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... Read More

What is a Stair Pressurization Fan (SPF)? -- In case of fire in a high rise building, an SPF uses clean outside air to pressurize the air in stairwells. The pressurized air helps people escape... Read More

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? Read More

How Are Fire Alarm Loops Supervised to Make Sure They Continue to Work? -- Because the fire alarm system is a Life Safety System (people's lives depend on the fire alarm system working in an emergency), using supervision, the panel makes sure the field devices are always... Read More

What Makes the End of Line Resistor So Important? -- To allow the panel's internal ohmmeter to check the continuity of the wires (supervise the wires), the end-of-line resistor is at the end of the loop: the last device.Read More

Just What Is a Signaling Line Circuit (SLC)? -- The SLC (Signaling Line Circuit) is another way of saying Data and Power Circuit. Along with added power to run the sub-computers and their input and output circuits, it's a computer data-buss ... Read More

What Is a Conventional Notification Appliance Circuit or NAC?-- NAC is the acronym for Notification Appliance Circuit. Notification: Tells people of a Fire or other Life... Read More

How Does Class A Fire Alarm Wiring Work?-- Fire alarm systems save lives and protect property. Fire alarm systems also break down because... Read More

What is the Difference Between an End of Line Resistor and a Terminating Resistor? -- In electronics, at the end of the communication line, there's often a Terminating Resistor. In fire alarm and security systems ... Read More

What is an RTU (Roof Top Unit)? -- "Help! I have an alarm on my fire alarm panel saying something about RTU, but it won't reset," so goes the cry... Read More

How Does the Panel Know the Address? -- When a fire alarm system is first set up, there are two types of devices that are programmed - one type of device is the Control Panel and the other type of device are all the smoked detectors, heat detectors, pull stations, flow switches, relay outputs, etc...Read More

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...Read More

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?...Read More

Why is There an EOL Resistor on a Pressure Switch? -- In a fire alarm system, all devices have to be continually checked to make sure they never come loose. For conventional devices on Class B systems, like the pressure switch, the best the fire alarm panel can do is make sure the wires are always connected. The resistor is used to make sure...Read More

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...Read More

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...Read More

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...Read More

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...Read More

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...Read More

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... Read More

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-...Read More

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...Read More

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...Read More

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...Read More

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...Read More

Are Addressable Fire Alarm Systems Different from Conventional Systems? -- Many fire alarm people think that an addressable fire alarm system is totally different from a conventional fire alarm system. But is it? A NAC circuit -Notification Appliance Circuit-, for instance, is a totally conventional circuit. Any addressable panel that has a NAC circuit has a conventional NAC circuit. If there are..Read More

What is Voltage Free Interfacing? -- The terms -Potential Free- or -Voltage Free- are engineering terms for -The module has relay contact outputs only-, and it doesn't provide power for anything, or supervise anything -- it doesn't check continuity of any wires. It also doesn't provide power or voltage to activate anything...Read More

What Happens to the SLC when a Device is Disconnected? -- A Signaling Line Circuit (SLC) has two purposes: (1. An SLC is used to send signals between the control panel and the devices on the loop (2. An SLC is used to provide power from the control panel to the devices on the loop. To understand what is going on electrically...Read More

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...Read More

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...Read More

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 ...Read More

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...Read More

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...Read More

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 ...Read More

How is a Pathway Classified? -- The classification for a pathway is not determined by the method of carrying a signal or the type of signal the pathway is carrying - The classification is determined by what the pathway isn't or can't do - the classification is a process of elimination...Read More

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...Read More

Is an EOL Resistor Needed for an Addressable System? -- Normally, as I know, an addressable fire alarm circuit is without end of line resistor and conventional fire alarm circuit has an end of line resistor... But I found some documents online showing the FAS (Fire Alarm System) to work using an end of line resistor to measure electrical current and resistor. So how does an addressable system work? Read More

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... Read More

The Signaling Line Circuit (SLC) is a Data-Power Bus -- The SLC isn't an RS232 communication circuit. The SLC isn't an RS485 communication circuit. Proprietary to each manufacturer, the SLC is its own type of communication-line/power-supply circuit.... Read More

