Is 2 Hour Rated CI Cable Too Much?

2 hour CI Cable and Survivability

As you may already know, UL (Underwriters Laboratories) has pulled their listing on 2-hour rated circuit integrity (CI) cable.  Since this cable technically no longer exists, what are we to do in current and future installations requiring the use of this CI cable?  According to the UL document, it is now up to the discretion of the local AHJ as to when it can be used or substituted with an alternate means of media.

Now, where did the 2-hour rating come from?  It is my understanding that stairwells are required to be 2-hour rated in buildings over four stories in height.  With buildings that are four stories and under in size, you will typically have a general alarm sequence and won't require any Pathway Survivability.  Buildings over four stories start getting close to the threshold for a high rise building where pathway survivability defiantly plays a role.  Depending on the level of Pathway Survivability (see NFPA 72 2010 section 12.4) level 0, 1, 2, or 3 you will have to protect your circuit pathway for a period of two hours.  Now this can be accomplished by either installing 2-hour rated cable or CI cable, 2-hour rated cable system [electrical circuit protective system(s)], 2-hour rated enclosure or protected area, or 2-hour performance alternatives approved by the authority having jurisdiction (AHJ).  Note that level 0 has no requirement for pathway survivability and level 1 can be accomplished if the building is fully protected by an automatic sprinkler system.

To make it simple, you can run your cables for a fire fighters telephone circuit up a 2-hour rated stairwell without the use of CI cable.  However, when you exit the stairwell to extend the circuit to other areas of the building, you need to use 2-hour rated CI cable.  The intent in my mind is to provide a complete circuit pathway from the fire alarm control unit FACU to the field devices with a rating of not less than 2 hours.

Alright, so the concept is clear, you want to provide a fire alarm system that is capable of lasting at a minimum, 2 hours in the event of a fire.  This allows time for all of the occupants to evacuate and remain clear of the building.  After all it is the ultimate goal of a fire alarm, voice evacuation or mass notification system to notify the occupants of the emergency at hand.  If the wiring fails then obviously you no longer have the ability to broadcast out to your field notification appliances.  Now this is where it gets crazy.  The FACU or Fire Alarm Control Unit is not required to be 2-hour rated nor are the field devices such as fire fighter's telephone jacks, speakers, strobes, horns, etc.  So how is it that we have codes in place to insure that our fire alarm circuit pathways are secure for a period of 2 hours but not the control or notification equipment.  If there is a fire in a high rise that lasts 2 hours, the field devices would not stand a chance.  So what do we have when the fire is all said and done?  A voice evacuation system with operational cables but nothing to activate, control or notify. 

I am not sure as to why UL pulled their listing on CI cable but I honestly am not up in arms about it.  UL is remaining very silent on the issue and will not disclose any information regarding the test results of CI cables.  At this time, to save your customer money and your technicians the hassle  I recommend bringing this topic up with your local AHJ and finding out if he/she will allow the use of other cables in applications requiring NFPA 72 Pathway Survivability Levels 2 or 3.


If you are interested in taking the NICET CBT exam for fire alarms, then we have you covered!  We are now selling our CBT Levels 1 - 3 practice exam DVDs.  These DVDs are packed with tons of NICET CBT practice exams along with all code references as to where to find the answers.  We have also supplied the DVDs with all of the necessary NICET applications, CBT calculator demonstrations, links and more.  If you need more information, feel free to send an email.  You can find the link to purchase our DVDs on the top left section of each page on this site.

Direct Burial Cable for Fire Alarms

Did you know you could direct bury fire alarm cables if codes and standards are followed?

Have you ever used direct burial cable in your fire alarm installations? Typically in fire alarm you will not see much of it as most of our outdoor work is typically in Rigid conduit or schedule 80 PVC.  Also a small portion of our fire alarm designs involve running out side for connections.  Without getting too deep in the design aspects, more than likely, if you are running circuits outside, are likely for a PIV (Post Indicator Valve), or Backflow Preventor with OS&Y switches (OS&Y standards for Outside Screw and Yoke)

Direct burial cable is a cable that is designed and U.L. approved to be installed directly in trenches without the need for conduit or other raceways.  The wires themselves are encased with what is known as a thermoplastic sheath that seals out moisture to help protect the wires. Direct burial cable often referred to as UF Cable and commonly ships with a grey jacket. However, there are some wire manufacturers such as Beach Wire and Cable, Arrow Wire and Cable, and Windy City Wire that make their own listed direct burial cable and it comes in black. Please note that this type of cable is only listed for this use if it is installed at the proper depths.

