Single Twisted-pair Ethernet (SPE)
The publication IEEE 802.3cg-2019 - IEEE Standard for Ethernet - Amendment 5: Physical Layer Specifications and Management Parameters for 10 Mb/s Operation and Associated Power Delivery over a Single Balanced Pair of Conductors enabled Ethernet long reach applications. The 10BASE-T1L variant allowed servicing such applications as industrial process control, building automation, webcameras, access control and sensors at a distance of up to 1 km and a speed of 10 MB/s. Being a power over data line system (PoDL) the remote terminals that are powered devices (PDs) can be powered with 20 W at 1 km and 52 W at 300 m.
Another popular name for 10BASE-T1L is single twisted-pair Ethernet (SPE). As only a single twisted pair is involved, both power and signal are on the same two conductors. Unlike power over Ethernet (PoE) the power sourcing equipment (PSE) Ethernet port is not necessarily floating or unearthed. Particular protection problems are the differential voltages of the local PSE and PD earths or protective earth (PE) and the normal PoE reach of 100 m is 10× further at 1 km with STE. Currently the industrial SPE connectors are to be employed with shielded cable, which will reduce the coupling of lightning and switching transients on long reach cables. In addition the shielding must be able to carry the high currents resulting from any differential earth voltages between the PSE and PD.
Thicker conductors (lower resistance) conductors than are used for PoE are necessary keep cable voltage drop to an acceptable value. The figure below shows how the PD delivered power depends on the link segment distance and the STE conductor AWG value.
At the Virtual ATIS PEG 2021 Webinar in February the topic of SPE will be more fully explored.