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... Read More

Why is Supervised Wiring So Important? -- Based on Life Safety considerations, supervision makes the difference between building low voltage wiring and building fire alarm system wiring... Read More

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... Read More

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 ... Read More

Is the Fire Alarm Control Panel Necessary? -- Having detected a fire, a fire alarm system sounds the alarm. Other than the building wires that carry the signal from the fire detector to the fire horn, everything else in a fire alarm system ... Read More

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... Read More

How Does Multiplexing of the Signaling Line Circuit Work? -- Depending on what one needs to understand about a circuit, the circuit can be thought about in different ways. Take for instance a Signaling Line Circuit (SLC). A Signaling Line Circuit is a circuit that starts from the... Read More

What Makes the End of Line Resistor So Important? -- To allow the panel's internal ohmmeter to check the continuity of the wires (supervise the wires), the end-of-line resistor is at the end of the loop: the last device.Read More

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 ... Read More

Just What Is a Signaling Line Circuit (SLC)? -- The SLC (Signaling Line Circuit) is another way of saying Data and Power Circuit. Along with added power to run the sub-computers and their input and output circuits, it's a computer data-buss ... Read More

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 ... Read More

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 ... Read More

Why Can't You Reset a Trouble on a Fire Alarm Panel? -- Often times, when going on a service call as a troubleshooter, the building manager or maintenance person says... Read More

Why Have Wire that Lasts 2 Hours in a Fire? -- The fire alarm system is used to tell people when it's their turn to evacuate a burning building. Evacuation sometimes takes time... Read More

What is a Fire Alarm System? -- Long ago, as earliest method of spreading the word of fire danger, people shouted "Fire!" Depending on the circumstances, people would run... Read More

What are those Lights and Buttons on the Fire Alarm System For? -- You're now in charge of the building, be it an apartment building, office building, business complex, or industrial complex and now you have to deal... Read More

What Should One Look For in a Fire Alarm Panel? -- The question has been asked, "Which is the best fire alarm panel?" A fire alarm system isn't: installed for the manufacturer or... Read More

What is Total, Staged, and Defend-in-Place Evacuation? -- For their own safety, when the fire alarm sounds, people want to get out of a burning building. Sometimes, though, there's a hitch ... Read More

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... Read More

Why Have a Written Fire Evacuation Plan? -- One time, I had a fire inspector tell me that he requires a written evacuation plan for all buildings. The reason... Read More

How good are those Call 911 signs above pull stations? -- The Fire Marshal didn't have the authority to require the owner to upgrade the fire alarm system to use off-site monitoring. Because... Read More

I Can't Fix Fire Alarm Systems that are Reset -- Help! I service fire alarm systems. When I'm on call, I have to respond on a 24/7 basis to fix fire alarm systems . This includes those systems that... Read More

Can One Company Really Keep the Other Company In Line? -- I'd like to tell you a story about dishonesty. Not the kind where a vendor knows he is doing wrong, and... Read More

What is Mass Notification? -- When a disaster or emergency strikes, and everyone in the area is to take action now, a Mass Notification... Read More

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 ... Read More

How is a Buffer Relay Wired Into a Door Holder Circuit? -- Like a door stop, a door holder keeps a fire door open. When smoke is detected, the door holder releases, allowing the door to shut. The door holder looks simple and innocuous enough... Read More

How Are Fire Alarm Loops Supervised to Make Sure They Continue to Work? -- Because the fire alarm system is a Life Safety System (people's lives depend on the fire alarm system working in an emergency), using supervision, the panel makes sure the field devices are always... Read More

Why Does the Fire Alarm Panel Supervise the Wires? -- Supervision of building wiring isn't really to make sure the wires are good, supervision of building wiring is to make sure all the devices are ... Read More

How Do You Troubleshoot Using Supervision Voltage? -- With Fire Alarm Systems , one method of troubleshooting is measuring supervision voltage . It's the voltage at the panel's IDC input terminals (Initiating Device Circuit for... Read More

