Part 1 of this series the emphasized the importance of having the proper documentation and test equipment necessary to be properly prepared for Systems Test and Integration Procedures. Without either the task is made much more difficult and not as likely to have a successful outcome. The first of Part 2 pertained only to a physical inspection of cable installed during a pre-wire phase.
Control4 Home Automation
As discussed, not all installations contain a pre-wire phase. Nevertheless, the same physical inspections and procedures for post pre-wire should be conducted prior to conducting cable terminations, although it will be significantly limited because cables installed in conduit or within walls now covered them from physical inspection. Damage to cabling can also occur accidently by other trades after it has been installed. Even if cable was installed in conduit, this does not mean that physical damage is not possible. Damage can still exist if cables were pulled without proper procedures, equipment and caution. For this and other reasons, it is important to conduct adequate and proper testing of all cabling installed to insure its integrity before termination.
Termination refers to the task of installing connectors on one or both ends of each cable or connecting one or both to their respective source and destination connections such as a terminal block. The termination task is done during what is referred to as the Termination Phase. Sometimes this is called the Trim Phase, a term used by some industries that refers to a particular phase of construction project. Regardless of the phase title, terminations for purposes of this discussion refers to the task of terminations regardless when it occurs in the installation process or what the phase title it is assigned.
Categories of Testing
There are two categories of tests that can be implemented after terminations are complete; verification and qualification. These are two distinct types of tests. Verification, just as the name implies, refers to a procedure that will verify, to a degree, the integrity of the cable and proper identification. A well developed testing plan for verification will contain a wiring list or wiring schedule that will also verify that all necessary cables have been installed or if any have been installed incorrectly. Electrical tests will determine if a cable has any damage such as a break (no continuity) or shorts between grounds or other circuits where there should not be any conductivity. It does not refer to testing the performance of the cable.
Qualification testing refers to tests that use test equipment to measure the signal quality and compares its performance to a know standard. Another term may sometime to used called certification. It represents the same test except the term certify is used when the test is to verify that the signal quality meets or excels to a standard established by a manufacture, trade organization or government regulatory. These test will confirm if the cable installed and associated connectors will perform adequately for its purpose.
Not all installations require certification, but some do and may only apply to certain aspects of an installation and not the entire system. Also, a particularly company may have a standards policy that they follow to insure quality control and a level of professionalism that the company has established for itself. If performance is not assured the system may not function as intended or with the degree of quality that may be expected by engineers, system designers or the end user.
The cost of providing these tests should be account for in the installation costs. You are not in business to provide free services. However, in a competitive arena some companies may chose not to include these costs and figure it will be worth their expenditure so make certain they have a quality reliable system. Furthermore, some companies conclude that the costs are a worthy expenditure to save on the potential costs incurred in the systems integration and final installation phases due to improper wiring or faulty equipment. This issue alone can cost a company all the profits for the job, or even worse, a loss. This is up to the business owner and the business model he has established for his company in the primary industry it servers.
Some companies choose to go straight to systems integration without any cable tests and verifications. This article addresses the technical side of these processes, but at the same time the ramifications of taking shortcuts can be expensive, so the business owner must take these issues into consideration in forming their business model and formulating a technical strategy for the company. All of it can reflect on their reputation and many sales people fail to work aggressively toward this but are no less significantly affected by such policies and procedures. Other sales personnel demands a level of quality to assure customer satisfaction and repeat business. It would be short sighted not to take this into consideration and this series of articles brings these issues into the proper perspective.
Verification Category Testing Procedures
A verification category test is be applied to all cables installed prior to the Terminations. The purpose of these procedures is to verify the integrity of the cable installed to ensure that none of the cables have been subject to damaged during their installation or by other construction trades afterwards. This is of particular concern with installations that have a pre-wire phase and cables that are not protected by conduit. Although the physical inspecting for unprotected cable required at post prewire should eliminate the chance of existing cable damaged, nothing is certain until the cable is tested.
* There is always the potential of accidental damage to cable by other trades after it is pulled at any time during construction, although this potential can be significantly reduced if proper installation techniques were followed. If the cables were installed parallel and perpendicular to the building structure, proper supports were installed and the cable ends were properly stowed afterwards, the likelihood of damage by other trades is significantly reduced.
Tests conducted at this time are low level verification. Low level terminology is essentially testing for open or short conditions and not signal quality as required for qualification or certification. These procedures also confirm that the correct cable type have been installed at the proper locations by comparing them to the prewire documents and verify their identity is labeled correctly according to the cable schedule. The timing of this task is essential because it needs to be done prior to wall finishes being applied. It is important to have the opportunity to correct the problem before the walls are finished to minimize any potential impact.
To prepare for these test procedures, it is prudent to check all cable bundling and insure that proper cable management techniques, as outlined in the DISP, have been used and remains a continued effort. This is a convenient point in the process to correct any cable management issues prior to termination. This ensures that terminations, tests and systems integration are executed in the most efficient manor possible.
The most important document used for cable test and verification procedures is the cable schedule as discussed in Part 1. The schedule should provide you with the information needed to verify that all cables have been installed with the correct cable type, the source and destination locations and that the cable identification is correct. The cable schedule should provide a check box by each cable in the list that you can use to check them off after verification of each one. If not, a simple check-mark by each line item will suffice to verify tests are completed for each and every cable.
It is also helpful to have additional information from your prepared documentation. For example, if the system is in a large building, house or other facilities with a large number of rooms, a rooms schedule can be of significant help. A room schedule is usually a drawing that shows all wall plates, control panels and other equipment installed in each room. This type of documentation not only aids in checking the cables against the wiring schedule but insures that all project documentation is correct. This is sometimes referred to as a cross-check of the documentation prior to systems integration procedures were accurate documentation is critical and is another benefit of implementing these procedures.
