Is There a Detailed Description of the SLC? -- A Signaling Line Circuit (SLC) is more of a concept than a specific wiring method / power source / signal protocol. Each manufacturer uses different methods for their circuits. Some manufacturers have used...
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How is Class B Converted to Class A? -- To be used for controlling a Class A building circuit, the control panel requires separate Class B Output terminals and Class A Input terminals. The exact labeling may be different for each manufacturer, but for an input zone, there has to be 4 screw terminals -- for a NAC output zone, there has to be 4 screw terminals -- for each SLC, there has to be 4 terminals...
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How are the IDC, the NAC, and the SLC Supervised? -- The intent of supervising a fire alarm system was never to just turn on a light and a buzzer - the intent of supervising a fire alarm system is to keep the fire alarm system working to detect fires, and, by sounding the alarm, to warn people. If it wasn't important to always be able to detect fires and warn people, there would be no need for supervision...
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What do I use for a Multiplication Factor? -- I assume from your question that you are calculating the size of needed power backup of the fire alarm system during a 24-hour power blackout, and at the end of 24 hours, either 5 minutes or 15 minutes of sounding the alarm...
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How are Addressable Speaker NACs Supervised? -- One method to supervise the wiring is to use an -end of line device-. There has to be constant or regular intermittent audio sent down the line in order to sense that audio is getting to the end of the line. If not, a trouble is sent to the panel. Another method to supervise the wiring is to put this same end of line device...
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Is it Amplifier Currents and not Speaker Currents for Battery Calcs? -- The quick answer is yes, the amplifier, and not the speakers, would be part of the battery calculations. The problem with audio devices is that, unless the measurements are based on calibrated audio sources, and laboratory equipment is being used, audio voltages and current are impossible to measure accurately. Rather than looking at the speaker's electrical current use, the best that can be done is to base the amplifier's maximum standby current and alarm current on the actual use, under full load and full sound condition...
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What is an Area of Refuge? -- You hear the message "Use the Stairs, "you see the sign "In case of fire, don't take the elevator." To get out of the building from the higher floors, when the building is on fire, the stairs ...
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What Makes a False Alarm so Dangerous? -- Each false fire alarm increases the severity of a real fire. The increased severity from false alarms comes from the greater chance of loss of life or a greater chance of injury. This is a progression - with no false...
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How does Audio Supervision Work on a NAC? -- Speakers, like almost any other device on a conventional fire alarm system, are not supervised; only the wires going to and from the speakers are being supervised. If something goes wrong with a speaker, a horn, a strobe, a pull station, smoke detector, a waterflow switch, or any other conventional device, a trouble will not show up on the panel. No one will know that there's even a problem. The devices have to be actually tested by humans; during a fire when the device doesn't work isn't the time to figure out the device should have been replaced.While the wires are being supervised by the panel, the reason why the devices are not supervised is to...
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Can I use Conventional Detectors on Addressable Systems? -- The NFPA is not against mixing conventional devices and addressable devices, so long as the mixing is in the prescribed acceptance process. The prescribed acceptance process is a procedure using a series of steps for manufacturing, testing, listing for use, labeling, and finally acceptance. Having gone through the steps, the manufacturer shows you in their installation sheets how to connect the parts into the system...
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How do I Address the Pull Stations? -- The numbers that you dial into the devices are address numbers. They're shortcut addresses. Instead of saying -Pull Station, 2nd Floor, North Stair- you dial in the 2 digit number. It's much easier for the electronics to use a 2 digit number instead of the long description; the short number takes a lot less time to send than the long description...
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What do Alarm Output Modules do on the SLC? -- The Signaling Line Circuit -SLC- for the building wiring for a fire alarm system is the communication and power circuit that is connected between the fire alarm panel and the Addressable Input Modules -AIM- and devices, and the Addressable Output Modules -AOM-...
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Can Fire Alarm Software Automatically Assign Addresses? -- With the manufacturer I'm most used to, they can automatically assign the devices to addresses, and the leave it up to the programmer to label the devices. I have found problems with this automatic addressing by fire alarm control panels. The issues that occur become much greater as the fire alarm system becomes larger than the very smallest ones. The issue is in the assigning of location labels. Because each...
