one of the most important communication standards in industrial automation for connecting controllers, machine vision systems, control cabinets, supervisory platforms, and enterprise networks. It has standardized interfaces, high data rates, protocol interoperability, and a mature ecosystem for increasingly data-intensive automation architectures.

But standard multi-pair Ethernet does not scale efficiently to industrial field devices such as sensors, actuators, and distributed input/output (I/O) modules. Moreover, the deployment of four-pair cable assemblies can become too large, costly, and mechanically inflexible (Figure 1). Cable volume and bend-radius constraints also become significant when hundreds or thousands of field devices are installed.

Previously, we examined how Time-Sensitive Networking (TSN) enables predictable, low-latency communication across converged industrial Ethernet networks. In this blog, we dig into how Single Pair Ethernet (SPE) aims to address the constraints of traditional Ethernet by providing the same capabilities without the size, wiring complexity, and installation cost of conventional multi-pair physical media. SPE uses a single balanced pair of copper wires and offers optional power delivery for constrained industrial networks.

What Is Single Pair Ethernet?

SPE maintains the standard Ethernet frame format and the higher layers of the Open Systems Interconnection (OSI) model while simplifying the physical medium. It uses advanced modulation and echo cancellation to achieve full-duplex communication on two wires. This communication protocol provides several advantages for industrial engineers:

• Reduction of passive components: SPE reduces the wire count from eight to two for thinner, lighter, and more flexible cables.
• Simplified PCB design: SPE transceivers, or physical layer (PHY) devices, require fewer pins and smaller magnetics than multi-pair PHY devices, enabling compact device designs.
• Cable reuse potential: For some 10BASE-T1L retrofit applications, SPE can be implemented over existing twisted-pair fieldbus cabling (such as Type A fieldbus cable) if the cable meets basic impedance and attenuation requirements.

SPE Standards

The successful deployment of SPE depends on comprehensive standards. The IEEE 802.3 committee has developed a range of SPE physical layer specifications, each designed to meet specific industrial automation requirements.

These standards define data rates, transmission distances, signaling schemes, and network topologies. A key SPE amendment for industrial automation is IEEE 802.3cg-2019, which defines two different 10Mb/s PHYs: 10BASE-T1L and 10BASE-T1S.

10BASE-T1L Ethernet

10BASE-T1L is designed for long-range, point-to-point communication that can transmit full-duplex 10Mb/s Ethernet data over distances of up to 1,000m. This capability is important in process automation industries where facilities require long cable runs between field instrumentation and control rooms.

This standard provides an Ethernet-based migration path for installations that currently use legacy 4mA to 20mA analog loops and fieldbuses such as PROFIBUS PA and Foundation Fieldbus. This eliminates the requirement for protocol gateways and enables direct IP connectivity to industrial field devices.

10BASE-T1L uses a three-level pulse amplitude modulation (PAM3) scheme at a 7.5 megabaud (MBd) symbol rate. It has two transmit amplitude modes: a standard 1.0V peak-to-peak (Vpp) for most links and an optional 2.4Vpp level that can be auto-negotiated to overcome signal attenuation.

10BASE-T1S Ethernet

10BASE-T1S is optimized for short-range, multidrop applications. It uses a bus topology in which eight nodes share a single cable segment up to 25m long. This architecture is ideal for high-density applications, such as machine control cabinets and distributed I/O systems.

Even though 10Mb/s is sufficient for most field devices, higher bandwidth is sometimes required for machine vision and advanced sensor fusion applications. IEEE 802.3bw (100BASE-T1) provides 100Mb/s full-duplex communication over a single twisted pair with a reach of up to 15m on an unshielded cable.

For applications requiring gigabit bandwidth, IEEE 802.3bp defines 1000BASE-T1 to provide full-duplex 1Gb/s communication. This standard has an optional Type B link segment that supports at least 40m of reach and up to four inline connectors that extend SPE reach to industrial automation networks.

At the highest end of the performance spectrum is IEEE 802.3ch, which defines multi-gigabit SPE for 2.5Gb/s, 5Gb/s, and 10Gb/s, but its 15m reach limits its industrial application to short-distance, high-bandwidth scenarios. An example application includes connecting a vision sensor to its processor on a robotic arm.

Enhancing SPE with PoDL

One optional capability of SPE is to deliver electrical power simultaneously with data over the same two wires. Power over Data Lines (PoDL) is the technology enabling such an approach, and it was standardized in IEEE 802.3bu-2016 and further expanded in subsequent amendments of IEEE 802.3cg. Similarly, Single Pair Power over Ethernet (SPoE) delivers power and data over the same single balanced pair used for SPE transmission.

PoDL is the functional equivalent of Power over Ethernet (PoE) for the two-wire connection. The operation of PoDL is controlled by a complex, safety-oriented protocol that manages the interaction between the power sourcing equipment (PSE) supplying power (e.g., an SPE switch) and the power delivery (PD) device consuming the power (e.g., a field sensor).

Before supplying substantial power to the line, PSE performs a detection sequence to verify that a PoDL-compliant PD is connected to the network. This prevents the PSE from supplying power to a device that is not designed to receive it. After successful detection, the PSE proceeds to an optional classification phase using the Serial Communication Classification Protocol (SCCP).

This is a low-speed, bidirectional communication process that allows the PD to communicate with the PSE for its specific power requirements. The PSE then allocates and delivers the necessary voltage and current to optimize power management across the industrial network. Overall, the entire process ensures safe startup, continuous operation, and protection against fault conditions like short circuits.

Conclusion

SPE offers a compelling alternative to traditional fieldbus and multi-pair Ethernet systems. Combining reduced wiring, flexible installation options, standardized communication, and integrated power delivery, SPE helps streamline the transition toward more connected and data-rich industrial environments. Through standards such as 10BASE-T1L and 10BASE-T1S, SPE supports a wide range of industrial applications, from long-distance process instrumentation to short-reach multidrop networks. When paired with PoDL, it can also deliver power and data over the same cable, reducing infrastructure complexity while enabling direct connectivity to field devices.

In the last installation of this industrial networking blog series, we turn our attention to Message Queuing Telemetry Transport (MQTT) and the ways it is advancing Industrial Internet of Things (IIoT) communications.