The cable guys

Without doubt, future generations of installers will refer to the present time as the ‘age of communications’.

We have reached the stage at which standalone security technologies and installations are becoming increasingly rare, having been replaced by integrated systems and enhanced by the addition of communication networks.

As a result, a new generation of cables have become available to the security installer.

The importance of installing the correct cables is well known, as the actual wiring in the walls is generally the most time consuming and costly part of any installation. The cables to be used are always recommended by the manufacturer to link their equipment and components, or in networking they are specified by the IT specialist.

With this in mind, let’s look at the overriding factors involved in a security installer using hard wired electrical cables, and take an overview of the more practical elements of cable construction and the reasons why we install a specific cable type.

This will not only give us the chance to appreciate why particular cables are selected, but it will also enable us to question the judgement of others if we feel that a better wiring option exists.

Conductor type
The most popular material for actual conductor medium is copper. In relative terms, it has low electrical resistance, is not unduly affected by corrosion, is not heavy, has good qualities of strength and is economic. Gold, silver, steel and aluminium cannot compete in the overall scheme of things.

The conductor is available as either stranded or solid core. Stranded cable is the more flexible, and can be easily installed and routed through awkward points. It is therefore used to great effect as the predominant cable in all mainstream intruder alarm systems, and is also used for patch cables around equipment.

Stranded cables do suffer from greater power losses than solid core, as the current flows through the resistance of the conductors. However, this is not a consideration in intruder signalling or in those systems which only involve low values of voltage or content.

Solid core is a better conductor for long runs and if attenuation (power loss) is seen as a distinct problem, but it can harden and break if heavily flexed or continuously adjusted. It is used in many telecommunication applications and for general fixed wiring.

It should be noted that as the temperature of the cable increases, the resistance of the conductor also rises. For this reason, cables must be protected when running through areas that can be subject to high ambient temperatures.

Cable construction
The cable in its simplest form is a copper conductor held within its length by an insulator. But security cables carry data, and when connected to sensitive equipment need additional features added to counter the effects of external interference.

Because the changing currents in other cables in the same general area create a changing magnetic field, this can be induced as electromagnetic waves in the form of electromagnetic interference (EMI) into our security cables. EMI in our systems distorts the current flow, and can result in system crash or memory erasure.

For this reason, specified cable has the actual conductors insulated and wrapped in a conductive medium of copper or aluminium foil, metal tape, braid, or even a sleeve. This protective medium shields and protects our cable from EMI.

At the time of installation, by connecting the shield to a good earth ground point, the EMI that may have been induced into it is able to leak away. Often a copper drain wire is run with foil along its entire length, as it provides an easy way of making the earth connection at the cable ends.

Most organisations are only given an opportunity to cable a building once every seven to ten years, so the specification for wiring must be onerous

A plastic or fibre rip-cord may also be included to help the jacket to be stripped back. Although EMI is the main problem encountered, the foil or braid is also able to give a measure of protection against other induced electrical fields.

Twisted cable
For standard signalling cable, the conductors run parallel with each other throughout the cable length. But many specifications now call up twisted cable.

These are available in an enormous range of variants. Twisted pair cables are twisted along their length, with one of the pair conductors carrying the signal and the other operating as the return path.

The twisting of wires greatly reduces the effects of EMI, as the interference induced into it acts in opposite directions. Copper unshielded twisted pair (UTP) is presently the dominant cabling medium in building data networks.

Data transmission
In regard to the sending of data, telecommunication speeds have increased enormously over the last few years, and will continue to do so. The bandwidth of a system governs how fast information can be transmitted over the communication links, and the cable has a major role to play in coping with the speed of data transmission.

The cables we use are known by the Categories 1 to 7 or the international groups Classes A to F, with 1 and A being at the lower end of the scale in terms of bandwidth.

In practice, the most popular cables we currently use are Category 5e (enhanced) and Class D, as the lower categories are obsolete, or relatively ‘slow’. Taking this a stage further, Category 6 copper cabling systems are claimed to be compatible with fibre optic links in terms of speed.

Installers are involved with a huge a variety of cables, including electrical installation, flexible mains, data transmission, audio/visual, signal, telephone, co-axial and screened. Although certain systems are clearly defined in terms of acceptable cables, such as fire detection and emergency lighting, not all of the systems in which we have an interest are so established, so cable selection must take many aspects into account.

Unfortunately, most organisations are only given an opportunity to cable a building once every seven to ten years, so the specification for the wiring must be onerous. The points in table 1 can be applied in the selection process.

Installation
During the fitting of the cables, the security installer must take into account segregation of the security cables from the other services and the need for supports.

In the absence of any specific fixing requirements being quoted for installed cable in accessible positions, table 2 can be used as a guide for the spacing of supports for all copper cabling systems.

Radio frequency wireless systems will continue to make inroads into all of our system types. But what we also know is that presently in many applications there is no option but to install copper cables.

With that thought in mind, we have an obligation to understand just why a particular type has been specified in the first place.