SPE-cabling, is an ethernet cabling design that uses only a single pair of wires to transmit data, in contrast to the two/four wire pair Ethernet configurations. There are three forces driving SPE deployment:
- Whilst 4-20 mA current loop has been the prevailing process control signal in many industries thanks to its robustness and simplicity, it is no longer adequate for future digital tasks.
- The desire to reduce weight, cost, and footprint, in applications in which potentially lower transfer speeds do not cause drawbacks, such as in industrial applications, Single-Pair Ethernet (SPE) provides significant economic, density, sustainability, and installation advantages.
- The convergence of operational technology (OT) and information technology (IT), also known as Industry 4.0. The various networks need to “talk” to each other and therefore Ethernet-based communications are migrating further down in the automation hierarchy. In some cases, right down to the smart sensors on the plant floor which typically do not require a lot of power and have low bandwidth requirements.
Experts also consider Ethernet to be more consistent, more efficient, and more cost-effective than fieldbus systems.
Four-pair and single-pair wiring solutions will in many cases coexist in support of the same application. Single-pair Ethernet can be used to connect the sensors and actuators to the nearest consolidation point, and four-pair cabling can link the consolidation point and control room.
STANDARDS
Standards bodies have ramped up the development of guidelines for a variety of applications involving single-pair cabling, as well as the components used in its deployment.
For example, the upcoming ISO/IEC 11801-1 Amd.1, contains changes and additions to the published version that specify three new categories of single-pair components and the three new classes of channels and links to support single-pair applications. There is similar content in amendment ANSI/TIA 568.5-1, although in this case the standard only specifies one new category.
Keep in mind that these premise documents lead to the planning and installation standard ISO/IEC 14763-2. In addition, anyone looking at remote powering may also want to look at ISO/IEC TS 29125, which discusses heating rise and building concerns when using data cabling for applications such as Power over Ethernet (PoE). Both these documents are being updated to cover the new higher current power levels offered by Single Pair Ethernet.
ISO/IEC 11801-9911, which is due for publication in 2024, will be relevant for those considering the use of existing classes of four pair cabling to act as cable sharing channels for proposed future single-pair applications.
CONCLUSION
Since the launch of Cat.8, cabling standards have been stable for four pair applications, but there have been a lot of updates on single-pair components and test techniques. As of the date of this article, June 2023, much of this has recently been published or is pending imminent publication.