In an earlier column we discussed the proactive process of finding single pair faults in the copper infrastructure rather than moving the customer to another cable pair to restore service. This proactive approach of finding and fixing single pair faults will resolve problems in 95% or more of your copper infrastructure customers, and quickly gets them back in service. Additionally, adhering to this process can support identifying other potential pedestal and terminal problems that can be repaired before customer service is affected.
The other 5% of service interruptions occur in bad sections of cable, both aerial and buried, in the copper infrastructure plant. Think about it: only 5% of cable faults in your copper infrastructure takes up over 80% of your field technician’s day. The scary part is the fact that your field technicians typically know where every bad section is and have most likely told your management team and engineers about them but there wasn’t time to deal with the problem.
If you decide to remain reactive with your copper infrastructure until you have completed a fiber overbuild, don’t be surprised to find your customer has moved on to your competition.
The root causes of section failure in the copper infrastructure are: water in air-core PIC cables around 15%; water in splices and encapsulations around 50%; sheath or shield damage around 30%; and phase power and lightning faults around 5%.
Most root causes of these faults could be found and fixed or replaced within a week of the first trouble report but are reactively drug out over a period of months, and sometime years, using a cut-to-clear transferring the customer to another cable pair until there are no more good pairs left.
If you decide to go proactive, pick a faulted section and go for it. You will be able to find and fix at least 50% of them within a few months. To give you an example, at one Telco in South Carolina we fixed 15 bad sections that had wet buried splices or sheath damage and replaced 3 sections with water in the section in 2 weeks. Countless customer complaints were solved.
To do proper section analysis, your field tech has a multi-function test set with a Digital Multi-Meter (DMM), a Resistive Fault Locator (RFL) feature, an open meter feature, and a Time Domain Reflectometer (TDR). These are used to identify the types of faults, resistive and capacitance, and to measure the distance to the faults. For buried plant a cable locator will show the cable path, and a shield or conductor to earth frame will pinpoint the fault.
Make sure that you know how much cable there is in the section even if you need to locate every foot between pedestals and measure the footage with an engineering wheel.
Testing faulted cable pairs with your DMM will indicate the type of section failure that you are dealing with. I refer to this as a pattern of symptoms. Following are some examples of actual section failures that I and Telco field techs worked on.
The first example was a 700-foot section of a 100-pair single sheath air-core PIC cable. Testing several vacant cable pairs showed crossed battery and high resistance grounds on ring conductors only. Most tip conductors tested clear. This is an indication of water in a section.
To confirm this finding, the bond was removed on both ends of the section and the isolated shield was tested to ground. -15 volts DC on the shield confirmed our suspicions. When measuring a vacant open pair, the test set open meter showed 1,100 feet of cable in the section. Water shorts the capacitance of the cable pair causing the open meter to read long.
When using the RFL feature, faults measured random distances from around 200 feet to 500 feet in the section. The TDR showed water starting at 200 feet from one end and 500 feet from the other end. This is a business case for a section replacement. From this point on it is up to engineering and the management team. No more measurements are needed.
The second example was a 300-foot section of a filled 25-pair cable. Testing cable pairs with the DMM showed high resistance grounded and shorted cable pairs with crossed battery on both tip and ring to ground. These patterns of symptoms indicate that the root cause of the section failure is a wet splice or encapsulation.
Had the DMM shown solid shorts and solid ring and tip grounds, we would have suspected shield damage which could be pinpointed with the earth frame in a matter of minutes. RFL measurements showed the wet splice at 100 feet from the test point, the TDR showed the splice at 100 feet and the earth frame confirmed it.
Business plans to repair or replace faulted sections will heal your wounded copper infrastructure, and will allow you to provide quality bandwidth and other services on your existing copper network until the copper network is replaced.
If your company has a well-established proactive plan, let me know about it; I like to write positive columns about good work that’s happening. If you have a case of trouble that you are struggling with, call me and we can brainstorm solutions. If we can write about it (anonymously is fine), then others can learn from your situation. Contact me at firstname.lastname@example.org or call 831.818.3930.