| Documents | ISO/IEC TS 29125, TIA TSB-184-A and CLC/TR 50174-99-1 |
| Subject | Cabling requirements and guidance for remote powering, including temperature rise in cable bundles |
| Publishers | ISO/IEC JTC 1/SC 25; TIA TR-42; CENELEC |
| Earlier editions | ISO/IEC TR 29125 and TIA TSB-184, cited in IEEE 802.3 Clause 33 |
Why bundles matter
Power over Ethernet sends DC current through the cable’s conductors, and the conductor resistance turns some of it into heat. A single cable sheds that heat easily. In a bundle, the cables in the middle are surrounded by other warm cables and run hotter. The higher the current, the bigger the bundle and the more enclosed the pathway, the greater the temperature rise.
Heat matters for two reasons: the cable must not exceed its temperature rating, and insertion loss increases with temperature, which shortens the maximum channel length.
The three documents
| Document | Title | Current edition | Status |
|---|---|---|---|
| ISO/IEC TS 29125 | Information technology. Telecommunications cabling requirements for remote powering of terminal equipment | 2017, with Amd 1:2020 and Amd 2:2024 (each with a 2025 corrigendum) | Current. CENELEC adopted the 2017 edition with Amd 1 as CLC ISO/IEC/TS 29125:2025; Amd 2 is not included |
| TIA TSB-184-A | Guidelines for supporting power delivery over balanced twisted-pair cabling | 2017, with Addendum 1 (2019, 28 AWG cords) and Addendum 2 (2024, single pair) | Current |
| CLC/TR 50174-99-1 | Information technology. Cabling installation. Part 99-1: Remote powering | 2015 (BSI: PD CLC/TR 50174-99-1:2015) | Listed as withdrawn in the CENELEC catalogue in 2026; still listed as current by BSI |
Temperature assumptions
| ISO/IEC TS 29125 | TIA TSB-184-A | |
|---|---|---|
| Cable temperature rating | As specified in the ISO/IEC 11801 series: up to 60 °C in MICE C1 environments, 70 °C in C2 and C3 (Amd 2 wording) | 60 °C |
| Ambient assumed | Up to 50 °C possible | 45 °C maximum |
| Temperature rise | Above 10 °C not recommended | Up to 15 °C |
| Current covered (four-pair) | Up to 500 mA per conductor (1 A per pair) | Up to 1000 mA per pair |
| Bundle size | Reinforces the ISO/IEC 14763-2 recommendation of no more than 24 cables per bundle | 24 cables per bundle in typical pathways (conduit or tray without insulation) |
The two documents use different assumptions, so their figures cannot be mixed. In every case, the cable must not exceed its temperature rating.
Example from ISO/IEC TS 29125
ISO/IEC TS 29125 Table 1 gives the maximum current per conductor for a 10 °C rise in a bundle of 37 cables with all four pairs energised:
| Cabling | In air | In conduit |
|---|---|---|
| Category 5 cable | 482 mA | 406 mA |
| Cords with 0.4 mm conductors | 393 mA | 315 mA |
For bundles suspended in air, the standard notes that, to allow for a 50 °C ambient and keep the rise to 10 °C, minimum Category 5 cables carrying 500 mA per conductor need bundles smaller than 100 cables.
Ways to reduce temperature rise
The measures listed in ISO/IEC TS 29125 include:
- a higher category of cable;
- larger conductors;
- a screen or other metallic elements in the cable;
- solid insulation;
- a larger cable diameter;
- energising fewer pairs;
- smaller or looser bundles;
- mixing powered and unpowered cables in a bundle.
Length de-rating for temperature
| Cable | 20 to 40 °C | Above 40 to 60 °C |
|---|---|---|
| Unscreened (U/UTP) | 0.4% per °C | 0.6% per °C |
| Screened | 0.2% per °C | 0.2% per °C |
ISO/IEC 11801 reduces the maximum length by these factors for each degree above 20 °C, and ISO/IEC TS 29125 says the same de-rating should be applied to powered links that run warm. TIA applies the same factors to insertion loss. Screened cables are less affected because their loss rises less with temperature.
Unplugging under load
| Standard | Test |
|---|---|
| IEC 60512-99-001:2012 | Test 99a: engaging and separating connectors under electrical load, for twisted-pair connectors with remote power |
| IEC 60512-99-002 (Ed. 2.0, 2022, with Amd 1:2025) | Test 99b: endurance schedule for unmating under electrical load, at least 100 operations |
| IEC 60512-99-003:2023 | Test 99c: the equivalent for IEC 63171 single-pair connectors |
Unplugging a powered link can cause a small arc at the contacts. ISO/IEC TS 29125 says removing power before disconnecting, through port power management, is the preferred approach.
For the power levels themselves, read PoE vs PoE+ vs PoE++.