Telephone Systems [Troubleshooting and Repairing Commercial Electrical Equipment]

For centuries, a nonelectrical acoustic device, like children make from two tin cans and a string, was known and worked surprisingly well for medium-distance voice communication. It bears the suggestive name "lovers' telephone" and was the ancestor of the acoustic devices we are so fond of today. From that pleasant diversion and the astonishing success of coast-to-coast and later transcontinental telegraphy in the nineteenth century, came the impetus for a worldwide high-quality telephone network, with perhaps five billion connected outlets including cell phones. A few decades ago, you had to shout to make yourself heard in a coast-to-coast call. Now, two or more people can speak via conference call to China and the sound quality is the same as being next door.

Alongside all this technical progress, the in-premises part of the infrastructure has become accessible through a process known as deregulation. The original business model had the utility owning all the equipment including the in-house wiring harness and the phone itself. Utility workers did the original installation plus any subsequent repair work, regardless of whether it was a modest cottage with one jack or a large office building with many individual lines and extensions and an in-house switchboard.

To bend and shape large (1/0 and up) insulated conductors in order to make meter socket and panel terminations, use the hole, with its well-rounded edges, at the end of a large adjustable wrench handle.

Generally, the network installation and wiring were satisfactory, but the work from the point of view of appearance left much to be desired. If phone extensions were to be installed in many rooms in a house, the cabling was spider-webbed from a box on the street side of the house by means of tacking the lines to the siding outdoors and drilling in to the location of each phone. For splices, wires were twisted together, taped, and left to withstand the elements. The securing hardware was spaced far enough apart to ensure that the wires would flap in the wind and sag between supports. When repairs were made, abandoned lines were left in place for the life of the building.

Now, all premises telephone wiring has become privatized. In a commercial building, in-house electricians or maintenance personnel do the cabling, or the work is hired out to a cabling contractor or outside electricians who include such tasks in their job description.

Overall, a much higher degree of professionalism prevails. If an extension is to be added in an office, the cable will be fished behind paneling or whatever it takes to conceal it. For factory work, a new run of EMT will be added, rather than hanging the cable from an existing unrelated raceway, which is a National Electrical Code (NEC) violation.

In troubleshooting and repairing premises telephone systems, it is important to maintain a high standard of workmanship, and to strive to create a product that, in addition to being reliable for years to come and convenient to use, will have a good, simple appearance without any unnecessary wiring or hardware that would be perceived as clutter.

If your troubleshooting and repair will involve any alteration or addition to the existing installation, it is vital to refer to the current NEC edition and to adhere to any applicable mandates. Previously, we outlined NEC requirements for data and communication wiring, specifically removal of abandoned cable and the cable hierarchy, which permits substitution of plenum cable in riser applications, but does not permit substitution of riser cable in plenum applications, to give a typical example.

PBX and Multiplexing In a medium-sized commercial setting such as an office building with 500 lines, there may be a private branch exchange (PBX) on the premises, and it is interesting to see how it works. If the commercial site is a complex of buildings, it is likely that the electrical equipment that makes up the PBX will be housed in a small concrete building with no windows (to deter vandals). This is known as a central office. Into this building via a large diameter cable with typically 75 pairs of telephone wires come voice and data communication with the outside world. How is it possible that this trunk line is able to serve a system with as many as 500 lines? The answer is through the miracle of multiplexing.

This is an umbrella term for various methods for combining several analog or digital signals into one signal that can be transmitted in real time over a single line. Without going into the details because this knowledge is not relevant to troubleshooting phone lines within the PBX or in premises telephony, here is a list of multiplex methods:

• Space division

• Frequency division

• Time division

• Polarization division

• Orbital angular momentum

• Code division

The PBX contains equipment to de-multiplex these incoming calls and prepare them for distribution throughout the branch lines or the reverse. The heart of the PBX, and the entire phone system, is the switch, which takes the place of the old human-operated switchboard that predated the dial telephone system. A central office from years ago was a noisy affair, with many operators simultaneously speaking to customers or, later, mechanical relays clacking in response to dialed calls from all parts of the exchange or in response to incoming calls from anywhere in the world.