How Does the Fire Panel Know Addressable Detectors are OK? -- It's assumed that fire alarm systems have to work all the time because fires happen anytime, but, then again, this is the real world. Problems with... Read More

What is Fire Alarm Class B Wiring? -- Fire alarm people are paranoid. They're afraid everything is working against them. They're in fear that that if anything goes wrong... Read More

How Does Class A Fire Alarm Wiring Work?-- Fire alarm systems save lives and protect property. Fire alarm systems also break down because... Read More

How is an End of Line Resistor a Pull-Down Resistor? -- Sometimes when troubleshooting, the technician has to think inside the box. For instance, take... Read More

Why Use Class A to Network Fire Alarm Panels Together? -- In a tall building, should the network connecting the fire alarm panels together be Class B, or Class A? Read More

How Does Resistance Affect the Initiating Device Circuit (IDC)? -- IDC circuits (Initiating Device Circuits) are input circuits to the fire alarm control panel, and...Read More

What is a Booster Power Supply or Signal Power Expander? -- A fire alarm system consists of input devices to detect a fire (automatic detectors and manual pull stations), output devices to notify occupants of... Read More

What Is a Conventional Notification Appliance Circuit or NAC?-- NAC is the acronym for Notification Appliance Circuit. Notification: Tells people of a Fire or other Life... Read More

What is Notification Appliance Circuit (NAC) Supervision? -- In the Notification Appliance Circuit (NAC), conventional fire horns, bells, strobes, chimes, and speakers, all have the... Read More

What will a Shorted Fire Strobe Do? -- Some time ago, at a high rise business and condominium building, I inspected a fire alarm system. On arrival, the fire alarm control panel showed...Read More

Why is the Voltage on the Notification Appliance Circuit (NAC) so Weird? -- Normally, when the Notification Appliance Circuit (NAC) isn't in trouble, the NAC is in one of two states or conditions: Alarm (making noise and... Read More

Why does Fire Alarm Strobe Current Go Up as Voltage Goes Down? -- In a fire alarm system, strobes are notification appliances; the flashing strobes get people's attention. They're constant... Read More

What is a Fire Alarm Klaxon? -- Before there were DC fire horns, and as an alternative to clanging bells, klaxons were used to notify... Read More

Why Can't a 70 Volt Speaker be Used With a Fire Alarm System? -- When the fire alarm system is active and is being used for EVAC or voice, there is no difference between the speaker audio used... Read More

What is an RTU (Roof Top Unit)? -- "Help! I have an alarm on my fire alarm panel saying something about RTU, but it won't reset," so goes the cry... Read More

What is Smoke Power on a Fire Alarm Panel? -- 2 Wire Smoke Detectors are connected to the Zone Inputs of a conventional Fire Alarm Control Panel (FACP) , and so too are 4 Wire... Read More

Conventional Four Wire Air Duct Smoke Detectors -- Conventional Air Duct Smoke Detectors are assemblies that include a smoke detector, support electronics, and an internal power supply. The minimum requirements... Read More

What is Smoke Detector Verification?-- Because smoke comes in so many varieties, smoke detectors have to be sensitive... Read More

Should the Detector be Photo, Ion, or Both? -- In a smoke alarm, the smoke detector senses particles in the air from a fire and then the alarm sounds. Hearing the... Read More

Why do Fire Alarm Pull Stations Break? -- Ever wonder why a manual pull station tends to break when someone attempts to push it back after setting off the alarms ? I, too, have been wondering... Read More

Why Does a Smoke Detector Stop the Elevator? -- Back in the early '70s, the disaster movie "Towering Inferno" depicted a fire in a high rise office building. Trapping partygoers... Read More

What is a Firefighter's Telephone System? -- In a large building, so they can talk to each other while battling fires, firefighters use their two-way radios. But when the radios just don't work, the firefighter's... Read More

What is a Stair Pressurization Fan (SPF)? -- In case of fire in a high rise building, an SPF uses clean outside air to pressurize the air in stairwells. The pressurized air helps people escape... Read More

Is the NFPA Code the Law or a Recommendation? -- In the United States, the National Fire Prevention Association (NFPA) fire codes are strange. They aren't codes; they're... Read More