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Zoning and sectorisation of electrified perimeter fences

As the security director of the estate in which I live and with over 25 years’ experience in the perimeter electric fencing industry, I am regularly called out to assist on both our own estate and on neighbouring estates.

From these experiences it is clear to me that good access control, a comprehensive guarding service, monitored CCTV and a well-designed and well-constructed, monitored electric security fence are all crucial for an estate’s security.

During lockdown, residential estates experienced a surge in brash attacks on their perimeters and a marked increase in smash-and-grab tactics. What’s more, perpetrators have become more knowledgeable and a lot more tech savvy.

Criminals have realised that the response resources in large estates are limited and with limited guards covering large areas with many relatively poorly secured units and thus many potential targets, guards are unable to respond quickly. The perpetrators know this and so break into houses successfully using silent ‘cat burglar’ type tactics where they pilfer high value electronic items and are in and out of unsuspecting homes before the guards are aware and able to respond effectively.

The criminals have also found ways of using some electric fence systems to their advantage. They create a decoy short/alarm to send the guards to respond in one area while they actually infiltrate in another. Backing up the fence with CCTV is great, but unless the fence zones are trustworthy and correctly integrated with the CCTV, further confusion and misinformation can occur.

The speed and tactics criminals employ to cut the fence and roll over the wall means that sophisticated AI camera systems actually miss the criminal and even if they do capture some footage, this is often at the end of camera lenses or only in thermal footage which gives little detail. The perpetrator is also now in the estate and far from the perceived intrusion point.

The better the fence design and supplemented with old-school spikes, the better the perpetrator can be slowed down a bit and clearer footage obtained. Spikes and a monitored working electric fence also make it harder for the perpetrator to get out of the estate rapidly.

Old-school, high-voltage

It has become clear to me that old-school, high-voltage energisers powering as short a zone as possible is the most reliable and basic backbone for any large estate electric fence perimeter. Firstly, one must understand the difference between a zone and a sector. A zone is that portion of the monitored electric fence line that is powered by a single energiser. A zone can then be partitioned into sectors. Sectorisation is sold on the basis that it enables security personnel to accurately target their response to an alarm condition within a high-voltage zone.

There are basically three methods of monitoring an electric fence: monitoring the high-voltage circuit, monitoring the low-voltage circuit within a high-voltage network (below 50 Volts), or monitoring the current flow within the circuit.

The first and earliest method, still used successfully, is the simple monitoring of the voltage on the live wire circuit of an electric fence that is powered by a single security energiser. Here the fence end voltage is monitored and if the fence is cut or shorted, the monitored fence will trigger an alarm. This system is generally used around domestic properties where fence lines are fairly short and alarm conditions are easy to react to.

Although the most expensive method of monitoring on a large estate, a high-voltage networked energiser system, in my opinion, is still the best system if zones are kept short (100 m). The systems on shorter distances are not affected by resistance. So, stainless steel wire can be used which is the strongest and longest lasting wire for electric fencing and the only thin wire compound that should be used in coastal regions.

From the guard house every zone has an individually powered energiser that can be switched on and off and controlled via the network-monitored PC system. A fault on one zone will have no effect on another. The closer the energiser kiosks are to each other, the shorter the zones and the more accurately response can react. The introduction of two-zone energisers has helped lower the cost of this system slightly, but a network that can be created via Wi-Fi or fibre is still required.

Low- and high-voltage integration

The cost of multiple energiser stations, the challenges of positioning them in estates and access to electricity caused manufacturers to consider alternate options. Low-voltage integration within a high-voltage circuit allows the installer to extend the high-voltage zones further (say 400 m) and internally partition this larger zone into four 100 m low-voltage zones. This is achieved through hard wiring the low-voltage series zones inside the larger high-voltage zone using a multi-core cable.