An easy way to notice the difference between standard non-metallic sheathed cable (NM) and underground feeder cable (UF) is the coating around each cable within the jacket. NM cable is simply a jacket to house multiple conductors whereas the UF cable separately coats each conductor.

Why is Copper So Popular in Electronics

The electron theory is a good way to explain why copper wire is widely used with electronic equipment and in electrical power distribution. Every substance whether in earth or in space is made up of tiny particles called atoms. These atoms are so small that a piece of copper the size of the head of a needle would contain millions of atoms. Each one of these copper atoms could be considered an actual piece of copper. An atom is not a solid piece of material. The atom itself contains a nucleus in the center which has a positive electrical charge. Traveling around the nucleus in elliptical rings are electrons which have a negative electrical charge. Every electron has the same mass and the same negative charge. There will normally be just enough electrons in the atom to balance the positive charge of the nucleus.


In the diagram below, you will notce that each ring can only contain a certain amount of electrons. The first ring can house 2 electrons, the second ring can hold 8 electrons, the third ring can handle 18 electrons and the fourth ring can hold 32 electrons.

The copper atom's nucleus has a positive charge of 29 in the nucleus. There are typically 29 electrons within the copper atom. With that said, the fourth ring will only house one electron.

When the outer ring of electrons in an atom is filled to the maximum amount possible, that atom will be very stable electronically and chemically. It is almost impossible to remove an electron or to force in an electron.  If the outer ring only has one electron in it, than that electron is not held very closely to the atom and can be easily moved out of its position into space or another atom. This will leave the atom short of one electron to neutralize the positive charge of its nucleus. This will leave the atom with a positive charge.

This is the reason copper wire is so widely used in the electronics industry. It is highly conductive due to its makeup.


If you are interested in taking the NICET CBT exam for fire alarms, then we have you covered!  We are now selling our CBT Levels 1 - 3 practice exam DVDs.  These DVDs are packed with tons of NICET CBT practice exams along with all code references as to where to find the answers.  We have also supplied the DVDs with all of the necessary NICET applications, CBT calculator demonstrations, links and more.  If you need more information, feel free to send an email.  You can find the link to purchase our DVDs on the top left section of each page on this site.

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Ground Fault found On PAM Relay Leg

Today I had the pleasure of working on a Saturday. It was a service call to track down and locate a ground fault on a Fire Lite FCPS24 NAC power supply. This ground fault is the reason another company felt it was necessary to disconnect the NAC circuit from the main fire control panel to the NAC circuit power supply. Read about here.

We traced out the ground fault on the negative power wire (constant power used for global HVAC shut down) to the rooftop air conditioning units. Upon a close examination of the unit with the ground fault we found that the 120VAC power leg (black) wire on the PAM-1 relay had been pinched in between the 4 S box and cover.

In this case our fire alarm control panel or FCPS24 NAC power supply was powering up the PAM-1 relays. This mean we connected our constant power to the Red (positive) and White (common) wires on the PAM-1 relay. Therefore the black wire is not used. However, the 120VAC lead (black wire) can still transfer a ground fault through the coil.

Always make sure to cap off the black lead and ensure it is not grounded out when using the PAM-1 relay for HVAC shutdown, elevator recall, door holder, etc.

