The testing, troubleshooting, and certification phase of the project can be the difference between turning a profit and losing money on the job
The final steps in a project's finish phase are testing the system for operational efficiency, troubleshooting and fixing any problems encountered, and documenting the results of these findings. If you did a good job of designing, planning, and installing the system, this step should be relatively painless. However, if you did a poor job of planning and had to improvise and patch the system together as you went, this is the stage of the project where your profit can quickly disappear.
This article, the 11th in a 12-part series that will prepare electrical contractors to take the test to be certified as home technology integrators (HTIs), focuses on the final phase of the project: the testing and certification of the system. Testing ensures the system's connectivity and operational efficiency. If you encounter a problem at this stage of the process, you need to be prepared to quickly troubleshoot and move on with your testing. Once completely tested and documented, the installation can be certified. You can use certification to protect yourself if the homeowner contends that there are problems with the installation in the future. By certifying the cabling system, you show that your cabling job meets or beats accepted industry standards.
Low-voltage cable can easily be damaged during the rough-in and drywall installation phase of a new construction project, so it must be tested thoroughly prior to turning the system over to the homeowner. In most cases, you'll perform your tests before the dial tone is available from the telephone service provider. Therefore, the testing described here assumes that no signal or attached consumer electronics equipment is available.
When testing the installation, record the actual measured values and be sure they meet the TIA/EIA TSB-67 requirements for Level 1 or 2 accuracy. TSB-67 refers to two testing configurations, including a basic link test and channel test. It's important to note that cabling and components can't be moved during these tests. Any reconfiguration performed on the system after testing is complete requires you to retest the cable system.
Basic tests include those for open faults, shorts, crosses, and splits. An open circuit is one that isn't complete or in which the cable/fiber has been severed. A short provides a bridge across the intended load and creates a low-resistance path, or short, which bypasses the intended device, thus rendering it inoperable. A cross is a short between two terminals, typically caused by too much bare copper conductor being stripped from the end of a connection. When two wires of a pair are separated and improperly matched with wires from another pair, a split occurs. A rolled pair results when the tip and ring leads are reversed in connecting to the network. This can also create a fault on the line.
You should also check the resistance reading of the terminated cable from the audio module in the distribution panel to ensure that it's close to the measured value of the resistance of the terminals on the volume control or speaker to which it's connected. Check all audio connections for damage, and perform a continuity test, checking for loose strands and tightening all terminal screws. If the system components are available during your tests, turn the system on with the volume turned all the way down and slowly raise it to test performance to make sure it operates throughout its entire range.
Coaxial cable can be tested for continuity between the distribution panel and the termination point and for cable resistance. You can perform these tests with a multimeter or coax cable tester. Connecting a small, portable television to each video F-connector jack will give you a visible indication of cable continuity and whether or not signal level is adequate. A snowy picture is an indication that signal level is too low. One way to compensate for a low signal level is to install a video amplifier on the line. If the picture shows several wavy lines and “ghost images” in the picture, check to make sure that all terminations without equipment attached have the 75-ohm termination caps in place.
For testing unterminated RG-6 quad-shield cable, use a multimeter or volt-ohm meter to check the resistance reading between the shield and center conductor. If the meter shows a finite resistance reading below 100 K-ohms, the cable has a short in it and it fails the test. For RG-6 coax that's terminated in a splitter, or in a run with a 75-ohm termination cap, the resistance measurement should be near 75 ohms to pass the test.
Use a butt set to test all telephone cables. Stick to the following steps when testing:
Connect to the network interface device (NID) at the demarcation point.
Go off hook and listen for dial tone.
If a test number is available, call it and receive a return call; check with the phone company about test lines. Listen for clear transmission. Confirm that the digits dialed stop dial tone and that dial tone resumes when the phone hangs up. Take it off hook again.
Repeat the test for each phone line at the demarcation point.
Connect the NID to the premises wiring.
Go to each outlet in turn and repeat the test for every installed line (at each jack).
If you encounter a failure during the final verification test, check the wiring to the jack for proper connections, and check the wiring — including the distribution device — to see if any obvious disturbance has occurred since the rough-in stage of the project.
