| Full title | 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 |
| Publisher | IEEE Standards Association, IEEE 802.3 Ethernet Working Group |
| Approved | 7 November 2019, as an amendment to IEEE 802.3-2018 |
| Current home | Incorporated in IEEE 802.3-2022 (active edition) |
| Related standards | IEEE 802.3bu (PoDL), IEC 63171 series (single-pair connectors), ISO/IEC 11801-1, BS EN 50173-1 |
What it covers
IEEE 802.3cg adds two 10 Mb/s Ethernet physical layers that run over a single balanced pair of conductors, with optional power over the same pair. It is one of the single pair Ethernet (SPE) amendments to IEEE 802.3.
Target applications include industrial and process control, building automation trunks and spurs, lifts, fire alarm signalling loops, HVAC control, vehicles, and control-plane links inside equipment. In many of these, 10 Mb/s Ethernet over one pair replaces fieldbus or serial links.
Structure
| Clause in IEEE 802.3 | Content |
|---|---|
| Clause 146 | 10BASE-T1L: long reach, full duplex, point to point |
| Clause 147 | 10BASE-T1S: short reach. Half duplex point to point, with optional full duplex point to point, or optional half duplex multidrop |
| Clause 148 | PLCA (Physical Layer Collision Avoidance) Reconciliation Sublayer, used with 10BASE-T1S |
| Clause 104 | Power over Data Lines (PoDL), extended by 802.3cg |
| Clause 98 | Auto-negotiation for single-pair PHYs, extended for 10BASE-T1L |
Key technical parameters
| Parameter | 10BASE-T1L | 10BASE-T1S |
|---|---|---|
| Reach | 1 km (1000 m on 18 AWG cable) | 15 m point to point; 25 m multidrop mixing segment |
| Topology | Point to point | Point to point, or multidrop with at least 8 nodes on a linear segment with stubs |
| Duplex | Full | Half (full duplex optional on point-to-point links; multidrop is half duplex only) |
| Coding | 4B3T, PAM-3 | 4B/5B with DME |
| Symbol rate | 7.5 MBd | 12.5 MBd |
| Transmit amplitude | 1.0 V p-p, optional 2.4 V p-p (negotiated) | 1.0 V p-p |
| Cable assumed in reach figures | 18 AWG single balanced pair | 24 to 26 AWG single balanced pair |
Repeaters are not specified. For normative limits, check IEEE 802.3-2022 Clauses 146 and 147.
Power over the data pair
Power delivery over one pair is defined in Clause 104, Power over Data Lines (PoDL). It was first added by IEEE 802.3bu-2016, Amendment 8 to IEEE 802.3-2015, for single balanced twisted-pair Ethernet.
IEEE 802.3cg extended Clause 104 for the longer and more varied links of 10BASE-T1L and 10BASE-T1S. It allows loop resistance above the original 6.5 ohms, adds measurement of cable resistance so delivered power can be optimised, and adds further power classes.
PoDL is separate from PoE over two or four pairs (IEEE 802.3af, 802.3at and 802.3bt). The two are not interchangeable.
Connectors and cabling
IEEE 802.3 does not define the connector itself. Connectors for single-pair links are standardised by IEC SC 48B in the IEC 63171 series.
| Document | Content |
|---|---|
| IEC 63171:2025 (edition 2.0) | General requirements and tests for shielded or unshielded single-pair connectors with current-carrying capacity, including signal integrity requirements for the series |
| IEC 63171-1:2024 (edition 2.0) | Type 1, copper LC style, two-way connector. Rated to 600 MHz and 2.0 A at 60 °C. |
| IEC 63171-6:2021 (edition 2.0) | Shielded 2-way and 4-way (data/power) free and fixed connectors for data transmission up to 600 MHz |
What it means in practice
- Check which PHY the equipment uses. 10BASE-T1L and 10BASE-T1S are not interoperable with each other or with four-pair Ethernet without a converter or switch.
- For 10BASE-T1L runs near 1 km, the cable must support the reach. The 1 km figure assumes 18 AWG conductors.
- On 10BASE-T1S multidrop segments, check the maximum segment length, node count and stub lengths given by the equipment.
- Where power is needed, confirm that both ends support PoDL and the same power class.
- Specify the connector by its IEC 63171 part number to avoid mismatched mating faces.
Related reading: Industrial Ethernet protocols explained · Industrial connectivity: M12 connectors and cable for harsh environments.