A modern central office is eerily silent except when an alarm sounds. The switch is entirely silent. It is electronic, and within its protected environment are one or more rows of floor-to-ceiling enclosures. It is quite reliable. For each branch line, there is a dedicated slot within an enclosure containing a printed circuit card. These occasionally become defective, and can easily be swapped out, using the normal procedures to avoid static electricity-caused damage in handling. From there, the individual lines emerge to a cross-connect, where local lines are connected. They merge into one or more large, multipair cables that go to a centrally located cross-connect panel typically on separate floors in a building or in separate buildings.

The switch is computer-controlled from within the central office, in the premises maintenance office, or off-site via an Internet connection. Computer access to the switch is password protected, and there is the capability to control from anywhere in the world the many parameters of the system as a whole in addition to the properties of each user line.

Telephone numbers, methods for accessing an outside line, call waiting, and caller ID are a few of the attributes that are accessed and controlled in this way. The details and full range of capabilities vary among different manufacturers, but what they have in common is multivolume print and online documentation with extensive error-code and troubleshooting information. Tech help is also available.

Large electrolytic capacitors have a limited shelf life. In the case of a good one, an ohmmeter set on a high range will "count" first one way and then the other as the leads are reversed and the internal meter battery alternately charges and discharges the capacitor. Sometimes a bad electrolytic capacitor can be brought back to life by applying a steady dc voltage for a long time.

A large commercial or industrial complex with an on-site PBX will need at least one individual, maintenance electrician, or telecom specialist who has obtained the knowledge and expertise necessary to operate the computer-controlled switch in order to troubleshoot and repair lines as needed.

Reliability is a high-priority design goal for the switch and associated equipment. To this end, the central office building must be carefully designed and built. Extensive grounding with a rugged, low impedance, conduit enclosed grounding electrode conductor is essential.

Ufer technology, which means concrete-encased metal in contact with the ground, makes for an excellent grounding electrode, far better than the usual ground rods used in many types of construction. However, this method will not be effective if there is plastic or foam under the concrete, or if the rebar is covered by paint, epoxy, or other insulating coating. Other possibilities are a copper ground ring, plate, or mat under the building, or any of these in combination, possibly with additional ground rods. Regardless of the grounding method, a low-impedance connection to earth is desirable for a variety of reasons, particularly lightning protection, voltage stabilization, and protection from ac hum in the phone system.

An ordinary electrical service will be brought to the central office, but it is important that the telephone system functions without interruption during a power outage, regardless of duration. This is possible because of a large battery bank inside the central office. It is always online and receiving a maintenance charge from equipment that is connected to the utility supply. A highly visible digital voltage readout is connected to each cell. Proactive cell replacement, cable, and connections inspection and servicing should be part of the maintenance procedure. Additionally, there must be a backup generator, located immediately outside of the building and situated so that exhaust fumes will not get into the building's air intake. The generator is usually LPG or diesel. It starts automatically in the event of an outage, and takes over battery charging and building services. The automatic transfer switch ensures that there will not be backfed energy into the utility lines, which would endanger line workers. Periodically, the backup generator starts automatically and runs for a few minutes. Maintenance should include changing oil, inspecting belts, and checking the condition of the starting battery, including battery cable connections, as well as coolant level and condition. For these procedures, refer to the owner's manual.

When soldering electrical work, use resin, not acid flux, which is good for water pipes and radiators, but will leave a corrosive residue on printed circuits boards and the like that will eventually compromise the conductivity of an otherwise properly soldered joint.

