Shielded VS. Unshielded Cabling
In copper structured cabling system at all levels, there are two main network cable technical types: Shielded and Unshielded cabling systems. Both types have been in existence since the earliest cabling standards were defined. Shielded cabling using shielded cable became popular from the outset in countries like Germany, Austria, Switzerland and France, while U/UTP was quickly adopted in the rest of the world. Although both systems work fine at 1 Gigabit Ethernet data rates, shielded systems can demonstrate superior performance at higher data rates such as 10G due to their ability to reliably support higher frequency transmission.
What Is the Function of a Shielded Cable?
F/UTP Shielded Cable
F/UTP cable shielding structure: Four pairs of wires in the data cable have a layer of aluminum foil shielded, this layer of shielding (also called screening) protects against EMI/FRI and crosstalk.
S/FTP Shielded Cable
In S/FTP structure, in addition to the braided foil shield, the four twisted pairs have a layer of aluminum foil shield respectively to protect the transmission signal and make sure they do not interfere with each other, making near-end crosstalk attenuation (NEXT) performance dramatically good. Better NEXT performance means higher SNR and better transmission quality and faster system output. S/FTP shielded cables’ excellent NEXT structural performance can not be compared by other cables (such as non-shielded U/UTP). Therefore, ISO11801 on the Cat7 cable (600MHz) and Cat7a (1000MHz) only provides the S/FTP cable structure, U/UTP cannot meet.
10GBase-T Makes Data Cable Face New Problem: Alien Crosstalk
2006 Copper Gigabit Ethernet applications published the proposed new standard transport protocols 10GBASE-T. Compared to 1000Base-T, its transmission rate increased 10 times. 1000BASE-T copper cabling has requirements for parameters (Attenuation, NEXT, Return Loss, etc.). The bandwidth required to reach 1-100MHz with UTP Cat5e (Class D) cabling system. 10GBASE-T cabling channel requirements of all component parameters have to be up to 500MHz bandwidth, which requires copper to reach at least Cat6a (Class Ea) or higher level.
Along with the development of 10GBASE-T, external noise problems become more evident, resulting in a specification for external noise to be used to assess in the same bundle of cables, the interaction between different cables. This is what we call Alien Crosstalk. Alien Crosstalk will increase with the increase of frequency. Worse, 10GBASE-T confronted with external noise, will not be able to “adaptive” to lower the rate at which the network may be subsequently face paralysis. Therefore, to support 10GBASE-T cabling system application, the ability to resist alien crosstalk is vital.
Since 10GBASE-T high transmission frequencies and complex coding method is very sensitive to the external noise. Shielding system excellent coupling attenuation performance makes it naturally have to resist alien crosstalk. The unshielded system against alien crosstalk is usually only on the performance of 0dB. Shielding system in the design completely satisfies the application of 10G.
The Installation of 10GBase-T: U/UTP VS. FTP 80a
As far as possible away from power cable during installation. Different applications (1Gb/s and 10Gb/s) in the same pipeline transmission will cause the external crosstalk.
The advantages of using a shielding system can be technically proven by different complex parameters such as coupling attenuation, shielding efficiency and transfer impedance. But from a user’s point of view, what makes the most sense is the practical advantage of a shielded cable-based cabling solution in the ever-increasing world of high-speed network applications. The advantage of shielded cables over UTP cables is that they are aimed at deepening the effects of EMI caused by the widespread use of electronic devices. Moreover, an increase in the rate of network applications means that the network is more sensitive to EMI.
The Separation Distance Between the Data Cable and Power Cable
EN50174 standard defines the content of four different coupling attenuation value levels of data cable respectively from A (low coupling attenuation, worse) to D (high coupling attenuation, good).
Classification of information technology cables
|Coupling attenuation at 30 Mhz to 100 Mhz
|TCL at 30 MHz to 100 MHz
|Screening attenuation at 30 MHz to 100 MHz
|>= 80a dB
|>= 70 -10xlg(f) dB
|>= 85d dB
|>= 55b dB
|>= 60 -10xlg(f) dB
|>= 55 dB
|>= 40 dB
|>= 50 -10xlg(f)c dB
|>= 40 dB
|< 40 dB
|<50 -10xlg(f) dB
|< 40 dB
Installers need to know which cable separated levels to determine the choice of the data requirements of the standard cable with power cable between the minimum separation distance. Data cable coupling attenuation higher the value and power cables minimum separation distance between the smaller. Please refer to the following three examples, screenshots from Nexans Toolkit.
Example 1: U/UTP (Class B – Coupling Attenuation >/= 40dB) -> 225mm
Example 2: F/UTP (Class C – Coupling Attenuation >/= 55dB)-> 114mm
Example 3: S/FTP (Class D – Coupling Attenuation >/= 80dB)-> 24mm
Relative to the shielded cable, the unshielded (U/UTP) separation distance between cable and power cable is further. In the implementation of the project, if need the data cable and power cable isolation far distance, we need a bigger size pipe/bridge, or even additional bridge, doing this will no doubt have higher cost, sometimes limited to the bridge installation space. To make matters worse, these additional requirements are often neglected or ignored, making network system the key point of interference.
For shielded, unshielded systems and fiber optic cable, they all need to implement protective grounding. Because of the need to consider personal and equipment safety, therefore no matter adopt what kind of cabling system, the metal part of the system must be grounded. For the shielding system, also need to implement the functional ground.
Shielding system relative to the unshielded system has been greatly improved EMC performance. For Gigabit Ethernet applications, shielding against external interference effects is essential, and shielded cabling system had to meet the standards in the design of anti-alien crosstalk (A-XT) requirements, can effectively prevent the cable from the adjacent between the external crosstalk. Shielded cabling system with shielded cable adopted, properly grounded at both ends of the case, is superior to unshielded system in resisting external interference.
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