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New UL Smoke Alarm Requirements in California

I just attended the monthly CAFAA (California Automatic Fire Alarm Association) meeting and was surprised to find out the new requirements set forth by UL for single and multi-station smoke alarms.  Now these are just for the smoke alarms in household applications.  Not to be confused with system smoke detectors (tied to a building fire alarm system).  The State of California has let a crazy requirement slip through and become adopted for these stand alone household smoke alarms to take effect January 1, 2014.  Get this, the smoke alarms are now required to have the following:

1. If the stand alone single station or multi-station smoke alarm is battery operated, the battery has to be sealed in the detector, non-removable, and have a lifetime of 10 years.
2. The smoke alarm has to be monitored for end of life
3. The smoke alarm has to have the manufacture date and installation date clearly visible
4. The smoke alarm must have a Hush feature

Now some manufactures have smoke alarms out there that have some of these features including the Hush feature, 10 year battery and manufacture/installation dates.  Now the tricky one is the monitoring for "End of Life".  The California State Fire Marshall's (CSFM) office reads this as the necessity to provide smoke detectors tied to a building fire alarm system as they can be monitored for dirty sensing elements.  I read it differently.  Manufacturers such as Kidde have detectors with a 10 year battery life.  With that said, the detector will chirp when the battery is at a low level indicating in my mind, "End of Life".  If the detector starts to chirp, it is notifying you that the battery is near dead resulting in the "End of Life" for the smoke alarm detector.

The CSFM has also stated that these requirements are not going to be in affect for wireless battery operated smoke alarms as they report back to a fire alarm system.

Any thoughts on this?

UL Requires Site Specific 2-Wire Smoke Detector Compatability

Word on the street is that UL (Underwriters Laboratories) is stating new requirements for the certification in listing compatibility for 2-wire smoke detectors.  If you or your customers have a an FACP (fire alarm control panel) with 2-wire conventional smoke detectors you may be affected by this.

If you have the need to replace 2-wire smoke detectors on your existing fire alarm control panel and cannot find UL listed detectors, then you need to know this:   UL is toying with the idea of site specific testing for the certification in listing 2-wire smoke detectors.

What does this mean for you or your customers?

Answer:  In the case of an older panel that does not have 2-wire smoke detectors Listed for compatibility, you will have to pay UL to come out to the site and perform their testing.  Now this is not set in stone but it seems pretty crazy to me.  I am not sure of the pricing for this so-called certification process but I know one thing, "It can'y be cheap!".

At this point, you have to ask your customer or yourself, at what point do you seriously consider upgrading your fire life safety system?  I am reasonably sure the this testing process from UL will impact your customers budget as well as their schedule.

Like I said, earlier, this is just the word on the street and I cannot verify any of this information.  With that said, it is something to consider and look into if you are currently in this situation.

CCTV Cameras that Look Like Smoke Detectors are They Allowed?

Are CCTV Cameras inside of Smoke Detectors Allowed by Code?

There are a lot of people that asking me if it is permitted to install look-a-like devices along with an approved fire alarm system.  This is mainly the case with CCTV cameras designed to look like fire alarm system smoke detectors of smoke alarms.  Now to the trained eye of a seasoned technician, it is always easy to spot these devices as they do not look like any of the system smoke detector or smoke alarm brands we have grown accustom to.

Customers like these CCTV Smoke Detector devices because it gives them the sense of security without having to display an obvious CCTV camera.  Most of the time, I feel that these are used in the situation where an owner wants to keep an eye on his or her employees.   If the  CCTV camera is hidden inside of a smoke detector, then the employees would be unaware they are being filmed and may be caught performing unlawful acts and then fired.  In the case of preventing robbery I believe you should have an obvious CCTV camera in plain sight.  This will act as a deterrent and possibly prevent any acts of theft in the first place.

Now on to the question at hand.  Are these Smoke Detector Cameras permitted to be installed along side an approved fire alarm system?  Some people say no as they provide a false sense of security in the event of a fire emergency while others say it is just fine as it is not tied to or part of the system.

The International Fire Code 2015 (IFC) section 901.4.5 - Appearance of Equipment.  "Any device that has the physical appearance of a life safety or fire protection equipment that does not perform that life safety or fire protection function, shall be prohibited."

Now this is like anything else.  Always check with your local AHJ.  Typically these discrete Smoke Detector CCTV cameras will be installed after the initial fire alarm inspection and won't be seen by the AHJ.  If you notice one of these discrete smoke detector camera during a semi or annual fire alarm device test, note it down and discuss with the local AHJ.  I believe that if everyone is on the same page and you have it well documented in your Fire Alarm Inspection and Testing paperwork, then you are covered.


