The National Electric Code distinguishes five major types of fire alarm wires based on the places where they are permitted for operation. These are listed in order of priority, with Type I being the highest priority and therefore used first when installing a fire alarm system.
Wires of Types II-V will operate to transmit an alarm when heated by a fire to designated monitoring stations.
Type I Fire Alarm Wiring: This is the highest priority type of wiring. It must be run to all rooms with smoke detectors, either battery powered or hardwired to the local utility. The cable should be separated from other living areas's circuits and connected to each detector directly. This type of cable can also be run between buildings if both have separate power sources and there are no shared circuits between them. The cable should be separated from other people's circuits as far as possible.
Type II Fire Alarm Wiring: Used for general purpose distribution centers and large rooms that do not have smoke detectors. This type of cable is most often used in commercial buildings and multiunit residential structures. It should be separated from other living areas's circuits as far as possible.
Ionization, photoelectric, and combination alarms are the three basic types of fire alarm monitoring systems. We will go through each sort of alarm and how they can aid in the detection of fires in the sections that follow.
Ionization sensors measure the presence of smoke by detecting the positive ions generated when smoke particles pass through an electrical field. These sensors are generally found in large public buildings where smoke damage is a concern. Ionization sensors do not need to be within sight of the source of the fire to detect it.
Photoelectric sensors work on similar principles as ionization sensors but use light beams instead of electrical fields to detect smoke. They are commonly used in small private dwellings or offices where smoke damage is not a concern. Photoelectric sensors cannot detect the presence of fire until after it has reached operational temperatures, so they require direct visual contact with the flames or hot objects for activation.
Combination sensors combine the features of ionization and photoelectric sensors and are useful in large public buildings or industrial facilities where both ionization- and photoelectric-based systems are installed. They can detect the presence of fire at any temperature and come fully equipped with their own power supply so they can operate even if other parts of the system have failed.
Ionization sensors use electricity to detect smoke; therefore, they must be powered up in order to function.
According to a building inspection firm and my fire alarm installer, the requirements need different types of cable for fire alarm wiring. I'm talking about the connection that connects the sensors/sounders to the control panel in a system to LD2, as specified in BS5839 pt6. They call this type of cable FDOH (fire detection output hookup). Here are the details:
The control panel must be located not more than 150 feet from the first sensor/alarm unit and not less than 30 feet from any other sensor/alarm unit. The control panel must be directly connected to the house wiring which enters the property at a point not more than 20 feet from where it leaves the wall structure. The control panel must be accessible from a hallway or other means of egress. The control panel must be hard-wired to the house wiring.
So, for a system with three sensors, you would need three sets of FDOH cable. One set of cable for the line side, one set of cable for the load side. Each set of cable needs to be capable of conducting current up to 15 milliamps per conductor. So, three sets of cable with six conductors each equals 90 feet of cable. You will also need two terminals (blades) for connecting each set of cable to the control panel. These terminals must be marked L1 and L2 for line 1 and line 2.
Fire and Security: The Five Major Types of Fire Suppression Systems.
Traditional water-based fire protection uses hoses to deliver water directly onto a fire. This method is effective for small fires, but not for large-scale fires or structural fires. Water can also be delivered using the foam produced by a fire engine or sprayer truck. Foam reduces heat exposure to people and property while putting out the fire. Modern appliances use various methods of delivering chemicals into the atmosphere to produce a smoke screen that prevents oxygen from reaching burning material, thus suppressing flames and smoke. These devices include dry chemical agents, such as potassium nitrate, and carbon dioxide gas. Smoke detectors function by sending a signal to a central station when they detect smoke.
Water-based alternatives exist for large-scale fires and structural fires. In traditional fire suppression, engines with high-pressure pumps fight the fire with water from their hydrant sources. The Los Angeles Fire Department, for example, uses 50-60 foot hydrants connected to manholes located in parking lots across the city. These hydrants can supply up to 200 gallons of water per minute during peak hours.
The Four Different Types of Fire Detectors Understanding the distinctions between them is the best way to identify which type is appropriate for your business or property. Ionization/photoelectric, photoelectric, ionization, and heat detectors are the four types of fire detectors. They all work by detecting smoke, heat, flame, and explosion in the presence of oxygen.
Ionization/Photoelectric Fire Detection Systems These systems use ionization sensors that measure the intensity of electric fields within the sensor itself. If smoke enters the field, it changes the amount of charge within the sensor, which can be detected by measuring the voltage across it. Photoelectric systems work similarly, except that they use photodiodes instead of ionization chambers. These sensors are more sensitive than their ionization counterparts, so less smoke is needed to trigger an alert.
Heat Sensors Heat sensors detect elevated temperatures inside a protected space. When smoke enters the sensing area of the detector, it lowers the temperature within the sensor's casing, triggering an alert. Unlike other types of fire detectors, heat sensors do not need power to operate; therefore, they are ideal for use in areas without a permanent power supply such as residential security systems and commercial building alarms.
Smoke Sensors Smoke sensors are designed to detect smoke in air streams. As air flows through the sensor, it triggers an alert if smoke enters the stream.