Putting you in the picture
Some years ago the security industry was inundated with wireless radio frequency security products. So why are cables still so important?
The short answer is that in the majority of cases, cable is simply more reliable. For example, coaxial cables are commonly used in CCTV applications in many different forms, from RG59 and URM70 to satellite cables such as CT100 and CT125. Coaxes have the advantage of being understood by most installers and are relatively cheap and easy to terminate. They are also robust and readily available in many different versions. However, the disadvantage of coaxial cables is that the signal quality can diminish as the run length gets longer. To overcome this, larger, 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 security cameras, composite coax cables with a mix of power, signal and coax or twisted pair data cable combined in one jacket are increasingly popular.
Other composite cables are available 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; particularly 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 for example.
Structured wiring
Many cameras are now IP enabled and 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. FS Cables now stock Cat-5 in coloured jackets so circuits can be easily identified; for example, all security cable runs in green Cat-5.
It is important to avoid any CCA (Copper Clad Aluminium) cables as signal losses are much higher than pure copper and conductors can be prone to breakage at the point of termination.
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 CCTV picture up to 100m. RG59 and URM70 can carry pictures up to 250m while RG11 extends to a distance of 600m. CT100 is around 450m with CT125 up to 650m. A recent test on good quality Cat-5 worked well at 600m.
Sheathing materials
It is not uncommon now to find security installations which, as well as internal runs, require cables to be clipped externally to masts or buildings or pulled through ducts. 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 low risk 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 and polyethylene (PE) sheathed to protect against the ingress of water
• SWA – Armoured to protect against physical damage
PVC
PVC is the cheapest option for a given cable design because 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.
LSHF
Low Smoke Halogen Free (LSHF) compounds are an alternative 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 retardant qualities are much better. They tend to be stiffer and more expensive than PVC, but prices are coming down as more and more clients are specifying LSHF cables at the design stage.
Duct grade
Duct grade cables combine the same internal components, (conductors, cores and insulation, together with screens) but with the added protection of a heavy, black, UV resistant, waterproof, PE jacket. Good quality duct grade cables retain the standard PVC inner jacket for added protection and faster and easier termination. The PE jacket not only protects the cable from moisture but also adds to the physical strength of the cable, which is important when the cable is pulled through ducts, sometimes over hundreds of metres. Duct grade cables are also ideal for exposed external installations where the jacket gives both mechanical and environmental protection as PE offers very good UV resistance.
Armoured cables
SWA (Steel Wire Armoured) cables give the ultimate level of 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 or rodent damage.
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