Intruder Alarm Design Considerations

[Secware_Tech6]

When designing an intruder alarm systems some basic information needs to be gathered. Apart from the specialist regulations (BS 4737 has been withdrawn) of BS EN 50131, PD6662, DD243 etc, BS 7671 and Part P is still relevant for cable sizing, methods of fixing recording voltages etc. But lets start with some basics

 

1, Domestic Installations

 

Probably one of the most common systems. This would usually be a Grade 1 or 2x (both audible only). A risk assessment must be carried out and this will decide grade. Also the insurance company may have some input on a minimum grade they will accept. Look for things like easy access points, flat roofs, weak doors etc. These areas need special attention and may require additional protection such as vibration sensors or door contacts. Consider how you would gain entry yourself, this will highlight potential weak points. But generally a system design will consist of door contacts on the front and possibly rear doors, movement detection in the hallway, lounge, kitchen and landing. The idea of just doing the landing upstairs is any intruder will have to cross the landing when changing rooms. There may be a case for additional protection ie landing window due to flat roof, master bedroom PIR or Panic button, or high tech equipment in a study. Also garages may need some protection.

The keypad is usually fitted in a convenient position in the hallway. Some keypads have on-board PA features, so the keypad should always be accessible if need in an emergency. You should also fit an internal sounder so that exit tones can be heard throughout the exit route, and will also function as an internal sounder. External sounders should be fitted as high as practicable, and the cable should not be visible. You may also consider smoke or gas detection, these are getting more popular along with 'fobs' for ease of use. Once you have a basic design then you can quote the system based on the amount of equipment needed.

As a rough guide a professional install of a grade 2x system with 4 - 5 PIR's should take 2 man days. There are companies that can do it in 1 or even a few hours but to do the install properly you should allow 2 days at your labour rate. Cables should be routed under boards, away from any existing cabling and fixed where necessary. Care should be taken when running a new cable through holes with existing cables (i.e. an upgrade) as pulling the cables through too quickly will burn the existing cables. Once you have all your cables in place from all your points to the control location, you will be ready for the Second Fix.

 

Second Fix

All equipment must be securely fixed. Normally on a plaster wall, wall plugs and screws of the correct size for the weight of the device will be used. The only exception to this is the sounder where you must use screws of a No. 10 in size and must protrude through the back plate at least 2 Inches.

 

Connections

See the manuals for detailed wiring instructions such as tamper series loops, or eol wiring. Most grade 1 and 2x systems will use a 'double pole' topology. i.e. the alarm contacts will be wired in to 1 pair of wires and the tamer will be on a 2nd pair. So there will be 2 'poles' at the detector. EOL wiring usually consists of 2 End Of Line resistors (value depends on manufacturer galaxy 1k and 1k), this allows for the alarm and tamper to be on the same pair and the panel can calculate what is in alarm by measuring the resistance of the circuit. The higher security grade 3 systems utilise anti-mask and an additional resistor is used to monitor the mask detector. PA devices usually only have an alarm pair.

 

Testing

Once your system is fully connected you need to perform various performance tests, ie walk tests etc as detailed in the manual of the control equipment you are fitting. Follow these steps tp check the operational performance. You should also record the system record checks, ie the 'readings'. These consist of the battery charging voltage, disconnect the battery and meter between +ve and -ve the reading obtained should be approx 13.6 - 13.9v. AC input voltage which should be around 220-240v. The voltage at each detector, and the resistance of the cable to each device. Alarm cable should be around 9 Ohms per 100m.

 

Handover

Show the customer how to use the system fully, change any default manager and user codes. Usually you will have your own engineer code that you will program up. While some panels allow you to 'lock' the engineer code to prevent takeover, many engineers consider this bad practice so be sure you understand the implications of you intend to use this feature. Sign the completion paperwork and obviously collect payment.

We would advise your service contact details are clearly marked on the control equipment.

 

2, Commercial Installations

 

 

As with a domestic install but will probably be a higher risk, so additional protection will be required. As most commercial sites have few people to hear an alarm some sort of remote signalling is preferred, be that a voice/speech dialler or monitoring via an alarm receiving centre.