Ethernet Cable Length & Channel Calculator
Also known as Structured Cabling Channel Planner
The maximum length of a twisted-pair run, de-rated for cords and temperature, with the Ethernet speeds it will carry.
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Worked example: 10 m of 26 AWG cords at 50 °C
Maximum horizontal cable: 74.8 m
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How it works
Maximum Ethernet cable length: the 90 m plus 10 m rule
A twisted-pair channel is the whole run from the switch port to the device, at most 100 m. It is the fixed horizontal cable, the permanent link, at most 90 m, plus the patch, equipment and work area cords. The limits are a loss budget set by ISO/IEC 11801 and AS/NZS 11801.1, so anything that adds loss shortens the horizontal cable.
Stranded cords lose more per metre than solid cable. Past 10 m of 24 AWG cord, each extra metre of cord costs 1.2 m of horizontal cable, and with 26 AWG cord the trade starts at 8 m and costs 1.5 m (ANSI/TIA-568.1-D). Heat raises the loss too, so above 20 °C ISO/IEC 11801:2011 Table 32 shortens the horizontal cable by 0.2 % per degree if it is screened, and by 0.4 % per degree to 40 °C, then 0.6 % per degree to 60 °C, if it is unscreened. The cords are not de-rated.
Channel = H + C ≤ 100 m
H₂₀ = min(90, 102 − (1 + D) × C)
Hmax = H₂₀ × (1 − δ)
δ = 0.002 × (T − 20), screened
δ = 0.004 × (T − 20) to 40 °C, then 0.08 + 0.006 × (T − 40), unscreened
- H
- fixed horizontal cable, the permanent link, in metres
- C
- total length of the patch, equipment and work area cords, in metres
- D
- cord de-rating factor, 0.2 for 24 AWG cords and 0.5 for 26 AWG
- T
- operating temperature of the horizontal cable, 20 to 60 °C
- δ
- fraction of the horizontal length taken off for temperature
- H₂₀, Hmax
- maximum horizontal length at 20 °C and at the operating temperature, in metres. For Cat 8 the caps of 100 m and 90 m are 30 m and 24 m
Standards
- AS/NZS 11801.1 and ISO/IEC 11801-1 generic cabling: channel and permanent link length model
- ISO/IEC 11801:2011 Table 32, as reproduced by Fluke Networks (temperature de-rating of the horizontal cable; the edition before ISO/IEC 11801 was split into parts in 2017)
- ANSI/TIA-568-C.2 Annex G, as reproduced by Fluke Networks (its de-rating table differs from ISO: 75.0 m unscreened at 60 °C, where ISO gives 72.0 m; the planner follows ISO)
- ANSI/TIA-568.1-D multi-user telecommunications outlet cord table, C = (102 − H) / (1 + D), as reproduced in the Anixter Standards Reference Guide (cord length trade)
- ANSI/TIA-568.2-D channel limits, as reproduced in the Anixter Standards Reference Guide (555 ns propagation delay, 179.4 ns for Cat 8, 50 ns delay skew, channel insertion loss)
- AS/CA S009:2020 Appendix L (90 m horizontal rule, with a reference to AS/NZS 11801.1 for length restrictions due to heat and application)
- TIA TSB-155 (10GBASE-T over installed Cat 6: should operate to 37 m, and from 37 to 55 m depending on alien crosstalk)
- TIA TSB-184-A (PoE cable bundle temperature rise)
- ISO/IEC 11801 channel insertion loss model as broken down in IEEE 802.3an
- IEEE 802.3 BASE-T applications and PoE types
Worked example
Worked example: 10 m of 26 AWG cords at 50 °C
An unscreened Cat 6A run through a roof space that reaches 50 °C, with 10 m of 26 AWG patch, equipment and work area cords in total.
| Step | Working | Result |
|---|---|---|
| Cord trade | 102 − (1 + 0.5) × 10 | 87.0 m |
| Limit at 20 °C | smaller of 90 and 87.0 | 87.0 m |
| Temperature de-rating | 0.4 % × 20 + 0.6 % × 10 | 14.0 % |
| Maximum horizontal cable | 87.0 × (1 − 0.140) | 74.8 m |
The channel is then at most 84.8 m, the 74.8 m of horizontal cable plus the 10 m of cords. With 24 AWG cords the same 10 m leaves the full 90 m at 20 °C, which is the 90 m plus 10 m rule, and screened cable loses 6.0 % at 50 °C rather than 14.0 %.
What is the difference between a permanent link and a channel?
The permanent link is the fixed part of the run, the horizontal cable and its connectors, with a reference maximum of 90 m. The channel is the full end-to-end connection including the patch, equipment and work area cords, with a reference maximum of 100 m. The planner reports both against their limits.
Why is Ethernet limited to 100 metres?
The 100 m belongs to the cabling standard rather than to Ethernet, and it is a loss budget more than a distance. ISO/IEC 11801 sets the channel limits, such as insertion loss and propagation delay, for a reference channel of 100 m: 90 m of solid horizontal cable plus 10 m of cords, with four connections. The IEEE 802.3 BASE-T applications are designed to work over a channel that meets those limits, so long cords and a hot ceiling shorten the run as well as extra length.
Why does the maximum length fall with temperature?
Insertion loss in twisted-pair cable rises with temperature, so a run that passes at the 20 °C reference can fail when it is hot. ISO/IEC 11801:2011 (Table 32) reduces the horizontal cable by 0.2 % per degree above 20 °C for screened cable, and by 0.4 % per degree to 40 °C then 0.6 % per degree to 60 °C for unscreened cable. The cords are not reduced. The planner applies those factors up to 60 °C. ANSI/TIA-568-C.2 Annex G tabulates slightly different lengths, and the planner follows ISO.
Which Ethernet speeds can each category carry?
An application within a category's bandwidth reaches the full 100 m channel, so 1000BASE-T and 2.5GBASE-T run on Cat 5e and 10GBASE-T runs to 100 m on Cat 6A. 10GBASE-T over Cat 6 has a reduced reach: TIA TSB-155 says it should operate to 37 m, and from 37 to 55 m depending on the alien crosstalk environment, so the planner uses 37 m. 25GBASE-T and 40GBASE-T run on Cat 8 to 30 m. The planner lists each application with its reach for the chosen category.
How does this relate to AS/CA S009?
AS/CA S009:2020, the Australian Wiring Rules, gives the 90 m horizontal rule in Appendix L and refers to AS/NZS 11801.1 for further length restrictions due to heat and application. S009 does not itself carry the de-rating tables, so the planner's length model follows AS/NZS 11801.1 and ISO/IEC 11801, with the temperature de-rating from ISO/IEC 11801:2011 Table 32. ANSI/TIA-568-C.2 Annex G tabulates slightly different de-rated lengths, and the planner follows ISO.
Does this tool certify a cabling link?
No. Certification is a frequency swept measurement of insertion loss, NEXT, return loss and related parameters on the installed cable, done with a field tester. The planner is a design tool that checks lengths, de-rating, application reach and PoE, and it does not model NEXT, return loss or alien crosstalk.
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