CCTV cabling putting you in the picture
Some years ago the security world was inundated with ‘wireless’ radio frequency security products ranging from detectors to cameras. So, why 20 years on are cables still so important?
The short answer is that, in the majority of cases, cable is better and more reliable and it comes in all shapes and sizes to meet the needs of most applications.
Coaxial cables
Traditionally, coaxial cables were used by security installers. They are now commonly used in CCTV applications in different forms, from RG59 and URM70, to satellite cables such as CT100/125. Coax is understood by most installers and is also relatively cheap and easy to terminate.
The disadvantage of coax is that signal quality can diminish as the run gets longer. This means that more expensive coaxes are needed. Also, the signal can be prone to interference in ‘high noise’ environments such as near motors, power lines or fluorescent lighting.
Composite coaxial cables
With the increase in infrared illumination for night-viewing and the need for Pan/Tilt/Zoom (PTZ) functions on cameras, composite coax cables with a mix of power, signal and coax or twisted pair data cable combined in one jacket are becoming increasingly popular.
Applications include remote cameras situated away from the main installation such as in car parks or on roadside cameras where the cable is run over a series of pulleys, enabling the camera to be lowered for servicing or cleaning.
Other composite cables are available ‘shotgun style’ where the element, coax, power and signal are run parallel to each other but joined by a web.
Composite cables for specific security systems are also popular, in particular for door entry phones, access control units and retail identification systems. A coax combined with multiple signal and power cores make for a quick, simple installation on video entry systems.
Structured wiring
More cameras are now able to transmit over twisted-pair cabling instead of the conventional coax. Twisted pairs, normally unscreened (UTP) of the Cat-5 variety are widely used to flood wire buildings and it often makes sense, when installing a network, to incorporate the CCTV element of the security system within it.
The main things to consider when using Cat-5 are the relatively delicate nature of the cable in its standard form and the possible increased cost of cameras and multiplexers required on the network. Standard Cat-5 is delicate and to avoid signal loss must not be trapped, crushed, kinked or bent too tightly around corners.
As a broad comparison - and these figures are approximate and can be affected by many other factors - CW1308 internal telephone cable will give a reasonable picture up to 100m. RG59 and URM70 can carry up to 250m while RG11 extends to a distance of 600m. CT100 is around 450m with CT125 up to 650m. A recent test on Cat-5 worked well at 600m.
Sheathing materials
Nowadays it is not uncommon to find security installations which require cables to be clipped externally to masts or buildings or pulled through ducts. As external applications and the physical demands that these cables are being asked to cope with are increasing all the time. The question for security installers is to look at the application and decide on a suitable grade of cable for the job.
Popular cable grades include:
PVC – For internal installations.
LSHF – Normally for internal installations in sensitive areas, where there is a threat to people or property in the event of fire.
Duct grade – Popular in external installations. PE sheathed to protect against the ingress of water.
SWA – Armoured to protect against physical damage.
PVC is the cheapest option for a given cable design, it offers good flexibility, low cost and reasonable durability. The disadvantages are that some grades of PVC can weather badly and give off poisonous gases and fumes when burnt. Data and signal cables in some cases are prone to physical damage if badly handled.
Low Smoke Halogen Free (LSHF) compounds are similar in appearance to PVC cables but behave very differently when exposed to fire. They do not give off significant amounts of toxic fumes or smoke and often their fire retardance is much better. Disadvantages include stiffness or inflexibility and a higher price than PVC although prices are coming down as more and more installers are specifying LSHF cables at the design stage.
Duct grade cables combine the same internal components, (conductors, cores and insulation, together with screens) with the added protection of a heavy, black, UV resistant, waterproof, polyethylene (PE) jacket. Good quality duct grade cables retain the standard PVC inner jacket for added protection and faster and easier termination. The PE jacket protects the cable from moisture and adds to the physical strength of the cable.
Duct grade cables are ideal for exposed external installations where the jacket gives both mechanical and environmental protection as PE offers very good UV resistance. Clipping to masts, running up the sides of buildings, across roofs or on catenary wires are common applications, as are installations in schools, industrial yards and CCTV networks. Disadvantages include a larger diameter and bend radius and relative stiffness when compared to PVC.
SWA are similar to duct grade versions but give greater protection. The armouring process takes a standard or duct grade cable and lays galvanised steel wires of 0.9mm or 1.2mm diameter and an oversheath of PVC, PE or LSHF to give the cable total protection.
Whereas armoured cables were traditionally used for direct burial they are now increasingly popular solutions for protecting cables against vandalism.
A wealth of solutions
The choice of cables on offer today is increasingly diverse and is suitable for almost every security installation and application. Despite the growth of wireless technology in security the future for cable still looks secure!
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