Serie 101: Trenzado frente a Latiguillos sólidos

21 de agosto de 2019 / Serie 101

You’ve likely heard copper patch cords referred to as being constructed of either “stranded” or “solid” cable, but do you know the difference and which to choose when? 

Just like the name implies, stranded four-pair cables are cables where each of the eight conductors of the four-pair cable are constructed of multiple “strands” of wires wrapped around each other, while solid cables are constructed with just one solid copper wire per conductor.

In a stranded cable, the wires that form the conductor are typically very thin wires that are wound concentrically in a helix to form the conductor (think of this like a rope). The construction of stranded cable is specified as two numbers – the number of strands as the first number and the gauge of the strand as the second number. Por ejemplo, un 7X32 (a veces escrito 7/32) indica que hay 7 hilos de alambre calibre 32 AWG que conforman el conductor. In contrast, solid cable will just include one gauge number to indicate the size of the conductor.

But aren’t stranded and solid cables of the same category type the same gauge size? Yes, indeed they are. That’s because the final conductor size, regardless of whether it is made up of multiple strands or one solid conductor, are the same. En otras palabras, un cable 24 AWG sigue siendo un cable 24 AWG.

How Do they Differ?

The key physical difference between a stranded cable and a solid cable is flexibility. Stranded cables are much more flexible and can withstand more bending compare to rigid solid conductors that can fail if flexed too many times. And the more strands a conductor has, the greater the flexibility. Strand count can also impact cost – the more strands that make up a wire, the greater the cost. To keep costs down, stranded twisted-pair cable uses a high enough strand count to maintain proper flexibility but not so many that it creates a dramatic price difference. In other words, it’s a careful balance between cost and flexibility.

The construction of the cable also impacts termination. IDCs on jacks, patch panels and connecting blocks are made for solid cable. The individual conductors of a solid cable will hold their shape and properly seat in the IDC, while stranded conductors will typically break and can come loose over time. Solid wire is also considered more rugged and less susceptible to corrosion since it has less surface area than a stranded wire.

Another key difference is electrical performance. Solid cables are better electrical conductors and provide superior, stable electrical characteristics over a wider range of frequencies, offering lower susceptibility to high-frequency effects and lower DC resistance than stranded cables. That’s precisely why TIA standards allow a 20% increase in attenuation for stranded construction.

Which do I Choose?

When it comes to horizontal cable runs, there is no choice. Solid cable is the standard due to its better electrical performance and ability to punch down to IDCs . Where you do have a choice is with patch cords since most manufacturers offer both.

Because stranded cables are more flexible and can withstand bending, they make excellent patch cords for equipment connections and cross-connects where cables are frequently bent and manipulated. Patch cords are also shorter in length, so the higher resistance of the stranded construction is not typically a concern.

There is however a primary application in today’s LANs that warrants the use of solid patch cords – power over Ethernet. Cuando se entrega PoE a través de un cableado de cobre de par trenzado, parte de la potencia se disipa como calor. Cuando la potencia se disipa como calor, la temperatura del cable puede aumentar. With their higher DC resistance, stranded patch cords are more likely to exhibit degraded transmission performance at elevated temperatures.

Aunque normalmente no constituye una inquietud en espacios con control ambiental como la sala de telecomunicaciones, una vez que empiece a conectar dispositivos en el cielorraso (piense en puntos de acceso inalámbricos, cámaras de seguridad y luces LED), los latiguillos trenzados podrían ser un problema. A good rule of thumb is that if the environment is not temperature controlled and there’s not a lot of manipulation going on, choose a solid patch cord. If you do use stranded patch cords in uncontrolled environments, you’re better off keeping them short (about 5 meters or less). And if you’re skeptical, check it out yourself. Fluke Network’s DSX Series Patch Cord Test Adapters can be used to test copper patch cords or you can see the difference in channel testing.

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