In the past, ANSI/TIA standards indicated that 28 AWG patch cord cables didn’t meet requirements – and, as a result, shouldn’t be used. Instead, the standard specifically stated that all cables in structured cabling should consist of four balanced twisted-pairs of 22 AWG to 26 AWG cable.
As technology improves, however, and as the industry becomes more comfortable and familiar with 28 AWG cable, we’re starting to see it used in data center and enterprise network applications for many reasons:
As a result, earlier this year, TIA decided to establish a normative annex to ANSI/TIA-568.2-D that contains performance information about 28 AWG patch cords.
Generally, this standard requires conductor sizes of 22 AWG to 24 AWG in horizontal cables, and 24 AWG to 26 AWG in patch cord cables. But, TIA has recognized that, in certain cases, it may be necessary or desirable to use 28 AWG cable cords. Using 28 AWG will now be allowed as part of the standard – as long as ANSI/TIA-568.2-D requirements are followed.
A few of these important ANSI/TIA-568.2-D requirements are discussed in detail below...
DC resistance – a measure of how difficult it is to pass a DC current through a conductor – shall be measured in accordance with ASTM D4566, which outlines standard test methods for electrical performance properties of cable insulation and jackets.
For all cable categories, the DC loop resistance of any structured cabling channel shall not exceed 25 Ω corrected to a temperature of 20 degrees C.
To make sure that your structured cabling channel will meet the DC loop resistance, it is recommended to keep the overall length of 28 AWG patch cords to a minimum (less than 15 m). Longer lengths are possible, but special attention to the overall DC loop resistance would be required.
It’s safe to assume that, in most cases, cable with a large OD has less insertion loss than a cable with a small OD (such as 28 AWG cable). Because insertion loss levels are higher in smaller-diameter patch cords, additional de-rating is necessary.
|Example of 28 AWG Patch Cord Usage|
|28 AWG Patch Cord Length||Maximum Perm. Link Length||Resulting Channel Length|
|6.2 m (20.2 ft)||90 m (295.3 ft)||96.2 m (315.5 ft)|
|10 m (32.8 ft)||82.5 m (270.7 ft)||92.5 m (303.5 ft)|
|15 m (49.2 ft)||72.8 m (238.7 ft)||87.8 m (287.9 ft)|
Cable insertion loss limits are determined by multiplying applicable horizontal cable insertion loss requirements by a de-rating factor of 1.95. This allows a 95% insertion-loss increase to account for smaller wire gauges and design differences.Because the de-rating factor for a 28 AWG patch cord is 95%, it’s 95% more “lossy” than a horizontal cable of the same length.
We’ll keep you updated as the appendix to ANSI/TIA-568.2-D is released so you’ll be one of the first to know when 28 AWG cable is officially included in the standards. Make sure to subscribe to our blog updates so you don’t miss it!
Ron joined Belden in 2016 to help define the roadmap of technology and applications in the enterprise. Prior to this, he developed cables and connectivity for Panduit and Andrew Corp. Ron Tellas is a SME in RF design and Electromagnetic Propagation and has BSEE from Purdue University, a MSEE from IIT, and a MBA from Purdue University.