KNOW HOW
Sin Five : Exceeding the bend radius
All fibre cables have a minimum bend radius . Users should take care to never exceed that radius to avoid damaging the cable and the fibres inside of it . When the bend in the cable exceeds the rated minimum , the fibres within suffer a type of damage called ‘ macro bending ’.
Macro bending occurs when cable slack loops are wound too tightly and placed in a pedestal , hand hole or vault that is too small for the cable diameter in underground OSP networks . Products like ‘ snow shoes ’ are designed to help fibre installers avoid macro bending of their aerial slack loops . Macro bending is common occurrence when an installer ‘ mouse ears ’ the slack loop and uses zip ties to secure to the aerial plant .
Macro bending of the fibres can also occur in the splice trays . A common scenario is when small splice trays are used in combination with 60mm splice sleeves , rather than the proper 40mm splice sleeves . The larger splice sleeves will be too close to the edge of the splice tray and will not allow for a sufficient bend radius .
Macro bends are often missed unless the network is tested at the 1,550nm or 1,625nm frequencies . Most single mode systems operate at 1,310nm because this wavelength is less sensitive to bends and other issues . However , more and more applications today also are using 1,550nm and 1,625nm . Here is the concern : These wavelengths are more sensitive to fibre aberrations . So at the 1,310nm wavelength operators may see nothing odd on the OTDR screen but at 1,550nm they may see something that resembles the Grand Canyon .
External pinching force
Cladding region
Fibre core
Inserting into fusion splicer .
Fibre core
Cladding region
Signal exceeds the critical angle and bleeds into cladding region
Avoid excessive bending and these problems fade away .
Sin Six : Hang on to those dirty wipes
It ’ s laudable the effort employees will make to control costs and protect the environment , but reusing lint free wipes is a false economy . In fact , it creates a network nightmare because everything becomes cross contaminated . I have personally seen a fibre tech in a telco central office ‘ cleaning ’ dozens of connectors using a disgusting , alcohol soaked rag . I am sure if the tech had an inspection scope he would have been shocked at the damage he was inflicting on his network .
Let ’ s suppose a company provides a large 9x9 inch ( 23x23cm ) wipe for their operators . That wipe becomes contaminated when a connector is wiped across it , for sure . The wipe also picks up hand oils and dust . That ’ s bad , but it gets worse .
A quality high modulus wipe is resistant to ripping , shredding and linting ; it will be unlikely to deposit debris on an end-face . But most companies buy inexpensive low modulus cellulose wipes , held together with glues . These wipes shred easily as the sharp edges of a connector rumble across the wipe . Reusing those wipes definitely will redeposit particulate onto the end-face .
Wipes are not a significant consumable expense . Let ’ s concentrate on getting the connectors really clean and avoid the expense of a repair visit . Three important tips come to mind . First , don ’ t buy large wipes ; buy the smallest possible wipes . Avoid jumbo-sized bags of wipes ; select wipes in proper packaging that will keep them clean until they are used . Lastly , teach your team that any wipe , once used , must be trashed . How much is it really saving you , if you have to waste extra time troubleshooting problems ?
Sin Seven : You can ’ t see if you don ’ t look
Every field tech and every truck should be equipped with a low power end-face inspection scope and proper end-face cleaning supplies . Even after 25 years in the industry , it still is shocking to me to see operators trying to clean fibre end-faces by wiping them on their shirts . The same lint that is removed from the dryer cage when you wash your clothes will get on the ferrule end face when you use your clothing to clean a connector . Every major equipment manufacturer and cable system maker recommends inspecting and clean when necessary before installation .
Operators do not need fancy gear to deliver a clean , quality network . A ferrule scope will cost a carrier less than two repair visits . There are convenient , award winning cleaning kits available that deliver great results for less than 10 ¢ per connector cleaned . It makes sense to spend a few pennies to save hundreds of pounds on avoidable service calls .
Avoid the costs of these sins
These Seven Deadly Sins have long been a problem within the fibre industry . Like sloth and gluttony , these fibre optic sins have added significant and avoidable costs , slowed otherwise fast networks and caused significant network down time . Simple process changes and a modicum of awareness can make a huge difference in the performance of modern networks .
We have the necessary tools and materials to avoid these sins , but just like in the Middle Ages , it ’ s all in your hands .
Previously published in ISE Magazine .
44 | March 2017