If you are interested in taking the NICET Test for "fire alarms" or "Inspection and Testing of Fire Alarms", then we have you covered!  We are now selling our CBT Levels 1 - 4 NICET practice test with preparation material.  This material is packed with tons of NICET practice test questions along with all code references as to where to find the answers.  We have also supplied the material with all of the necessary NICET applications, CBT calculator demonstrations, links and more.  If you need more information, feel free to send an email.  You can find the link to purchase our NICET Practice Test on the top left section of this site.

UUKL Smoke Control For Fire Alarms

UL (Underwriters Laboratories) has a section titled 864.  ANSI/UL-864 is the section that covers "Standards for Control Units and Accessories for Fire Alarms".  ANSI/UL 864 is currently on its 9th revision.  Published on September 30, 2003 with a current effective date of December 31, 2008, the new edition incorporates approximately 300 changes, including 100 pages of new requirements from the previous edition.


With that said, UUKL is a separate listing category under UL 864.  Control devices used in smoke control systems have a UUKL listing.  UL's UUKL listing is a category under UL 864, Control Units and Accessories for Fire Alarm Systems.  UUKL is for products covered under the description "Smoke Control Equipment."  Equipment that receives UL's UUKL rating has been tested for integrity and long term reliability.  The equipment is subjected to extreme temperatures, humidity  and electrical transients and surges. This testing ensures that the devices will continuously perform even under severe and abnormal conditions.

A UUKL Smoke Control System is a combination of fan, dampers, warning devices, relays and modules that all work together to perform the containment function of any smoke event at any location in a building.  If the UUKL Smoke Control System is design correctly it should inhibit and or prevent the movement of smoke into areas leading to exits or other areas designated safe zones in a building.

Read more about UUKL Smoke Control Panels HERE.


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Fire Sprinkler Waterflow, Tamper, OS&Y & Backflow | Fire Alarm Guide

Fire Alarms Online • Sprinkler Monitoring Guide
Waterflow switches, tamper switches, OS&Y valves and backflow preventers are commonly found around fire sprinkler risers, but they do not perform the same jobs. This guide explains what each component does and what the fire alarm system actually monitors.

Understanding Fire Sprinkler Monitoring

Fire alarm technicians routinely encounter sprinkler equipment without necessarily working on the hydraulic side of the sprinkler system.

Four terms come up constantly:

• Waterflow switch
• Tamper or valve supervisory switch
• OS&Y valve
• Backflow preventer

These components can be located close together, but each performs a different function.

The quickest way to understand the riser:

Waterflow switch: Detects sprinkler-system operation.
Tamper switch: Supervises the position of a control valve.
OS&Y: A type of indicating gate valve.
Backflow preventer: Protects the water supply against reverse flow.

What Is a Wet Pipe Sprinkler System?

A wet pipe sprinkler system normally contains pressurized water throughout the sprinkler piping.

When sufficient heat operates an automatic sprinkler, water discharges through that sprinkler and sustained water movement occurs through the system.

That water movement can operate a waterflow alarm-initiating device monitored by the fire alarm system.

For the complete operating sequence, see: Wet Pipe Fire Sprinkler Systems | How They Work →

What Is a Fire Sprinkler Waterflow Switch?

A waterflow switch detects the applicable waterflow condition associated with sprinkler-system operation.

On many wet pipe systems, this is accomplished with a vane- or paddle-type device mounted directly to the sprinkler piping.

A paddle extends into the water-filled pipe. When sufficient sustained water movement occurs, the paddle moves and operates the switch mechanism.

Sprinkler Operates → Water Moves → Paddle Moves → Waterflow Switch Operates → FACU Receives Alarm

We have an entire guide dedicated to the internal operation, retard and testing of this device: Fire Sprinkler Waterflow Switch | How It Works & Fire Alarm Monitoring →

Is Waterflow an Alarm or Supervisory Signal?

Sprinkler waterflow is an alarm function.

This is one of the most important distinctions for fire alarm technicians.

