Performance under real-world interference
1. Electromagnetic compatibility (EMC)
In a typical office the worst offenders are LED drivers switching at high dV/dt and 4 G/5 G small-cell repeaters splashing RF across 700 MHz-3.5 GHz. A well-installed F/UTP cable shows 15–20 dB better coupling attenuation than U/UTP in that band – enough to turn a marginal 10 G-BASE-T link into a rock-solid pass on your field tester. In anechoic-chamber trials ACCL ran for a medical client, Cat 6A U/UTP links next to 2 kW MRI gradient-amp cables failed return-loss limits at 500 MHz; swapping to U/FTP solved the issue without rerouting containment.
2. Alien crosstalk
Category 6A raises the test frequency to 500 MHz, where pair-to-pair and cable-to-cable coupling becomes the top failure mode. Individual pair shields in U/FTP and S/FTP designs dampen that coupling so installers can run tighter bundle counts. That directly affects PoE heat budgeting because fatter bundles trap more heat – shielded cabling lets you achieve the same port density with lower temperature rise.
3. PoE stability
High power over Ethernet draws continuous 600 mA per pair. Unshielded cables act like long antennas, emitting common-mode noise that back-feeds into sensitive audio and control lines. A continuous aluminium foil coupled to a low-impedance earth starves that antenna action. In our Cabling Fire Safety audits we routinely measure 3–5 °C lower bundle temperature on F/UTP versus U/UTP when both run 90 W PoE++.
Cost, installation and maintenance – the bits the brochure glosses over
Material price. Shielded Cat 6A typically lands 10-15 % higher per metre than unshielded. Once you add shielded modular jacks and controlled earthing hardware, the premium can approach 25 %.
Termination time. Modern tool-less shielded jacks have closed the gap, yet crimping the drain wire, folding the foil and closing a metal housing still add perhaps 30 seconds per outlet. On a 2 000-port floor that equates to an extra day of labour.
Bonding and grounding. A shield does nothing unless it is bonded to the building’s supplementary bonding network (SBN). BS EN 50310:2020 stipulates ≤0.2 Ω impedance back to the main earth bar. Poorly executed bonds can create earth-loops that inject more noise than they remove. If you choose STP, budget for proper earth bars and refer to our guide on equipotential bonding.
Connector mix-ups. Field staff sometimes mate UTP patch leads into STP panel ports, breaking the shield path. ACCL avoids that by colour-coding cords – grey for UTP, black for STP – and including it in the Data-Cabling Audit checklist.
Standards and accreditation – why “Category 6A” alone is not enough
ISO/IEC 11801 and BS EN 50173 treat shielded and unshielded systems as peers provided each passes its own performance class. That means a U/UTP channel can achieve Class EA just as an F/UTP can. Where shielded wins is coupling attenuation (aCa) and transfer impedance (ZT) – parameters the standards allow but do not mandate for compliance. Savvy specifiers therefore add these values in the Employer’s Requirements so contractors cannot down-spec after contract award.
For PoE++ projects you should also cite IEC 60512-99-002 (mating-cycle current-carrying capacity) because high current plus poor shielding equals melted connectors in worst-case fault loops.
