• • • CABLES & CONNECTORS • • •
Single Pair Ethernet – when two will do By Ben Morgan, Product Segment Leader for SPE connectors, Farnell
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ou can tell how successful a networking technology is by the way it evolves. For example, Ethernet is still being updated despite its basic principles being developed half a century ago. Its latest variant, Single Pair Ethernet (SPE), extends its reach into cars, factories, process industries and beyond.
The key innovation driving SPE’s uptake in these markets? Halving the number of conductors necessary in an Ethernet cable.
This simple change is having a profound effect on the utility of Ethernet. The earliest implementations of the standard used thick coaxial cables as the physical bearer. Eventually, Ethernet’s physical bearer evolved into the form we see today, up to eight conductors, each insulated and then twisted into pairs, all encapsulated into one, rather unwieldy sheath. This cable, usually grey, is seen in network racks across the world. However, the format has been less successful in penetrating industrial applications. This is becoming an issue as organisations implement Industrial Internet of Things (IIoT) strategies into their operations.
The promise of the IIoT is much smarter management of physical processes thanks to rich instrumentation enabled by widely distributed sensors, and enhanced control enabled by cloud-based analytics and distributed actuators. Each sensor and actuator needs a network connection and, in many cases, these connections have been implemented using a Tower of Babel of field networking standards, from CANbus through to Wi-Fi. Integrating sensors, actuators and cloud analytics has often involved using a hotchpotch of gateways and repeaters just to get the data to flow. In many cases, implementing an IIoT strategy has also meant distributing power feeds, compounding the cable routing issue.
What is SPE?
SPE, in its most basic form, is what its name implies; two conductors twisted together and encapsulated in a single thin, light, flexible cable sheath. Variants of the SPE standard (subsets of IEEE 802.3) offer trade-offs between data rates of up to 1Gbit/s, which is good for use in data-rich environments, and transmission distances of up to 1000m, which is good for use in large facilities.
There are also variants of the SPE standard that can deliver power to end nodes, using a strategy known as Power over Data Lines (PoDL). In its two-wire form, an SPE connection with a suitable driver can deliver up to 50W to an end node. (There is a variant of the standard that adds back another conductor pair to enable power delivery of up to 400W.)
SPE is evolving rapidly, but here are some of the more established variants of the standard
• 100BASE-T1 is designed for use in automotive environments over a single balanced twisted-pair cable and supports bidirectional data rates of up to 100Mbit/s over 15m, or up to 40m using shielded cables.
• 10BASE-T1S is a short-range variant of SPE that enables a multi-drop network topology, in which all the nodes are connected over one unshielded twisted pair cable of up to 25m long.
40 ELECTRICAL ENGINEERING • APRIL 2025
electricalengineeringmagazine.co.uk
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