Posted by: Paul Kish on August 07, 2014
As a follow up to last week’s blog on Bonded-Pair patch cords from guest blogger Greg Deitz, there is another issue of concern surrounding patch cords.
With some vendors touting smaller diameter patch cords with 28 AWG conductors as enabling easier cable management, optimum airflow, reduced pathway fill and potentially lower operating costs, some are questioning whether these smaller diameter cords are acceptable.
It’s time to set the record straight.
According to the TIA 568-C.2 standard, patch cord cables using 28 AWG conductors are not allowed. The standards 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 is necessary to reduce the total length of cords in a channel to a maximum of 8 meters from a maximum of 10 meters when using 24 AWG cords. This is because of the higher Insertion Loss de‐rating factor of 1.5 for 26 AWG cords 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.
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 remote power of devices using PoE.
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 that is 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 Plus standard can deliver up to 25.5 Watts of power over 2 pairs. As more PoE Plus 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 49 Watts, and the potential for up to 80 Watts 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.
If you’re considering smaller diameter patch cords with 28 AWG conductors, think again.
Belden does not recommend or offer equipment cords, patch cords or work areas cords that are not compliant with the standards. We also do not recommend cords that are not suitable for remote powering applications, have significantly higher signal losses and are more susceptible to damage due to mechanical stresses.
What we do recommend is exactly what Greg covered in last week’s blog. Our 24 AWG Bonded-Pair patch cords 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.