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How is the Standby Power Calculated? -- In case there's a power outage, the fire alarm system still has to detect fire and warn people of fire. It would be nice if the fire alarm system could do this for days, weeks, or even years, until eventually the power can be restored, but the NFPA (National Fire Protection Association) is reasonable. In most cases, the NFPA is happy if the system can continue to work without power for 24 hours. This is the standby period. If there is a fire detected at the end of that 24 hours, the system still has to sound the alarm. Usually sounding the alarm takes up a much higher level of current than when the alarm system is standing by, so sounding the alarm has to be calculated separately. This is...
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Can the Input and Output Wires on a Speaker be Reversed? -- Should there be a power blackout, the calculations are designed to show what size of battery is needed to supply enough energy -in the form of electrical current- to make sure the fire alarm system able to detect fire and, once a fire is detected, warn people of the danger...
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Is it Even Legal to Show a Trouble for a Closed Valve? -- What was common to all of the really old panels was that they were three-condition systems. They were either green-light normal, amber-light trouble, or they were in a red-light fire alarm condition. They did not have the relays or the circuitry to be capable of having a dual-alarm system: in addition to the red-light general alarm, they did have an amber-light supervisory alarm...
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Are Breaker Locks Required if There's No Control Panel? -- A Fire Detection and Alarm System is a system that detects fire and warns people of danger. As such, it should never be turned off; it's a life-safety system. If it's 120-volt detectors and pull stations connected to relays that sound bells throughout a building, it's still a life-safety fire alarm system. If it ever was turned off, people occupying a building would not be warned of a fire...
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Can Class A the Feed and Return be in the Same Conduit? -- One way of thinking about a Class A circuit or pathway is to consider that a Circuit is a Circle. The Class A pathway, like a pair of wires, starts out at the panel on the Class B output, goes to the first horn or strobe, to the next, and the next, and finally back to the panel. It then connects to the Class A input. This is a complete circle...
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What are Some of the Technical Issues for CO Detectors? -- An issue with carbon monoxide detectors is they have an Expiration Date. It's not the date that is etched in the law, it's the date that it just won't work anymore. Usually, when the carbon monoxide detector has reached the time it won't work anymore, it will somehow indicate trouble...
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Are We Required to Use Conduit for All Fire Alarms? -- Starting out with the NFPA 70 Code, most of the wiring requirements for conduit are with Class III wiring. With Class III wiring, being power limited wiring, it's allowed to be the rules shown in NFPA 70, which is the National Electrical Code, and also in the NFPA 72, which is specifically fire alarm systems...
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What is Required for Different Types of Detector? -- The National Fire Protection Association (NFPA) talks about smoke detectors in terms of the sensitivity of a smoke detector. The smoke detector has to go into alarm if the smoke reaches a certain level of -Obscuration-. Obscuration is how much smoke it takes to block, or obscure, enough light to...
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Can You Put Initiating Devices on a NAC Panel? -- The letters -NAC- don't stand for the panel-on-the-wall, the letters -NAC- actually stand for the electrical circuit that's outside of the panel. The Notification Appliance Circuit, or NAC is the electrical -Circuit- that carries power to the Notification Appliances like horns and strobes...
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What is the Difference Between Class A and Class B NAC Circuits? -- The short explanation is that coming into the panel for Class A, there are a total of 4 wires, and for Class B, there are a total of 2 wires. However, to understand that short explanation, one needs to know the difference between Class B and Class A from a life-safety point of view. Electricity has to get to the horns and strobes in order for the horns and strobes to warn people of a fire. For electricity to flow, however, the electrons require a complete electrical path. Electrons cannot flow through a wire, unless there is somewhere to go...
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Do We Need an EOL Resistor on a Beam Detector? -- Usually, the Beam Detector comes as a conventional device, meaning that it uses relay contact closures to send a trouble and to send an alarm. When it is not in trouble or alarm, the connections for both the trouble and alarm relays are made to their common and open contacts on the beam detector. That way, if there is trouble...
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What is the Best Way to Test Duct Detectors? -- To find out what happens when a magnet or key is used on a smoke detector or a duct smoke detector, use a magnet or a key. Fires do not carry magnets or keys around with them, so to find out if a duct smoke detector senses smoke, test using canned smoke...
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How are the Horns and Strobes Activated? -- A fire alarm system is a Detect Fire and Warm People about the Fire system. It has automatic detection devices like smoke detectors, heat detectors, and waterflow switches -- it has manually operated input devices like pull stations and MCPs -Manual Call Points-. The detection devices send their alarms to a Fire Alarm Control Panel or FACP. Automatically deciding what to do when there are alarms, the control the control panel has circuitry to sound the alarm. Providing electrical power to...