The type of test equipment and procedures used for these tests depend on the type of cable and sometimes its application. To accomplish low level testing the most basic test equipment will suffice. Nevertheless, it should be professional and reliable equipment. For example, tone generator testers are generally reliable and effective for determining which cable or wire is which, but it is a poor indicator of cable that may be damaged. An resistance measuring device is better than toners because they can give indication of a short that has some resistance. If you have more sophisticated test equipment, such as that required for certification testing, it can be used for these tests with some added befits. For example, a cable tester that has TDR (Time Domain Reflectometer) will not only tell you if the cable has been damaged or broken, but can also give you an indication of exactly where the cable is damaged by using its TDR capability. These will be discussed later in more detail.
Each testing procedure should take into consideration the type of cable and its usage. This will vary depending on the type of equipment and cable is installed for each project, the type of industry you serve and company policy as has been discussed. However, the basics remain the same and each testing procedure should be customized for your particular operations.
Testing for Shorted Conductors
The first test is to verify that no shorts exist in the cable between the conductors or shields. It is preferred to conduct this test first because it assumes the state of the cables are not terminated yet. This also assumes that the ends have been cut clean, properly stowed and not touching anything that may cause a short to exist. This procedure requires test instruments capable of measuring resistance in cables. This can be conducted at either end of the cable but you have to make certain that the opposite end is not connected.
Some cables when cut off at either end can form an unintentional short. If your test indicates a possible short, examine the opposite end first to confirm if this is the case. Shorts can also occur by other trades by accidentally piercing cable with nails, screws or other objects.
If you are using an ohmmeter to test cable, the resistance should be extremely low or nonexistent. Anything less than 100K ohms in most cases should be suspect. Even for long runs the resistance should be very high. However, if the cable exhibits even a high resistance on what would be an unterminated cable, it could be a result of interference. For example, if it is a long cable run that is lying in close proximity to a power line that feeds an induction motor that is currently running, it could induce enough current to give you an indication of resistance on some meters.
A quality tone generator can be used for short detection. However, using this device you run into the problem that a high resistance in the line, especially long ones, may be shorted near the other end but not sufficient to cause the tone signal to be heard and is therefore not recommended as the instrument of choice. Toners, as they are often referred, can be useful for other tests such as identity of wires in a multiple wire cable but they are not best for determining shorts in long cables and other conditions.
Testing for Open Conductors.
This procedure requires a test instrument capable of measuring resistance, such as an ohm meter. The same caution should be taken in using a tone generator for testing for shorted conductors and is not recommended. To conduct this test you need to place a short at one end of the cable while measuring the resistance at the other end. If no resistance is detected, the cable is definitely broken at some place and unable to conduct a signal.
Some caution needs to be taken with respect to testing for open conductors. Make sure that your short is a good one or you may get a false indication of a high resistance. Since all cable has resistance, some resistance will be measured while shorting the other end, especially with respect to long runs. One good way to cope with this issue is to use a resistance table found in many publications. Based on the size and type of wire, you can determine from the table what resistance you should be reading at the other end of the short based on the estimated length of the run. This will not be an issue for installations where the runs are relatively short. Knowing how long the runs are and using the tables, you should be able to determine the readings you should expect and if the resistance is too high. Also, with a second person at the other end while testing for open conductors, they can make and break the short while you watch the resistance measurement. You should see the ohmmeter drop in value whenever the short is removed.
A more reliable method for testing the continuity of cable is to use a TDR. If the cable has been damaged the TDR gives you a good estimate of where it is along the cable. If you are testing for an open cable by shorting the opposite end, the TDR should show that the short is at the end of the cable by knowing how long the cable run is that you are measuring. If the TDR tells you the distance is the same as the estimated length, then you know it is probably a correct reading and no other condition exists. You also get the benefit of the TDR capability to estimate where the problem exists along the length of the run so that you can quickly locate where the problem exists and take the best corrective action. These type of cable testers are now very inexpensive and since they can be used for testing both open and short conditions, they are well worth the investment.
In addition to a TDR, there are several low level testing instruments that can be effective for certain types of cables and applications. Multi-conductor and category cabling such as that used for telephone, data and LAN connections have specialized testers to expedite this task. For example, some testers are equipped with coded terminations that you install at one end that identifies each line. Obviously this is a tester used prominently by the telecom and computer industry. Some home installations may have several phone and data lines installed that makes this type tester valuable for most any installation company.
As emphasized in Part 1 of this series, having the right test equipment for your industry is a significant issue to be determined in establishing procedures for your particular type of installations. The primary objective of cable and test verification at this time of the installation is to determine if all the cable required to complete the installation has been installed, is installed correctly and that no significant damage has been incurred by the installers or other trades at the construction site prior making all terminations. The main purpose is to avoid costly mistakes in having to make corrective actions at a time when it will be to most expensive to do so and at a time when there is very little time left before the installation has to be complete and operational.
It is significant that cable and installation issues be resolved before systems integration takes place because they can only hinder and prolong that task at exactly the wrong time. This will be discussed when systems integration procedures are discussed in more detail.
George Wilkinson is a 35-year veteran in project management, system design, programming, testing, problem resolution, calibration and systems analysis for computer controlled audiovisual systems. He is a graduate in Electrical Engineering Technology from the University of Texas. His firm, Advanced Technological Services offers consulting, design and programming serves the commercial and home automation industry and is a certified CEDIA designer.
Â© Copyright 2006 George Wilkinson. All rights reserved.