Your test instruments must meet or exceed the applicable requirements in TSB-67. Commercially available instruments will specify whether they meet Level 1 or Level 2 accuracy. To meet TSB-67 standards, a Cat. 5 tester must be able to test for length for all pairs of an installed link, attenuation, and near-end crosstalk (NEXT). Testers may also measure for delay on an installed link, which is the time it takes for a signal to travel from one point to another. The simplest way to perform basic testing is to use a multimeter or volt-ohm meter and test for both shorts and continuity.
You should also conduct a continuity/wire map test, or channel test, to verify end-to-end connectivity. Perform tests on the length of cable from the distribution panel to a junction box; no cable length should exceed 295 ft.
Most manufacturers usually offer test equipment and troubleshooting tips with every device they offer. It's advisable to familiarize yourself with these recommendations prior to the start of any testing.
The ability to effectively troubleshoot computer-related problems is an important skill when working with home networking equipment and systems. The processes used typically require you to follow a systematic approach to troubleshooting. Some of the following suggestions are more advanced than what you find on most projects, but they're worth noting for those times when standard troubleshooting techniques just don't seem to be working:
Begin troubleshooting by gathering information about the symptoms and operating characteristics of the software and hardware problems found on the system. Make sure to note any recent changes that have occurred on the system.
You should then focus on locating the problem. There are three major steps to finding the location of an error:
Examine and test connectors at both wiring closet and remote jack ends of the cable.
Visually inspect cable runs where they make sharp bends, pass through constricted areas, or are in close proximity to sharp metal edges and surfaces. Look for bends, cracks, or breaks.
Test the cable run with a time-domain reflectometer (TDR) to determine how far the problem is located from the end of the cable tested.
After gathering information and locating the problem(s), move on to identifying potential solutions. Check the simplest possible causes first, like whether the power is on. Focus on hardware before software. Start with the physical layer of the OSI model, then move to the data link and network layer. Troubleshoot from the bottom up. Always check the OSI Layer 1 first.
RJ-11 and RJ-45 modular plugs are often manufactured in such a way that you can look at the plug to see if conductors are in contact with the plug's contact pins. Transparent plugs also make it easy to see whether you or another installer has adhered to specifications regarding untwisted wires. Although problems with coax and serial cables aren't as easy to identify with visual inspection, in many cases you can disassemble their plug shell to verify connection of the conductor to connector pins.
Now you're ready to correct the problem(s) you've identified. By far, connectors and cable endpoints are the most common locations in which errors occur. In order to correct connector problems, you must understand the nature of a correct connection and be aware of the requirements put in place by the various standards organizations for connectors that meet certification levels.
The work required to correct a bad termination can range from re-terminating the cable to splicing in a new section of cable or pulling in an entirely new cable. Splicing shouldn't be considered an option for most residential networking and entertainment cables.
In reality, repairing connections is the most common repair to be made. In most cable types used for residential networking systems, cable replacement is a far more reliable and ultimately cost effective solution than trying to splice a section of new cable into the run.
After you think you've found the problem and corrected it, double-check to make sure everything still works. If not, you'll need to go back to Step 2 and try to pinpoint the problem. If the repair does fix the problem, then move on to the last step.
Any time you make a repair to the system, you must document the corrections. This documentation will aid in the tracking down of future problems, and be invaluable to you when it's time to make changes to the physical plant. Change notes should include the following information:
Date of the change
Reason for change, including symptoms, diagnostic tools used, and final diagnosis of the problem
Person making the change. Each technician should take responsibility for his or her own work.
This may seem like a lot of trouble for each change made, especially if the change involves simply re-terminating a cable. When a copy of the change record is presented to the customer with the final documentation bundle, however, it will provide persuasive evidence of a thorough testing effort for the infrastructure of the system. In addition, some manufacturers require documentation to honor the warranty on their equipment.
Dusthimer is publisher of Cisco Learning Institute Press, York, Pa.
Sidebar: How a TDR Operates
A TDR operates by injecting a signal into one end of a cable and then measuring the delay until the reflected signal returns to the device. The time measured is used to calculate the length of the cable. If the returned length is different from the total length of the cable run, there is a break in the conductor at the point indicated by the TDR. It's a simple concept, but one that requires high-speed electronics to execute.
To properly operate this piece of test equipment you must be trained to evaluate whether spikes mean shorts or open circuits, what may be assumed from the presence of multiple echoes, and the importance of dips in the display. Newer TDR units remove much of the interpretation from the user's responsibility, providing readouts on error type, circuit length, and other information discovered through testing.