Hi,

The benefit of a shielded cable is EMI control and a more pristine environment for the Twisted Pairs in the cable bundle. The shield provides immunity to power line and reception of other radiated noise from the surrounding environment. This provides a more error free connection for all nodes as the network is not clogged with transmission errors due to a susceptible cable on the network. It also contains emissions that may affect other devices or receivers in the home.

This works only if the connectors AND the equipment you connect to (both ends) include the mating connectors that provide the shield connection.

The shielded RJ-45 cable connectors are made to allow the shield to be terminated to a metal shell that surrounds at least 3 sides of the RJ-45 plastic connector. This mates with wiper fingers in the end user equipment that they are connected to.

If the shield is not terminated on both ends, it forms a mono-pole antenna and with the length of cables in the wall, it will have no trouble radiating noise with activity on the cable to nearby cable receptors and antennas. Same thing with UTP cabling.

There are a few inherent problems with shields though. One is that they introduce additional capacitance from the conductor pair to the shield which can sometimes reduce data rates or cable length for a given data rate (50m instead of the 100m specification). At 10Gbps it may make a difference or not. Another problem with STP is that a foil shield can break if the bend radius is exceeded (going around tight bends in the walls), which results in a compromised shield (cracked), or open shield. A braid shielded cable is much better for this but some of the cable connectors are not designed for braid (many are for foil and drain wire termination - FTP). At frequencies above 1 MHz or edge rates faster than 1 us the shield needs to be terminated on both ends for proper EMI control and Signal Integrity.

If you poorly terminate the connector and do not preserve the twist (resulting in reflections and Near End Crosstalk - NEXT), you might have problems. At 10Gbps you may also have to deal with Alien Near End Crosstalk (ANEXT) with adjacently routed cables. ANEXT is caused by noise coupled from adjacent cables. With many cables in the walls near each other, or near a common server, this could be a real problem. The CAT-6a STP prevents this problem.

They make a foil shielded twisted pair cable (S/FTP or PiMF) where the four individual twisted pairs are individually shielded and there is a braid overshield similar to the Cat-7 cable mentioned above. This would be the best choice for your upgrade if it is cost effective.

Despite the difficulties with shielding, I would recommend it. The recommended path for commercial and industrial upgrade is to STP cables to avoid ANEXT, provide a controlled environment for the transmission/reception media, and reduce EMI emissions and susceptibility.


BTW, my understanding of STP is that the individual pairs within the bundle do not have a separate shield for each pair, just the overall cable that goes to a connector has the shield. In other words, the TX/RX pairs are unshielded and the overall cable has the shield. Some manufacturers indicate STPs (individually shielded pairs) within an overshielded cable as double shielded. To me that also might mean a foil and braid overshield shield, or 2 over braids separated by mylar (to obtain additional magnetic shielding properties). However I commonly refer to STPs or TSPs (same thing) as a single twisted pair with a single shield.

Good luck with your decision.

Ross