The central office requires other features in order to provide reliable phone service throughout the exchange. There has to be very reliable air-conditioning. This goes way beyond worker comfort. It is necessary to prevent temperature rise due to the large amount of heat that is generated by the switch electronics, lighting, battery charging, etc. It has to be sized out in conjunction with the highest anticipated outdoor ambient temperature. In addition, there must be reliable heat adequate for a prolonged winter cold spell. The temperature inside can be measured and automatically reported to the facility maintenance department, using inexpensive hardware. Keep in mind that excessive heat, due to failure of the air-conditioning, could fry over $1 million worth of electronics and make for a prolonged and widespread communications outage. Lighting must be adequate for exacting repair tasks that could become necessary. Needless to say, the roofing and structural integrity of the building must be sufficient to ensure that the large capital investment is not at risk.

We have outlined a relatively simple telephone system with PBX. If you have assimilated the switch documentation, including learning command-line entries for setting switch and individual line parameters, you know how to make keyboard queries, and you know the cabling layout, then you will be equipped to troubleshoot and maintain the telephone system and to perform alterations and additions to it as needed for day-to-day operations.

Phone Diagnosis and Repair

Troubleshooting a phone system is a little different from other types of electrical work. In some ways it is easier, although without the right tools and orderly work methods, some tasks can become overwhelming. There is much specialized equipment for telephone diagnosis and repair, but only a few simple tools are needed to get started. Besides ordinary electricians' tools such as a good multimeter, fish tape, hole saws, long electricians' drill bits, a complete set of hand tools and cordless drill/screwdriver, the following specialized telephone tools will be required:

• A telephone test set (butt set) is essential for almost every repair job. This is a compact phone with built-in line-powered electronics and keypad dialing. Leads with alligator clips are included. Simple models are available for under $100, but prices escalate if you want advanced features.

• A toner is an audio-frequency generator powered by a 9-volt dry cell. It has two leads with alligator clips or a short line cord with modular plug. You can inject the tone into a telephone line at any available point and listen for it elsewhere with a good connected phone or butt set. It is the preferred method for tracing and identifying lines with no helper required. You can attach it at the jack and work back toward the central office, indoors or outside. On the other hand, you can attach it at the central office and work downstream.

• A wand is a simple, noncontact (proximity) probe that allows you to find the pair carrying the tone merely by bringing the tool within a couple of inches of it. You can pass over large bundles of pairs quickly and know by the intensity of the tone when the extension has been found, so this device is a great time-saver.

• Some jacks and blocks have specialized terminations. The wires are not stripped, but "punched down" with a spring-loaded tool, and the terminations at the device pierce the insulation. The result is a good electrical connection that is sufficiently strong for the purpose. You can make these connections with needle-nose pliers, but the results are not consistent. You really need a punch-down tool. The only problem is that there is more than one style of termination, and each takes a different punch-down tool or different blades. The different connector types are 66, 110, BIX, and Krone.

• A wire-wrap/unwrap tool may be needed to work on the cross-connect frame within a central office. This is used for many types of electronic work. A detailed instruction manual comes with the tool, and it makes a very neat, durable connection with excellent electrical properties.

These are the principal tools needed for telephone branch line work, so it is inexpensive to get into the trade on this level.

Dead Phone Syndrome

Frequently, the electrician or telecom technician is called to check out a phone that is dead or noisy. Obviously, you need to find out whether the phone or the line is at fault. Pick up the receiver and see if there is a dial tone. If not, wiggle the modular connections at both ends of the receiver cord and line cord. If there is a response, most likely the fault is in the cord, which should be discarded and replaced. If there is no response, you will need to go deeper, but it is premature to rule out these cords. The best quick check is to plug a known good phone into the modular jack. If there is now a dial tone, and the good phone is appropriate for the location, you can leave it at that and the repair is complete. Take the bad phone back to your shop for further tests. Alternatively, you can try swapping out receiver and line cords, or just the receiver.

