Yvonne Butterworth, ADI-Gardiner intruder product manager, says installers should avoid allowing cable to be the weakest link in their systems – because if it is, a fault is very difficult to find, and very expensive to put right…
We are all quite correctly obsessed with meeting the tighter specifications for intruder systems and products, as most recently has been the case with PD6662, yet we seem to ignore that most universally used product in all installations – good old security cable.
'Cable is cable, one is just as good as another' is one of the most repeated phrases I hear among installers. Not only do I doubt that was ever true, but it is certainly not the case now!
There is a cable standard for a very good reason. BS4737 Part 3 is designed to approve a cable with the minimum of resistance, and therefore ensure the effectiveness of the system and reduce the incidence of false alarms due to signal drop.
Security cable might not appear to be the most sophisticated of , yet its characteristics are absolutely vital to the efficiency of the installation. If inferior product is used, it can easily by an unwelcome cause of false alarms.
The BS4737 Part 3: Section 3.30 specification for components is THE specification for PVC insulated cables for interconnecting wiring, and specifies clearly the conductor resistance and construction, along with PVC shrinkage, type and thickness, and minimum of resistance.
Should any of these parameters be compromised, the system's integrity can be jeopardised. As a result, false alarms and expensive call backs can occur.
The recent dramatic rises in the price of copper, the main conductor used in security cabling, coinciding with the increasing system demands of PD6662, have put the quality of security cable firmly back on the agenda within the industry.
There may inevitably be some cables offered which claim to meet BS but simply do not. And there is also security cable on the market which may not claim compliance with BS4737, but offers some small commercial advantage. The question is, is it worth the risk?
Lower costs for non-BS cables are often reflected by the reduction in the amount of copper used in the cable, and the absence of tinning, which is a process to assist good termination. It can also be reflected in the conductor used, which may be a low grade copper, or an alternative composite conductor material with significantly different characteristics.
The UK market has for many years taken the specification and availability of security cable manufactured to BS4737 as the standard for all quality installations, but don't take that for granted – not in today's competitive marketplace. Don't let the cable be the weakest link in your installation – always use cable manufactured to the British Standard.
Standard cable
This cable is based on cores made from seven strands of 0.2mm annealed tinned copper wire and is sheathed in Type 1 PVC. This cable is available in white or brown.
Low smoke and fume cable
The standard security cable can also be specified with special low emission PVC outer sheathing. Using this sheathing, the compound oxygen index level is greater than 32 per cent. This means it will require more than 32 per cent of the volume of air to be oxygen for it to catch fire. 'Normal' air contains around 19 per cent oxygen. A normal PVC sheathing compound would give a figure of 20 per cent.
14 strand cable
This is similar to the standard cable except that each core is made up of 14 strands of 0.2mm cable. This gives a nominal conductor area of 0.44mm sq. This is often used in areas where 0.5mm sq wire is required.
Screened cable
This uses the same cores as standard cable. In addition, an aluminium foil is wrapped around the cores. Screened cable offers significant advantages in situations where RF interference or spurious signals may lead to false alarms or erosion of data. An earth drain wire is present along the entire length of the cable, providing shield continuity and a convenient earthing point at the control panel.
Twin power and data
Two different conductor types are used. A power pair (red/blue) is provided in 16 strands x 0.2mm (0.5mm sq) for use where higher than normal current carrying capacity or lower voltage drop is required.
The data cores consist of the standard seven strands x 0.2mm tinned copper wire. The data cores are aluminium foil wrap screened (with an earth drain wire) to give added protection against induced transients that may be carried via the power cores or outside influences.
Twisted pair cable
Each core consists of 24 strands of 0.2mm (0.75mm sq) copper wire. Each pair of cores is twisted and aluminium foil wrap screened. A bare seven strands x 0.2mm earth drain wire is included. Twisted pair cable is particularly useful for bus systems or for installations requiring longer lengths of cabling such as access control and CCTV.
New guide to cable standards published
Anixter has published a new cabling standards guide.
It draws on Anixter's extensive knowledge of the cabling industry and brings together important information on the latest cabling standards for voice, video and data networks in wired and wireless environments. Anixter this ensures customers have a quick and convenient way of checking their installations are installed correctly and conform to internationally recognised standards.
In addition, the guide provides facts about the most efficient "network topology", including details on multi-vendor and component interoperability and maximum cable lengths.
The guide is available to order at www.anixter.com/standardsguide.
Source
Security Installer
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