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How do You Program Fire Alarm Systems? -- To start with, all models of fire alarm system are programmed differently. I don't know of a single source of information that will cover all of them. Mostly the programming manuals for each model has to be consulted. The software is usually user friendly and self-explanatory...
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Are Speaker Circuits Required to be Classified? -- Classification isn't really the exact method of installing wires, classification is knowing how the system deals with failures. When something goes wrong with the system, does the fire alarm system warn the building owner that there's a problem? Is there a method to get around the problem so the system will detect-and-warn even if there's a problem?...
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How is a Ground Fault Different from a Pull Station? -- When the fire alarm system is green light normal, there are no alarms and all wires from the panel to the devices are complete. At this time, the panel is checking continuity of the wires to make sure all devices are connected. It's supervising the wires. The panel is causing a small amount of current to flow out of the panel on one of the screw terminals of the circuit, pushing this current all the way to...
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How Does a Fire Alarm System Work? -- The basic fire alarm system is if a smoke detector goes into alarm, if a pull station is activated, if a waterflow switch is activated, the horns and strobes warn people to take action. Sometimes, other automatic measures...
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How does an SLC Module get Power to Send Signals? -- The power being referred to as being interrupted is generated by the SLC power supply. This is a low current power supply and its output is designed to be regularly shorted out. The panel, though, is looking at the SLC terminals. A lot of the signal sending and receiving is dependent on what the panel is seeing. To see the signals, the Signaling Line Circuit terminals are constantly...
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Can the Fire Alarm Zones be for Multiple Floors? -- A zone on a fire alarm panel display is shown either with labeled lights -like "Basement", "1st Floor", "2nd Floor", "3rd Floor", Etc.- or with words on a graphic display. -- A zone is where you are going to send the fire department when there's a fire -- A zone is where you are going to send the building owners when there's a false alarm -- A zone is where you are going to send the fire alarm technician when the system needs fixing -- If the fire alarm system is an addressable system that uses words on the display, all the devices are shown as separate devices, each device is actually ...
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How Do I Find this Intermittent Ground Fault?-- The ground fault may be there all the time, just not bad enough to always turn on the ground fault light. Sometimes the ground fault is worse, turning on the ground fault light- sometimes the ground fault is better, turning off the ground fault light. Check with technical support for the panel to find out what this threshold for...
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Should the HVAC System be Shut Down on Alarm? -- The idea behind the fire alarm system shutting down the HAVC in case of fire is that the fire alarm shutting-down the fans will save lives. When a fire is detected, rather than allowing the whole building to fill smoke, the fire alarm system closes the fire doors, closes the fire dampers in the ductwork, and shuts down the air circulating fans...
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What do We Include in Battery Calculations? -- When deciding what to include in the battery calculations, we look at the reasons for making these calculations in the first place. A fire alarm system is a life safety system; if the system doesn't work, people can get hurt - or worse. The times that the fire alarm system is supposed to work are -Always-, including the time during a power outage...
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What is the Interfacing Equipment in a Fire Alarm System? -- Much of the interface equipment is installed by others, like the elevators, the sprinkler system, the kitchen's range hood suppression and gas shunt, the HVAC air handlers and smoke dampers, etc. It isn't directly installed, maintained, or serviced by the fire alarm company, but the bottom line is that someone has to take some responsibility for the entire Fire Detection and Alarm System...
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How are Lamps Tested on Fire Alarm Panels? -- The purpose of the lamp test is to catch problems with the lamps before there is a fire. In the olden days, before there were LED lamps, there were incandescent lamps. Incandescent lamps used a small wire -the filament- that got hot enough to produce light. It may take many years, but eventually all incandescent lamps burn out; their filaments burn out. Some will burn out sooner than others...
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Do I Have to Use a PVC Pipe That's Listed? -- The NFPA 72 Code in their definitions say that an Air Sampling-Type Detector consists of the pipe or tubing network connected to the detector where the air is then analyzed. That means that in order to be listed as an air sampling-type smoke detector, the manufacturer's PVC pipe is listed to be used with the specific air sampling system...
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What is the Maximum Number of Zones Permitted? -- The NFPA (National Fire Protection Association) doesn't decide how many inputs or outputs can be on a fire alarm panel, and they don't decide how many zones we can attach to a fire alarm control panel. These decisions are left up to the manufacturer of the panel. The NFPA, however, does indirectly control how well the panel is going to work. Once the panel is designed and ready, the manufacturer has to get the panel tested by a...
