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ISE Columnist Don McCarty, OSP Expert

Provisioning And Maintaining POTS Circuits

Feb. 1, 2022
I feel privileged to have participated in the growth of the telecommunications industry. I’ve trained copper cable technicians for 50 years and, […]

An Old Telco Guy Looks Back, Moves Forward

I feel privileged to have participated in the growth of the telecommunications industry. I’ve trained copper cable technicians for 50 years and, although at age 78 I’m no longer up for the constant travel, I continue to write and consult. Every month I post my cell number so techs can call or text for advice — and I love hearing from you. 

Looking both backwards and forwards, it’s mind boggling to think that over the past 150 years, we’ve gone from the genesis of the telecommunications industry — telegraph machines, and wire and Morse code — to the massively distributed fiber that enables an ultra-fast and highly reliable broadband industry. 

Yet between telegraph wire and fiber is the long, long history of the hard-working, paired-copper industry. 

Copper cable experienced tremendous change in physical composition before it was able to step up as the precursor to expanded telecommunications opportunities. Starting as paper- or pulp-insulated copper encased in lead, water ingress was a constant problem, and customers experienced massive telephone line failures with every big storm. 

Eventually, cable providers created filled PIC, making copper a stable platform that could support the birth of a true telecommunications industry that began with FAX machines and modems. And, so came the advent of the Internet — and we were off to the races! From there, the passion for more, faster, and better, brought us to tremendous advancements in copper and eventually to fiber.

I welcome fiber and all the good it has brought. It’s enabled global connection and helped drive down the prices of technology as the number of users of digital equipment, whether personal use or business use, has expanded dramatically. Every day new services, applications, and products, dependent upon broadband service are created, driving the demand for faster connectivity. Even though I date back many, many years, I struggle to remember a world without the many benefits of digital technology enabled by fast Internet that we enjoy today. 

With the capabilities and efficiency of fiber, is there a fit for copper in the future? While it won’t be soon enough, I believe that one day we will have fiber to nearly every residence. Nevertheless, the role of copper continues to grow because of demand in the data center, where copper cable is shown to provide fast transmission up to 10 meters. And used inside away from elements, rodents, and electrical noise, it remains cost-effective, highly reliable, low latency, and draws little power. 

New technology like Power over Ethernet (PoE) continues to push the technical capabilities of copper. 

What I worry about is the many customers who still depend upon copper for phone, TV, and Internet. It’s not profitable to extend fiber to many. Telcos are abandoning these previously loyal customers. For those telcos who still support customers dependent on paired copper, they have fewer and fewer techs who have the training needed to deal with the challenges of locating faults, repairing, and maintaining, copper cable; it’s a lot more complex than repairs to fiber. 

For those technicians who do the hard work to become copper experts, you are heroines and heroes, and I thank you for your dedication and talent. I’m here for you, and hope my words help. And please call if you are stuck. I mean that.

There is much more to the story of how copper fits in the business environment, but I’m out of my league here and others can tell this story much better.

An interesting tidbit: if you are familiar with POTS, you may be incorrect about what that term meant initially. POTS is not Plain Old Telephone Service but is Post Office Telephone Service. Switching operators were federal employees located in the local post office buildings.  

So now it’s time for my regular lecture on provisioning cable.

From time to time we receive a call from a field technician who is having p problem restoring service to a POTS circuit. They test the cable pair with their multi-function test set looking for DC faults. When found and fixed, in most instances, service is restored. Those cases of trouble that are still not working can often be attributed to a transmission or a circuit design fault. These types of faults really eat up field technician’s time and are the root cause of many repeat reports. Fortunately, today’s field technician’s multi-function test set has transmission testing capability built into it. 

Circuit Design Fault

As an example of a circuit design fault, I was in the field with a technician who was the third man out working on a repeat complaint from a fire station reporting no dial tone at times. The line tested good. We were only a couple of miles from the Central Office (CO), so low current should not have been a factor. 

I suggested running transmission tests, as everything else checked out but nothing was fixed. The set showed a low loop current condition measuring around 20 mA. Other pairs in the same count also tested low. Loop treatment was indicated because of a circuit design problem. 

A week later, the technician called with the fix. A new CO had been installed and fed the fire station with only 26 gauge cable. The fire station and all subscribers beyond the fire station needed loop treatment.

So, check that loop current. Insufficient loop current might be the culprit in such complaints as: no dial tone, reach wrong numbers, can’t be heard, bell rings, can’t answer bell rings after answer. Loop current must be sufficient to provide talk battery and operate supervision and signaling equipment, such as: dial tone request, touch-tone pad operation, ring trip when a call is answered, and talk battery to the telephone transmitted. 