If there is still no dial tone, pull the cover off the jack and check terminations and the incoming line with your butt set. If it is a two-line setup, try the other line. Often, in seeking to make a dial-up Internet connection, someone will plug the phone into the wrong line connector, which may have been discontinued with the advent of wireless, and this is the reason for the "dead phone." A shorted line or equipment (including computer, fax, or credit card terminal) may be plugged into a jack in the same room or nearby, or one of the lines or jacks may become shorted. A short circuit anywhere on a daisy-chained line will make for a dead line and phone. If this sort of problem is suspected, the best course of action is to disconnect all the phones and other equipment that are on the line and see if that brings back the dial tone. If it does, you can plug them in one at a time to find which one is at fault. If this does not bring back the dial tone, go to the first (farthest upstream) jack on the line, and check for the dial tone. If there is none, disconnect the downstream devices starting at the first jack to see if the problem is a downstream short that is pulling down the connection. With the feed from the central office disconnected and all devices unplugged, ordinary ohm readings with a multimeter are useful. You can shunt out the last jack and take it from there, taking care that the line is disconnected at the first jack.

Short pieces of the jacket of Cat 5e cable with conductors removed make good protective sheathes for small conductors such as motor leads that may chafe. These pieces can also be used as sleeves to identify multiple ends that are to be terminated later. A fine-point felt-tip pen works for labeling the individual tubes.

All of this assumes that you know the order in which the jacks are fed, and from which end. This may not be evident if the cabling is concealed behind wall or ceiling finish. In any event, there are some procedures to follow before fishing any new lines. You can put your toner on the jack and work back toward the central office, checking upstream for dial tone and downstream for tone. This should reveal the location of the faulted line segment, if that is the case. Ohmmeter readings will let you know if it is a short or open. If you find a bad line, and if the line was run in Cat 5e so that there are unused spare pairs, you may find a good pair and swing over to it at both ends. This could be the case if an errant nail damaged one pair in the line. Otherwise, it could be necessary to run a new line.

An alternative method is to start at the central office. Equipment from different manufacturers includes various diagnostic capabilities including the ability to test the line.

An on-screen report is generated that includes the resistance of the line read from the switch.

Depending on the result, it may be possible to locate and repair the fault, swing over to a good unused pair, or run a new line.

If there is no dial tone at the central office where the pair comes out of the switch (with the downstream line disconnected), you probably have a dead card. It can easily be swapped out and reprogrammed if you have a good card on hand, but beware of static electricity in handling a card. There should be a grounding bracelet available at the switch enclosure. If not, consider installing one. In addition, it is important not to have bad cards floating around and mixing with the inventory of good spare cards, so keep track, label, and document everything. Cards are very expensive.

Why Use Cat 5e? Any new lines should be run in Cat 5e. This makes a high-quality inexpensive phone line that is easy to work with, and it provides excellent color-coding with the potential to upgrade single-line phones to two lines and to replace damaged pairs without running new lines.

When bringing Cat 5e into a jack, strip back the outer jacket so that it ends approximately ½ in. inside the enclosure. Leave all pairs the full length, and wrap unused pairs around the part of the jacket that is inside the jack. This makes a good strain relief, keeps the extra pairs compact so that the jack is not overcrowded, and makes them available for future use.

Noisy lines are similar to dead lines, as far as troubleshooting techniques are concerned.

Noise is caused by an intermittent short or open anywhere along the line, in the phone, or very often in the receiver, receiver cord, or line cord. These faults can often be located by wiggling the connections at both ends of the cords and at the jack, or by phone substitution.

Underground extensions, such as when there is a phone in an outbuilding, are a frequent source of noise, often due to water in the conduit (usually PVC), frost movement at either end, or moisture in an unheated building. This can be checked by temporarily disconnecting the underground line at its source. It is necessary to disconnect both wires because noise will result if either one of them is subject to intermittent grounding. If there is an ac hum, it may be from the central office or, more likely, the phone line is run close to a power line, fluorescent ballast, motor, or some other nonlinear load.