Fibre Cable Power Loss Calculations

When having fiber optic cables tested for power loss, make sure the pass/fail limit is determined from a cable loss calculation rather than a simple 5 db limit.

Calculating loss limits based on a building-cabling standard

Using TIA/EIA568 as an example, calculate the loss limit at 850nm for a 62.5mm fiber cable that is 127m long. The cable has a connector on each end of the permanent link with one splice. In the TIA/EIA568 standard, the following maximum loss values are given:

In order to meet the requirements of the TIA/EIA568 installation standard, the test limit for a 127m cable should be 2.28 dB or less. Any power loss measurement beyond 2.28 dB for this link indicates an installation does not in conform to the TIA/EIA568 standard.

Conclusion

Do not accept a Power Loss Reading without a calculated Power Loss Limit. It is no longer acceptable to consider a result that is less than 5 dB as ok" even if the network still runs, especially as network speeds increase to 100 Mbps and beyond. Always demand a calculated Power Loss Limit for each power loss measurement in your fiber optic network so you can ensure the installation is performed to required industry standards.

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Last modified: 04 June 2005