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As you may know, the Telecommunications Industry Association (TIA) has agreed that Level III-qualified testers are to be used when certifying or verifying Category 6 cabling systems (Category 6 cable is a 100-Ohm cable with transmission characteristics specified up to 250 MHz).
Here are some guidelines to handle the contractor’s testing responsibilities. Note: If you are planning to include testing of Category 6 installations, be sure the tester you use is capable of handling 250 MHz (required for a Level III tester).
Basic or Verification Testing: This testing confirms continuity and the absence of faults that could have been created during installation.
A wire map test can identify installation wiring errors, check for end-to-end pin-to-pin connectivity, split pairs and detects if there are any crossovers, shorts, split pairs, reversed pairs, opens or breaks or any other miswires. Physical length may be tested as well. Physical length is not electrical length and can be slightly less, due to the twisting of the conductors.
Manufacturer Testing: This is testing that shows the cabling performance meets or exceeds the appropriate category of cabling (Category 6 as in TIA-568-B.2 and in B.2, Addendum 1). Tests are done for the manufacturer by a third party in their test lab and under conditions that meet industry standards. The mark on the cable jacket is evidence that the manufacturer had a national research test lab (NRTL) test that cabling product to TIA and other standards, and that it passed.
Verification testing may be performed on samples and done periodically.
Certification Testing Performed On-Site: This confirms that the installed cabling’s performance meets or exceeds Category 6 cabling standards (as in TIA-568-B.2 and in B.2, Addendum 1). This “flavor” of testing also verifies that the installation practices used in the field were done “to standard,” such as no untwisting of conductors for a distance of more than one-half inch up to termination.
With a Category 6 cable installation, it is very important that installation practices be followed, because there may be some non-standard-compliant components or hardware products used.
Here is a list of tests required by the TIA standard (TIA-568-B.2, Addendum 1 for Category 6 cabling and for Category 6 connecting hardware):
o Insertion Loss (IL)—IL is a measure of signal loss.
o NEXT Loss (pair to pair)—NEXT is an unwanted signal (crosstalk). n FEXT loss and ELFEXT (pair to pair)—Far-end Crosstalk (FEXT) is crosstalk measured at the opposite end from which the disturbing signal is transmitted.
o Return Loss (RL)—RL is the measure of the reflected energy caused by impedance mismatches in the cabling system. Greater return loss means better performance.
o Propagation Delay (PD)—PD is the amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a cable or the cabling. n Delay Skew (DS)—DS is the difference in propagation delay between the fastest and slowest pair in a cable or cabling system.
o Longitudinal Conversion Loss (LCL)—Balance at the near end.
o Longitudinal Conversion Transmission Loss (LCTL)—Balance for transmitted signals.
Level III tester testing The cabling is tested prior to the installation of the LAN equipment. These testers have minimum requirements specified for them to qualify as a Level III. Specs involve attenuation/insertion loss, NEXT and PSNEXT loss, ELFEXT/PSELFEXT, and return loss, and range from baseline specs to the channel and permanent link configurations—some include propagation delay and delay skew. A plus for a handheld tester is that it may also be certified/verified by an unbiased third-party organization.
Active network testing After the installation is done and the network is under demand, further testing may come up and is beyond the scope of this article. There is a lot of responsibility on the contractor (which is sometimes accepted and sometimes not) to provide correct and clear verification and certification information after a job is complete. Along with performing the tests, there is also a high degree of professionalism associated with the presentation of test data. A compilation of the specs, met in a well-arranged binder or in a software database format, can go a long way toward promoting you as an expert in your field. EC
SALIMANDO is a Vienna, Va.-based freelance writer and frequent contributor to ELECTRICAL CONTRACTOR. He can be reached at [email protected].
You can find more information on physical layer standards in the Cabling Standards UPDATE, written and published by Business Communication Services (BCS) with Joe Salimando. The UPDATE is the only independent report in this industry; published since 1995, it has consistently covered active United States standards groups and appropriate international standards work. Visit the Web site at www.cablingstandards.com for more information, or call BCS at (209) 295-3975.