When used at the network interface, a transmission test set simulates any telephone in the house when measuring loop current. If the current is inadequate at the network interface, the telco’s responsibility for loop current is met. So, when it is low, loop treatment is in order.

Excessive Loss

Loss is next. Loss and current problems are usually interrelated. If a current problem exists, most likely so does excessive loss. Such a problem affects both touch-tone performance and voice volume.

The Telcos guarantee a minimum acceptable standard of sound over their lines. A transmission test set determines that the standard is met much better than the human ear can. Loss tests measure the sound characteristics of a circuit in decibels (dB). The amplitude of the signal is attenuated by 4 primary factors: conductor resistance, insulation loss, capacitance, and inductance. 

When a marginal or unacceptable loss is encountered, it is affected by the entire circuit, including bridged tap and wire beyond the customer. 

  • If such a condition is suspected, test the neighbor’s pair. 
  • If loss is acceptable there, test both pairs for loop treatment. 
  • If the acceptable pair is treated, order treatment for the trouble pair. 
  • If the neighbor’s pair is not treated, you have a single pair problem here (excessive bridged tap or wire beyond the workout terminal. 

Only when loss is found acceptable can the next parameter be tested.

Just listening for noise on a circuit can be an almost futile task. Let’s take the intermittent noise complaint: the customer complains in the evening of high noise. A technician is dispatched in the morning and checks the circuit at 10:00 A.M. — when everyone is at work and the power influence in the area is down. The circuit sounds good. The customer comes home, and, like everyone else in the neighborhood, turns on the TV, the stove, and the washer and dryer. The power load increases, power influence goes up, and the line noises up.

This noise heard by the customer is often caused by such physical factors as pair trouble, an open lateral, water, or bad splicing. If all physical factors test OK, the noise is most probably caused by induced AC current from adjacent power lines. This is often called line born noise and is caused by an imbalance in the capacitance or resistance of the pair. 

If the pair is balanced, the AC current flow is equal and opposite, thus canceling, and no current flows to ground. Any unbalance, either resistive or capacitive, causes current (equal to the difference in the balance between the 2 conductors) to flow to ground and "noiseup" the circuit.

Balance Is Critical

Circuit noise (noise metallic) and power influence are interrelated, each being dependent upon the other to form acceptable balance.

When noise metallic is marginal or unacceptable and power influence is acceptable, suspect a pair problem and go after it. The pair is unbalanced either resistively (going open) or capacitively (one side open on a lateral, beyond the workout terminal, or crossed with a nonworking pair). 

In most instances, a capacitive unbalance can be identified and isolated with an open meter. If not, use the location techniques for finding a resistive unbalance. This type of problem pertains only to this pair and this customer, and can be isolated and repaired by the first man out.

When both noise metallic and power influence are marginal or unacceptable, suspect a grounding, bonding, or associated power company problem (open capacitor bank, bad transformer, open neutral, etc.). These are problems for a transmission team. But record the test results.

The records of all field tests allow computer analysis of the approximate area of the problem, and the trouble can quickly be pinned down by the transmission team. They wouldn’t have the slightest clue as to where to start without the technician’s original input.

A Final Thought

While at the network interface, check the network interface ground. Use the transmission test set to measure the resistance between the CO ground and the protector ground. The station ground should test 25 Ohms or less to assure that the carbons at the protector fires when power or lightning is present on the circuit, and protects the customer and station equipment from damage. If the test shows resistance greater than 25 Ohms, remake the ground.

Circuit quality is an individual responsibility. No one but the field technician, standing at the protector with dial tone present, can guarantee that the service is acceptable. If this is understood in all levels of outside plant responsibilities, the customer will be taken care of both immediately and, equally important, in the long term.

Signing Off
First, I wish us all a wonderful 2022. We all hope the challenges of the past 2 years are fading. If you are a copper tech, please maintain your best copper skills because many people depend upon you and will for some time to come. I hope this column is of interest. If so, let me know. And, if not, also let me know. I’m always looking for ideas for my next column and your input is valued. You can reach me at [email protected] or text or call me at 831.818.3930. Thank you for your readership.

About the Author

Don McCarty

Don McCarty is the OSP EXPERT columnist for ISE magazine, discussing the issues around provisioning, testing, and maintaining copper for all services from POTs to IPTV. Don is also president of and the lead trainer for McCarty Products, a technical training and products company training field technicians, cable maintenance, installation repair, and Central Office technicians and managers. For more information, email [email protected] or visit