When the sprinkler waterflow alarm-initiating device operates, the fire alarm system processes the sprinkler waterflow as an alarm condition according to the approved system design.

A valve tamper condition is different.

Device	What It Detects	Fire Alarm Function
Waterflow Switch	Required sprinkler waterflow condition	Alarm
Valve Supervisory / Tamper Switch	Control valve moved from its normal position	Supervisory

What Is a Fire Sprinkler Tamper Switch?

The term tamper switch is commonly used in the field for a sprinkler valve supervisory switch.

Its purpose is to monitor the position of a valve controlling the sprinkler water supply.

If the valve moves sufficiently from its normal position, the supervisory switch changes state and the fire alarm system can receive a supervisory signal.

Important: A tamper switch does not normally detect waterflow. It monitors the position of a valve that can affect the availability of the sprinkler water supply.

Why Are Sprinkler Control Valves Supervised?

An automatic sprinkler system cannot provide its intended protection if a critical water-supply control valve has been improperly closed.

Electrical supervision allows movement of a monitored control valve from its normal position to create a supervisory condition at the fire alarm system.

That gives building personnel, service personnel or the supervising station an opportunity to investigate the condition before the sprinkler system is needed during a fire.

What Does OS&Y Mean?

OS&Y means Outside Screw and Yoke.

An OS&Y valve is a type of gate valve commonly encountered in fire protection water-supply arrangements.

One useful feature of this valve design is its visible stem.

As the valve is opened, the stem extends outward. As the valve is closed, the stem moves inward.

This gives technicians and inspectors a visible indication of valve position.

How Does an OS&Y Tamper Switch Work?

A listed OS&Y supervisory switch mounts to the valve and mechanically monitors movement of its stem.

A common arrangement uses a trip rod positioned in a groove on the valve stem when the valve is fully open.

When the valve begins moving away from its normal position, movement of the stem displaces the trip rod and changes the state of the supervisory switch contacts.

OS&Y Valve Moves → Supervisory Switch Operates → Monitor Module/Input Changes State → FACU Receives Supervisory Signal

Technician Tip: The OS&Y is the valve. The device mounted to it is the valve supervisory switch. In field conversation you may hear the entire arrangement called an "OS&Y tamper."

Is an OS&Y Valve a Backflow Preventer?

No.

This is a surprisingly common terminology mistake.

An OS&Y valve and a backflow preventer can both be part of the sprinkler water-supply arrangement, but they perform different functions.

An OS&Y valve is an indicating gate valve used to control water flow.

A backflow prevention assembly is intended to prevent unwanted reverse flow from the fire protection system toward the supplying water system.

Common Mistake: Do not use "backflow preventer" and "OS&Y" as two names for the same device. They are not synonymous.

What Is a Fire Sprinkler Backflow Preventer?

A backflow prevention assembly protects the supplying water system against reverse flow from the fire protection system.

The exact assembly used depends on the water-supply arrangement and applicable requirements.

Depending on the installation, a backflow assembly can have control valves that also require electrical supervision.

That is one reason fire alarm technicians frequently see supervisory switches physically located around a backflow assembly.

Does a Backflow Preventer Stop False Waterflow Alarms?

That should not be considered the primary purpose of a backflow preventer.

Its primary function is backflow protection.

Water-supply pressure fluctuations and transient movement can influence sprinkler alarm equipment, but those hydraulic effects should not be confused with the fundamental purpose of the backflow prevention assembly.

Can a Backflow Preventer Have Tamper Switches?

Yes. Control valves associated with a backflow assembly can be equipped with listed supervisory switches where valve-position supervision is required.

Depending on the valve style, different supervisory devices can be used.

For example, fire protection systems can use supervisory switches designed for:

• OS&Y gate valves
• Butterfly valves
• Post indicator valves
• Other listed valve arrangements

The important concept is that the switch must be appropriate for the valve and installed according to its listing and manufacturer's instructions.

What Is a Butterfly Valve Tamper Switch?

Not every supervised sprinkler valve is an OS&Y.

Butterfly valves are also commonly encountered in sprinkler systems and can incorporate or accept listed supervisory switches that monitor valve position.

