Coaxial, Specialty Media & Remote Powering

Beyond Twisted Pair and Fiber: Coax, Broadband, and Powered Media

Not every ICT design element is unshielded copper pairs or optical fiber. RCDDs still specify coaxial cable for legacy and broadband/CATV applications, and every modern horizontal design must account for Power over Ethernet (PoE), a transmission-media topic because delivered current, not just data, now travels the same cabling the RCDD specifies for signal transmission.

Coaxial Cable and Broadband/CATV

Coaxial cable consists of a center conductor, dielectric insulator, shield, and outer jacket, arranged concentrically (co-axial). Unlike balanced twisted pair's nominal 100-ohm impedance, coax used in broadband/CATV and video distribution is built to a nominal 75-ohm characteristic impedance (75-ohm coax such as RG-6 and RG-11 for video/broadband distribution; 50-ohm coax exists for RF/wireless antenna feeds, a different application). Coax remains relevant in RCDD scope for:

• Broadband/CATV distribution - video signal distribution within a building, still specified in hospitality, healthcare, and MDU (multi-dwelling unit) residential designs.
• Legacy and specialty systems - certain security camera, master antenna television (MATV), and building-wide RF distribution systems still rely on coax backbone.
• Termination via F-type connectors, with the RCDD specifying pathway separation and bend-radius rules similar to twisted-pair and fiber media.

Within the 75-ohm broadband family, the RCDD chooses between cable sizes based on run length and signal loss: RG-6 is the common, smaller-diameter, more flexible choice for in-building distribution and short drops, while RG-11 uses a larger center conductor and dielectric to achieve materially lower attenuation per unit length, making it the correct choice for longer trunk or riser runs where RG-6 attenuation would be excessive. Structured cabling standards increasingly favor twisted-pair or fiber (with IP-based encoders) over coax for new video distribution, but the RCDD must still recognize coax specification requirements for retrofit and hospitality/MDU work where legacy CATV plant exists.

Power over Ethernet (PoE): A Media Design Consideration

Because PoE delivers DC current over the same conductors carrying data, the RCDD must treat delivered power as a first-class design input, not an afterthought. The IEEE 802.3 PoE family has escalated across three generations:

PSE = power sourcing equipment (the switch or midspan injector); PD = powered device (the AP, camera, phone, or luminaire). Note the gap between PSE-side and PD-side maximums, that difference is the power lost to conductor resistance across the channel, which is why cable specification (gauge, category, length) directly affects how much power actually reaches the device. The newest 802.3bt Type 3/4 standards use all four pairs to carry current, reinforcing the Section 3.2 rule that all four pairs must always be terminated.

Bundle Heat De-Rating

Delivering real current through copper conductors generates real heat (I-squared-R losses), and that heat becomes a design problem specifically when many current-carrying PoE cables are bundled together in conduit, cable tray, or a tightly cinched bundle: heat generated by each cable adds to the heat trapped by its neighbors, raising the ambient temperature the whole bundle operates in. Higher conductor temperature increases conductor resistance, which increases attenuation and can push a marginal channel out of its category's performance envelope, independent of any change to the data signal itself.

TIA TSB-184-A addresses this specifically for PoE-powered horizontal cabling, guiding RCDDs to mitigate heat buildup through:

• De-rating maximum cable length below the standard 90 m permanent-link limit in large, high-power bundles
• Specifying larger-gauge conductors (e.g., 23 AWG rather than 24 AWG) to lower per-cable resistance and heat generation
• Limiting bundle size or providing better airflow/dissipation in conduit and tray fill calculations
• Accounting for worst-case ambient temperature in the space (e.g., a hot ceiling plenum feeding many PoE luminaires or cameras) rather than a nominal room temperature

This is a direct interaction between Chapter 3 (media) and Chapter 5 (pathways): an RCDD who correctly sizes conduit/tray fill per Chapter 5 but ignores PoE heat buildup can still deliver an underperforming, non-compliant channel. High-power, high-density PoE deployments, wireless AP fields, PoE lighting, and camera networks, are exactly the scenarios where TSB-184-A de-rating becomes a required, not optional, design step.

Remote Power Alternatives

PoE is not the only way to deliver remote power to ICT-connected devices. Traditional low-voltage DC power distribution, separate 12 V or 24 V conductors run alongside or in place of data cabling, remains common for devices such as access-control door hardware and legacy cameras, particularly where the load exceeds 802.3bt Type 4 limits or the device predates PoE support. For every remote-power approach, the RCDD confirms delivered voltage and current meet the device's requirements after accounting for cable-length voltage drop, and confirms the pathway and cable listing match the applicable life-safety code (NEC Article 725 for Class 2/3 power-limited circuits, Article 800 for communications circuits).

Exam Application

Expect scenario items that combine a media choice with a power or distance constraint: identifying whether coax or twisted-pair fits a hospitality MATV retrofit, calculating whether RG-6 or RG-11 fits a given riser distance, or determining whether a switch running 802.3bt Type 4 to PoE lighting on every port requires cable de-rating per TSB-184-A.