When it Comes to Cable, is Smaller Always Better?
Editor’s Note: This blog was originally posted on Aug. 7, 2014. As of June 20, 2019, it has been updated to include additional relevant links, more information about smaller-diameter cable and tips about when 28 AWG cabling may make sense.
With some vendors touting smaller-diameter patch cords with 28 AWG conductors that allow for easier cable management, optimum airflow, reduced pathway fill and potentially lower operating costs, some industry professionals are questioning whether these smaller-diameter cords are acceptable.
As with many things having to do with cabling, the answer here isn’t always black and white: it depends on the situation and application.
What Do the Standards Say About Small-Diameter Cable?
According to the ANSI/TIA 568-C.2 standard, patch cord cables using 28 AWG conductors are not allowed. The standard specifically states that cord cables shall consist of four balanced twisted pairs of 22 to 26 AWG solid or stranded conductors.
The standard also specifies length de-rating to accommodate a 20% increase in insertion loss for 24 AWG cord cables of stranded construction and other design differences. For smaller gauges, the total length of patch cords must be adjusted to comply with the channel insertion-loss limits.
The standard specifically states that, when 26 AWG cords are used, it’s necessary to reduce the total cord length in a channel to a maximum of 8m from a maximum of 10m when using 24 AWG cords. This is because of the higher insertion loss de-rating factor of 1.5 for 26 AWG cords as compared to 1.2 for 24 AWG cords.
While the de-rating factor is not specified, 28 AWG patch cords have even higher insertion loss and could require as much 100% de-rating.
Why Does Cable Diameter Matter?
While patch cords with 26 AWG conductors can be used for non-powered equipment connections with the appropriate length de-rating, smaller-diameter patch cords with finer-gauge conductors are not recommended for PoE applications.
The high conductor resistance of the smaller gauge generates a lot more heat, which can cause the conductors to fuse or exceed the temperature rating of the cable at higher power levels.
For the same power delivery, a 26 AWG pair consumes 60% more power than a 24 AWG pair, and a 28 AWG pair consumes 150% more power. The energy wasted in heating the conductors is also power that does not reach remote powered devices, such as wireless access points, network cameras or IP phones.
Power-sourcing equipment that complies with the IEEE 802.3at PoE+ standard can deliver up to 25.5W of power over two pairs. As more PoE+ powered devices begin to show up in the LAN, smaller-diameter patch cords become an even greater concern. And there is a new 4-pair PoE standard under development for powering remote devices with up to 49W, and the potential for up to 80W at the highest power levels are being discussed.
Furthermore, with smaller-gauge conductors, there is a greater chance of broken conductors that can cause opens from stressing, flexing or pulling the patch cords.
What Does Belden Recommend?
If you’re considering smaller-diameter patch cords with 28 AWG conductors, it’s important to consider the application. Do these smaller-diameter patch cords make sense for every situation? They do not. But they may serve as a solution for certain environments.
In small and crowded spaces that deal with congested pathways and insufficient equipment space, data center managers often struggle with how to manage cable bulk in high-density patch panels. Because they’re significantly smaller than 24 AWG cabling, 28 AWG cables can help increase pathway capacity and allow for layouts that accommodate higher density. This could help you by improving airflow, port visibility, cord management and space utilization in racks.
But it’s important to note: The 28 AWG conductor size is outside the range specified in ANSI/TIA-568-C.2. This conductor size also does not support a 100m channel. There is, however, 28 AWG cabling available that does comply with the ANSI/TIA-568-C standard’s patch cord performance requirements (near-end crosstalk and return loss).
Belden does not recommend equipment cords, patch cords or work-area cords that are not compliant with ANSI/TIA standards. We also do not recommend cords that have significantly higher signal loss, are more susceptible to damage due to mechanical stress or aren’t suitable for remote-powering applications.
We believe that the most dependable, high-performance and reliable solution is Belden’s 24 AWG Bonded-Pair patch cords, which give you the flexibility of a stranded patch cord without needing to worry about length de-rating or the ability to support higher PoE wattage. But if these aren’t an option, 28 AWG patch cords may be a solution worth considering.
Have questions about whether 28 AWG cable is right for your application? Need help determining what might be a better option? Contact us today!