From the fire alarm system's perspective, the objective is similar:

Valve Moves From Normal Position → Supervisory Device Operates → FACU Receives Supervisory Signal

The mechanical method used to monitor the valve depends on the valve and supervisory device.

What Is a Post Indicator Valve?

A Post Indicator Valve, or PIV, is another type of indicating control-valve arrangement commonly associated with fire protection water supplies.

A PIV provides a visible indication of whether the valve is open or shut.

Where electrical supervision is required, listed supervisory equipment can monitor movement of the valve from its normal position.

OS&Y valves, butterfly valves and PIVs may look completely different, but from the fire alarm technician's perspective the question remains:

What valve is being supervised, and what signal should the FACU receive when it moves from normal?

How Are Tamper Switches Connected to a Fire Alarm System?

On an addressable fire alarm system, dry contacts from the valve supervisory device are commonly connected to an addressable monitor or input module.

The basic sequence is:

Valve Supervisory Switch → Monitor Module → SLC → FACU → Supervisory Signal

The exact wiring depends on the fire alarm manufacturer, module, pathway configuration and approved design.

On conventional systems, valve supervisory contacts can instead be connected to an appropriate initiating circuit according to the listed fire alarm system design.

How Should Sprinkler Tamper Points Be Labeled?

Clear point descriptions matter.

A point labeled only:

TAMPER

does not tell responding personnel very much in a large building.

Where the system and approved documentation allow, descriptions should identify the actual valve or area being supervised.

Examples might include:

• SPRINKLER MAIN CONTROL VALVE
• 1ST FLOOR SPRINKLER VALVE TAMPER
• 2ND FLOOR EAST SPRINKLER TAMPER
• BACKFLOW CONTROL VALVE SUPERVISORY
• PARKING GARAGE SPRINKLER VALVE

Specific descriptions can save a tremendous amount of time during service calls and emergency response.

How Fast Should a Tamper Switch Operate?

A valve supervisory device is intended to identify movement of the monitored valve from its normal position before the valve reaches a condition that could significantly impair the sprinkler water supply.

The exact operating criteria depend on the applicable code, valve type, supervisory device and installation.

Technicians should therefore verify operation using the applicable requirements and manufacturer's instructions rather than creating an arbitrary number of valve turns for every installation.

Waterflow Retard vs Tamper Switch Operation

Another common mistake is applying waterflow-switch thinking to valve supervision.

A waterflow switch can incorporate a retard intended to reduce unwanted alarms from brief water movement.

A valve supervisory switch performs a completely different function: detecting abnormal movement of a monitored valve.

Do not add an arbitrary waterflow-style delay to a sprinkler supervisory point simply because both devices happen to be located on the same riser.

What About the 90-Second Waterflow Requirement?

The familiar 90-second waterflow requirement applies to waterflow alarm initiation under the applicable sustained-flow criteria.

It does not mean every waterflow switch should simply be adjusted to delay for 90 seconds.

Remember: 90 seconds is a maximum alarm-initiation period under the applicable waterflow criteria, not a universal target retard setting.

For the detailed explanation, see: Fire Sprinkler Waterflow Switch | Retard, Testing & Fire Alarm Monitoring →

Does One Sprinkler Cause Every Sprinkler to Open?

No.

In a conventional wet pipe sprinkler system using automatic sprinklers, individual sprinklers operate when sufficient heat reaches their heat-responsive elements.

One sprinkler operating does not electrically command every other sprinkler in the building to open.

Additional sprinklers operate only if conditions at those sprinklers cause their individual heat-responsive elements to operate.

Hollywood vs Reality: Pulling a manual fire alarm box also does not normally make every automatic sprinkler in a wet pipe system start dumping water. Movies owe quite a few fictional hotel owners new carpeting.

What Should a Fire Alarm Technician Check at a Sprinkler Riser?

When troubleshooting sprinkler monitoring, identify each component before touching wiring or programming.

A useful sequence is:

1. Identify the sprinkler-system type.
2. Identify the waterflow alarm device.
3. Identify each supervised control valve.
4. Determine what each switch physically monitors.
5. Identify the associated fire alarm monitor module or circuit.
6. Verify the point description at the FACU.
7. Verify whether the point should create alarm, supervisory or trouble.
8. Functionally test the actual monitored condition using the approved procedure.

