CCTV—Which Wire Should You Use?

Coaxial cable: Coax is good for short wire runs in low-noise environments. Its thick copper construction yields low signal losses. As an unbalanced transmission-line, its interference immunity is poor compared to that of balanced twisted-pair cables and...


Coaxial cable: Coax is good for short wire runs in low-noise environments. Its thick copper construction yields low signal losses. As an unbalanced transmission-line, its interference immunity is poor compared to that of balanced twisted-pair cables and it has no ground-loop immunity. Coax doesn’t fit in with “structured cabling” standards such as EIA/TIA568B and will not natively support IP (ethernet). It is bulky, expensive and has limited flexibility and bendradius. Termination (connectorization) is more difficult, time-consuming, and costly. Separate wire pulls are required for camera power and/or RS-485 telemetry.

Siamese cable: This cable is a coax with attached power conductors. The result is fewer installation pulls. This wire is more bulky than coax and more expensive. All other coax considerations apply.

UTP cable: Offering the lowest cost of all, it is most immune to interference, smallest diameter and easiest to terminate. It also meets EIA/TIA568B structured building wiring standards, allowing it to be used for video, telemetry, camera power, voice, IP/ethernet. Performance varies from voice-grade to gigabit (Category 6), and any category-rated UTP may be used for video.

Untwisted conductor cable: Susceptible to interference and should not be used for video applications.

FTP and STP cable: This foil or braid shielded cable is designed for datacom environments. Before using it, check its data-sheet for parasitic capacitance, also called “mutual capacitance.” With special exceptions, this value should be below 20pF per foot. STP wire should never be used for passive-to-passive video.

Multi-pair cable with an overall shield: This cable is suitable for video transmission provided there are six or more pairs in the bundle. Fewer pairs means that the shield is close to each wire-pair with resulting elevated capacitance. Check the specificiation sheet.

Copper-plated steel: This looks just like Category 5. It is not suitable for datacom applications but may be used at short distances in passive-to-active video applications.

Although not nearly as broad as the choices for cameras, there is still wide open selection when it comes to choosing the proper wire for CCTV. Selecting the correct wire can result in crisp clear video, low material and labor cost and a clean future-ready installation. The wrong wire can be costly, deliver a noisy and/or blurry picture, waste valuable time and cause embarrassment. Here are the prevailing characteristics you should look for in deploying the proper wire for CCTV:

Interference immunity: Coaxial is an unbalanced transmission line and is susceptible to interference. Technicians should avoid placing it near noise sources such as power cables. Unshielded twisted pair (UTP) [and its cousins, foiled twisted-pair (FTP) and shielded twisted-pair (STP)] are balanced transmission lines. They are inherently immune to interference.

Ground loop immunity: Coaxial has no ground-loop immunity and can suffer from “hum-bars” in the image. UTP with passive-to-passive transceivers is slightly better, however UTP with passive-to-active transceivers produces hum-free transmission every time.

Low frequency attenuation: At low frequencies less then 100KHz, the only thing that matters is wire resistance.Thicker conductors yield lower losses, visible as picture brightness. Coax has slightly better low-frequency performance than UTP wire.

High frequency attenuation: At high frequencies greater then 1MHz, copper losses are dwarfed by inductive and capacitive parasitics. These losses can be substantial and are the dominant limit to distance, showing up in the image as soft detail or loss of color. A good receiver can boost these frequencies, delivering a flat frequency response. The result is “lossless” transmission that delivers detail.

Plenum versus non-plenum cable: Plenum-rated wire is typically teflon-based and is used within buildings where toxic gasses released during a fire could enter ventilation systems.

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