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This chapter is from the book

This chapter is from the book

Location Considerations when Designing a Security or Fire Alarm System

Each component of a home security and surveillance system is designed to be used in a specific location. Window sensors have requirements that are different from door sensor requirements, and smoke and heat detectors each have special location requirements. Computer systems can be integrated with control protocols such as X10 and CEBus to operate and manage security systems. In the following paragraphs, you will discover how smoke detectors work and where they are located. Also covered are the functional design requirements for various types of home security system components.

Home Utility Outlet Specifications

Home security systems require a number of utility outlets to support the installation of sensors, sirens, controllers, surveillance cameras, security lights, and motion detectors throughout the home. New construction provides the opportunity to install structured wiring outlets in all rooms of the home. This includes 120v AC power outlets, Category 5 UTP cable outlets, #22-gauge two-pair wiring for sensors, and RG-6 coaxial cable outlets.

Cohesion with Existing Home Systems

The security system should have sensors located in areas where components of existing home systems require monitoring or protection from theft.

Heat sensors are the most common type of sensor for monitoring components of the heating, ventilation, and air conditioning (HVAC) system. They are mounted near the furnace to monitor rapid changes in temperature that could warn of a possible fire.

Security systems area often designed to be integrated with the home computer system. Computer interfaces are used with X10 and CEBus protocols to monitor and control interior and exterior security system components.

Safety and Code Regulations

The safety and code regulations for installing and locating fire alarms, sensors, and smoke detectors are usually governed by local building codes. The local codes are enforced by a fire marshal who conducts inspections of public places and sets the standard for local residential inspections.

Smoke Detector Installation and Location Requirements

On the national level, codes and standards have been published that establish the requirement for fire detection equipment installation. As an example, a home must have at least one smoke detector installed to meet National Fire Protection Association (NFPA) Rule 72 and Underwriters Laboratories, Inc. (UL) 985 standards. The UL 985 standard covers household fire warning system control units intended to be installed in accordance with the National Fire Alarm Code (ANSI/NFPA 72) and the National Electrical Code (ANSI/NFPA 70).

ANSI/NFPA 72 is the standard document that defines the spacing for smoke detectors, which is typically 30 feet when installed on a smooth ceiling.

Existing Home Environments

Existing home environments require new wire and cabling to support security system components where hard-wired systems are installed. Wireless systems are popular for existing home environments because of the convenience of locating sensors without the need to install additional wiring in the walls.

Smoke Alarm Requirements

Smoke alarm requirements are not the same for every home. They vary according to local municipal standards and the age of a specific dwelling. For homes built prior to 1979, battery-powered smoke alarms are permissible. As to smoke alarm placement, requirements also vary according to the age of the dwelling.

New Home Construction Environments

New home construction facilitates the location of hard-wired security system wiring and components during the early phase of the construction. Structured wiring in new homes supports most of the needs of a well-planned multizone security system. Phone lines, coaxial cable, and Category 5 cable are components of a structured wiring installation. They provide the basis for integrating the security system with the computer network and other home automation systems. The exception is the wiring for door, window, and motion detector sensors. Inexpensive two-conductor wire must be installed in the interiors of walls between the controller location and each sensor. In addition, two-pair #22-gauge wire must be installed for all low-voltage powered sensors such as motion detectors. One pair is used for power and the other pair is used for signaling.

Smoke Alarms in New Home Construction

For all new home construction, fire alarm sensors must be powered by the home AC power electrical wiring. Although this overcomes the problem of neglecting to replace batteries on a periodic basis, there remains the problem of power outages that would also disable a fire warning sensor that uses the home wiring as a power source. Sensors can be purchased with integrated battery powered backups.

For homes built prior to 1979, battery-powered smoke alarms are permissible. In newer dwellings, alarms must be powered by the electrical wiring. The problem with battery units is that people often neglect battery replacement. On the other hand, what good are wired-in smoke alarms if you have an electrical fire accompanied by a power outage? The safest arrangement, therefore, is to install wired-in alarms equipped with battery backup. This type of integrated alarm can be obtained at most hardware stores and is required for homes built as of 1993.

As to smoke alarm placement, requirements also vary according to the age of the dwelling. In older homes, most municipalities require alarms in the following locations: within close proximity to all bedroom entrances, on each story of a multilevel home, and in basements. The latest standards, enacted in 1993, require that there be an additional alarm in each bedroom. Another practical location, although not required, is the garage.

Equipment Functionality and Specifications

Each component of a home security and surveillance system has a specific function to perform. The basic security system includes a control panel connected by cables to sensors at various locations throughout the home. A perimeter protection system must include sensors at every opening, including doors, windows, garage doors and windows, and doors to crawl spaces. A keypad is the device that provides a control interface for the residents to arm and disarm the system using a programmed access code and also to monitor the status of the system.

Door Functional Design Specifications

Doors are protected by installing small magnetic switches inside the frame. Figure 3.1 illustrates the location of the magnetic switch. A magnet is installed in the top of the door that keeps the switch contacts open as long as the door remains closed. An alarm is caused when this switch is disturbed by opening the door. The magnetic switch completes a circuit that is connected to the control panel. Recessed mounted models use magnets that are fitted into drilled holes, and when properly installed, recessed mounted magnetic switches are hard to notice and blend in well with the door.

Figure 3.1Figure 3.1 Magnetic door switch.

Window Functional Design Specifications

A perimeter security system must include a glass protection system because magnetic switches do not protect against an intruder entering through a broken window. Glass protection systems are available in two categories: vibration and acoustical. The vibration system is mounted on the glass or on a nearby wall and detects movement of the glass. Acoustical systems, or sound discriminators, sense the sound of breaking glass. The unit can be tuned to react only to the specific frequency of glass breaking, typically 4KHz–6KHz, or it can react to any loud noise. Some manufacturers have combined vibration and sound detectors into one unit that does not activate unless both are detected. These units can be used where the normal conditions would cause a single technology detector to generate false alarms.

Control Panel Functional Design Specifications

The control panel shown in Figure 3.2 is an enclosure that contains all the electronic components, wire termination points, backup battery packs, and telephone termination wiring.

Figure 3.2Figure 3.2 Control panel.

Each sensor receives power and is managed from the control panel. It monitors the health and operating status of the total system and sends a signal to the siren when an alarm condition exists. The panel should be mounted in a location that is out of plain view and near a 120v AC outlet where a plug-in transformer can be used to supply low-voltage power to the total system. If a phone line is planned for connection to an external monitoring facility, access to the location where the phone line enters the home must be considered when locating the control panel. Preferred locations are utility rooms, basements, and closets.

Keypad Functional Design Specifications

The best location for a keypad is an area that is both convenient to the family users and secure for the system. The homeowner must ultimately determine how many keypads are desired and where they are to be located in the home. Typically, keypads are placed at the main entry/exit door, in the master bedroom, or in the main hallway of the home. In a multilevel home, keypads are commonly placed on each level.

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