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Can the Fire Alarm Control Panel Trip a Remote NAC Panel? -- The panel's output to the NAC Circuit (Notification Appliance Circuit) has two conditions. When the panel is not in alarm, the panel is supervising the wiring in the circuit by checking the continuity of the Conventional Class A or Class B wires. A small current is run through one of the wires, the end of line resistor, and back through the other wire. If the current stops because the wire breaks or comes loose, the panel's trouble light and buzzer are turned on...
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Is it Mandatory to use 20.4 Volts for NAC Calculations? -- To understand the requirements in the code, the question isn't -Is it mandatory to follow the code?-, the question is -Why?-. To understand the -Why- of the requirements, we have to backwards-engineer the requirements. When performing the voltage drop calculations for the Notification Appliance Circuit (NAC), there are two concerns that have to be dealt with before even determining what voltage to use. One is Life-Safety and Reasonableness, and the other is...
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Can There be Too Many T-Taps on an SLC? -- As a technician trying to follow wires through a building, trying to fix a problem with the wiring can be made more difficult because of the number of T-Taps. If there aren't enough T-taps, sometimes trying to follow the wire past all of the devices...
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What Happens when One Battery is Hooked In Backwards? -- Sealed Lead Acid batteries have very little internal resistance, so a forward 12-volt battery and a reversed 12-volt battery connected in series constitute a dead short. This, though, is when they are first connected to a charger. If there's an internal fuse on the charger, the fuse will probably burn out. If there isn't a fuse, probably the charger has some sort of current limiting. This part is mostly a design issue for the charger circuit, and the design will be different for each model of Fire Alarm Control Panel or NAC Power Supply...
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What Causes an Open NAC? -- I am going to a job site where on the service call ticket states that a NAC is reading open circuit. What can cause an open circuit on the NAC line?
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How do I Fix this Comm Fail Light? -- Listen to the Phone Lines. The only way to tell what is happening on the telephone lines is to listen to them. Use your butt set as a test tool to hear exactly what is happening. Just listening to what is happening can help you understand what is wrong. The sequence is...
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Does Anyone Make a Generator/Tester for SLC Circuits? -- There are no actual test generators designed for fire alarm system Signaling Line Circuits -SLCs-. The real reason has a root cause in attitude. All manufacturers are extremely proprietary. The attitude is because they are afraid that if anyone can connect another manufacturer's equipment to their Type Accepted Fire Alarm System, and something bad happens...
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Are Smoke Detectors Needed Above False Ceilings? -- Occupancy, and the type of fire alarm system that should be installed, is determined by the NFPA 101 or the International Building Code. These books show that one type of occupancy, for instance a gas or petrol station, requires a totally different type of fire alarm system than an apartment building. The books also indicate that for some types of occupancy, total coverage by smoke detectors is required, and pull stations are required at all exits... except if the building has total coverage by a...
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Can I Use a NAC Circuit for a Sounder Base? -- When the horns and strobes in the hallways of the building are not sounding the alarm -the alarm is silent-, the sounder base circuit is still providing full power to the sounder base. That is so the smoke detector can turn on the sounder base when the rest of the building is silent. Think of the sounder base and the attached smoke detector as a residential smoke alarm...
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Why Doesn't the SPF Turn-On with Smoke in the Stairway? -- There's a problem with smoke in the stairwell. More people die in a fire because they breathed smoke than people die because they were burned. Because of that, so that people can escape both fire and smoke, they use the narrow stairwell as an escape route. The stairwell has to be free of smoke...
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What is the Trigger Voltage for a Booster Power Supply? -- Most fire alarm control panels can provide a limited amount of power for the horns and strobes, but extra power for the horns and strobes can be provided by a Booster Power Supply -BPS-. The term -Trigger Voltage- for the BPS is a shorthand term for -Whatever voltage is necessary to turn on the Booster Power Supply-. Depending on...
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Can There be More than One EOL Resistor? -- From an electrical point of view, there is a problem with adding extra End of Line Resistors. From a life-safety point of view, there is a problem with more than one End of Line Resistor. From a legal point of view, there is a problem with installing the system differently than what is shown in the installation manual...