Wire resistance is a bit more of an issue here as high-voltage zones are often a bit longer, but stainless-steel wire can still be used. This method saves on field kiosks, but I believe is still almost as secure as an energiser per zone. There is no chance of sector drift as it is hard wired and if a maintenance crew needs to work on the fence, the high voltage can be switched off and the garden crew can trim the fence line while the low-voltage continues to monitor the fence, giving 24/7 total perimeter protection. The multi-core cable needs to be protected from the outside as cutting this will cause a multi-LV alarm, though this will still be limited to the maximum length of that high-voltage zone.

The third and cheapest method and hence a popular method of sectorising a zone is to monitor the current flow (Amps) in the fence and identify a ‘leak’ in a sector of the fence. This method, while having the advantage of being capable of sectorising the fence into multiple sectors and of pinpointing accurately a problem sector, does, however, have a major drawback, namely, that after an initial breach, the system cannot accurately pinpoint any further breaches.

The system is reliant on the high-voltage to create the amperage. (No high-voltage, no detection.) Secondly, focusing only on cost, contractors and security consultants recommend the use of aluminium wire due to its low resistance properties and push the high-voltage zone length to extreme distances. Personally, I don’t like seeing a high-voltage zone being further than 400 m in residential estates, yet these systems are being used on fence lengths of up to two kilometres.

Criminals who have cottoned on to this weakness now cut the fence in one location, wait for armed response to react and then enter through a second, or even third, breach at a distant location. Effectively, the whole fence is down after it has been cut in one place or shorted in two. As the system is amperage monitored after one short, the effectiveness of the monitoring is halved and further shorts or cuts will either not be picked up, or worse, confuse the system and alarm incorrect zones.

These systems are prone to zone drift, especially under fault conditions. I have witnessed the guard room on estates switching the complete system off during an incident as the system continues to alarm multiple zones and create confusion. This means that the perpetrator can now climb out of the estate anywhere without being detected and also with no chance of any shock.

Selecting a solution

Estate managers need to be aware that when an electric fencing manufacturer has only one or two of the above system methods available to zone/sectorise an estate, they will naturally recommend only their system. At JVA/Stafix we have solutions to all three of the monitoring types and as a result I feel can be open about the strengths and weaknesses of each system and recommend a system to match the customers’ individual circumstances.

In our own company’s security outlets and factory complexes, as distances are fairly short (100 - 400 m), we use the high-voltage amperage combination or high-voltage/low-voltage as it is cost-effective with only one energiser system kiosk/point making installation cheap and management easy.

The boundary is short enough to ensure that the response team is quick and perpetrators don’t have the ability or time to create false access points.

In the housing estate where I live, we have energisers in the field with high-voltage monitored zones. Each zone is between 80 m and 120 m. The boundary is a few kilometres in length and we have over 600 houses in an area of around 64 hectares. This means that if one zone is cut, it is identified, but the rest of the boundary continues to function as normal.

The 120 m zone can be further divided by using low-voltage should we require zones of 30 m which would be a definite improvement. However, I would under no circumstances remove the high-voltage zones for the single, long distance, high-voltage zone divided into multiple amperage identified sectors (ZM20 over long distances). I have seen the issues and complications this system has when under intensive interrogation, like happening in Fourways at the moment and do not believe the cost benefits are worth the risk to residents’ personal security.

So, caveat emptor– buyer beware of a salesperson who demonstrates the effectiveness of an amperage sectorisation system by simply walking along the fence and shorting it singly at different locations. It will work perfectly with one short, but apply more than one short at the same time or physically cut a wire in the system and you may find the solution is far from as effective as the consultant may have made it out to be. I have seen many prestigious estates move from reliable systems to new, less effective systems believing the promise of multiple zones and pinpoint detection.

So, what is the answer to this challenge? Personal experience has proved to me that using multiple networked monitored energisers – one per zone at minimum possible distances - is the best, safest and surest way of monitoring sophisticated perimeter systems for large estates to ensure maximum security.

A further improvement to multi-networked monitoring is to divide each zone into sectors using a low-voltage monitor such as the JVA ZLM4 system or even a ZM20, as long as the high-voltage zone it is based on is short enough to be easily manageable. Regrettably, this solution is also generally the costliest, but it is definitely the best. “If you pay peanuts, you get monkeys”, or in this case, unwelcome intruders.

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