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Do I Have to Use a PVC Pipe That's Listed? -- The word Listed means that a nationally known, third-party testing laboratory like UL, ULC, CE, FM, etc. has tested the pipe for use in Aspiration Systems for Air Sampling. Once the testing laboratory knows that the pipe is going to be adequate for this purpose, they say that it is adequate by...
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What is a Repeater Panel in a Fire Alarm System? -- A Repeater panel is used in a remote location, away from the control panel. It passively displays the condition of the fire alarm panel. If there are control buttons on the Repeater panel, it can also actively control the fire alarm system. A LCD display is an expanded version of the Repeater panel...
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What is a Fire Alarm System? -- The idea behind fire alarm systems is to save lives and protect property. A fire alarm system does this by detecting fire -either automatically or when someone sees a fire- and then warning everyone in the building about the fire. A person, having seen a fire, could run down the halls shouting...
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When Should I use Shielded Cable in a Fire Alarm System? -- All fire alarm systems are package-deals. They are all fire alarm systems tested and certified as being reliable by third-party testing laboratories like UL, FM, ULC, CE, CCC, etc. This testing included the type of wire being used between the control panel and the devices...
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Where Should I Install the Fire Control Panel? -- If all the horns and strobes in the entire building sound off so everyone in the building leaves in less than five minutes, then any fire protection of the fire alarm system only has to be good enough for everyone to leave. If only some of the people are told to leave, and some people wait their turn to leave, then once a fire starts, any fire alarm equipment including...
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How Important is it to Label Wires? -- Good options for the labels come in two varieties --- Labeling Machines - The labels look good, but care must be taken in choosing the machine type. --- Cloth Tape - The labels looks ugly, and care must be taken in choosing the tape type. However, the writing put on the tape using sharpie pens NEVER rubs off...
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What is a 4 Wire Smoke Detector? -- Even though it uses an internal protection resistor and internal alarm relay contacts, a 4 wire smoke detector is basically a 2 wire smoke detector; it detects smoke and sends an alarm ...
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Why Doesn't a Smoke Detector Always Detect? -- The NFPA wants smoke detectors tested in place to make sure smoke enters the smoke chamber. Keep in mind that a smoke detector can't detect smoke that doesn't get to the detector. When a smoke detector doesn't...
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What's the Difference Between Class A and Class B? -- The Fire Alarm System is a Life Safety System - so the occupants of a building can escape quickly, the idea behind a Fire Alarm System is that it will provide a warning that there is a fire. The trouble is, if something is wrong with the system, like a wire is broken somewhere in the building, the Fire Alarm System...
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What Is the Difference Between Conventional and Addressable? -- The word conventional doesn't mean Old and Obsolete, the word conventional means Sanctioned by General Custom. The conventional fire alarm system is the standard way, or ordinary way of making a fire alarm system. The Addressable portion of a fire alarm system isn't a replacement for a conventional fire alarm system, the Addressable portion is ...
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Firefighter Don't Reset the False Alarm -- When the alarm sounds and the firefighter arrives, even for a false alarm, the firefighter is on site for property protection and life safety. So when leaving, from the point of view of the firefighter, the ...
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NFPA's 7 Classes of Fire Alarm Paths -- The NFPA has divided the signal paths in a fire alarm system into 7 classifications: Class A, Class B, Class C, Class D, Class E, Class N, Class X. These classifications don't show how to wire up anything, these classifications show what happens when things go wrong...
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If It's There -- It Has To Work -- Whether its smoke detectors on the ceiling or the firefighter's telephone system, people think that if it's there, it's real and it works. Sometimes, people even stake their lives on that device or system ...
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What is Class N Power Over Internet (PoE)? -- Powering detectors and modules, Class N communication paths using Power over Ethernet (PoE) is coming to a fire alarm system near you. Probably not all of the systems or devices will use Class N PoE paths, but enough...
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What Is Fire Alarm Trouble Power? -- In the "Old School" type of fire alarm system, before the smoke detector was invented, even though the fire alarm systems used AC, all voltages were in a steady state: either on or off. Until someone ...
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What is a Four Wire Smoke Detector? -- A 4-wire smoke detector is just like a 2-wire smoke detector, except that it receives its power from an auxiliary power supply rather than the conventional Initiating Device Circuit. Both the 4-wire and the 2-wire smoke detector sense particles in the air and call the particles smoke...
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What is a Fire Alarm Zone? -- Building zones aren't determined by where the wires are run for the fire alarm system, building zones are determined by the building's fire-control -- fire-fighting divisions and by the building's smoke-control divisions...
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