Fire Alarm Technician's Field Rule: Never identify a sprinkler input solely by the wires connected to it. Follow the wiring to the physical device and determine what that device actually monitors. The mechanical function tells you what the electrical signal is supposed to mean.

Common Sprinkler Monitoring Mistakes

• Calling a backflow preventer an OS&Y.
• Calling every sprinkler valve an OS&Y.
• Programming waterflow as supervisory.
• Programming a valve tamper as a fire alarm.
• Assuming a backflow preventer's primary purpose is preventing false waterflow alarms.
• Assuming every supervised valve uses the same type of tamper switch.
• Labeling every sprinkler supervisory point simply "TAMPER."
• Setting every waterflow retard to 90 seconds.
• Testing only the electrical contacts instead of the actual monitored condition.
• Assuming one automatic sprinkler operating causes every sprinkler to discharge.

Wet, Dry and Deluge Systems Use Different Monitoring Arrangements

The equipment discussed in this guide is commonly encountered on wet pipe systems, but technicians should not assume the same waterflow arrangement is used on every sprinkler-system type.

Dry pipe systems commonly add pneumatic-pressure supervision and can use pressure-operated alarm devices associated with the dry pipe valve.

Deluge systems add another layer because detection, releasing circuits, releasing devices and valve operation can all become part of the sequence.

Continue through the sprinkler-system series:

• Wet Pipe Fire Sprinkler Systems | How They Work
• Dry Pipe Fire Sprinkler Systems | How They Work
• Deluge Fire Sprinkler Systems | How They Work & Fire Alarm Releasing

Frequently Asked Questions

Is an OS&Y a backflow preventer?

No. OS&Y stands for Outside Screw and Yoke and describes a type of indicating gate valve. A backflow prevention assembly performs a separate function by protecting the water supply against reverse flow.

What does a sprinkler tamper switch do?

A valve supervisory or tamper switch monitors the position of a sprinkler control valve. Movement from the normal position causes the switch to change state so the fire alarm system can receive a supervisory signal.

Is a sprinkler tamper switch an alarm?

A sprinkler control-valve supervisory switch normally initiates a supervisory signal, not a fire alarm signal.

Is sprinkler waterflow an alarm?

Yes. The required sprinkler waterflow condition is an alarm function.

What is the difference between a waterflow switch and a tamper switch?

A waterflow switch detects sprinkler-system waterflow. A tamper switch monitors the position of a sprinkler control valve.

What does OS&Y stand for?

OS&Y stands for Outside Screw and Yoke. It is a gate-valve configuration with an exposed stem that provides a visible indication of valve position.

Why does a backflow preventer matter on a sprinkler system?

Its purpose is to protect the supplying water system against reverse flow from the fire protection system. It should not be confused with the sprinkler waterflow alarm device or valve supervisory switch.

Can the valves on a backflow preventer be supervised?

Yes. Where required, control valves associated with a backflow assembly can be equipped with listed valve supervisory switches appropriate for the particular valve type.

Related Fire Sprinkler Guides

• Wet Pipe Fire Sprinkler Systems | How They Work
• Fire Sprinkler Waterflow Switch | How It Works & Fire Alarm Monitoring
• Dry Pipe Fire Sprinkler Systems | How They Work
• Deluge Fire Sprinkler Systems | How They Work & Fire Alarm Releasing

Studying for the NICET Fire Alarm Systems Exam?

Waterflow alarms, valve supervision, sprinkler interfaces and the difference between alarm and supervisory signals are fundamental concepts for fire alarm technicians.

Fire Alarms Online offers a 550-question NICET Fire Alarm Systems practice collection covering Levels I through IV, along with a free 35-question sample.

NICET Fire Alarm Practice Exams • Levels I–IV

Practice sprinkler monitoring, initiating devices, alarm and supervisory signals, code navigation, testing and troubleshooting.

View NICET Practice Exams →

Reviewing Sprinkler Interfaces in Bluebeam?

Waterflow switches, control-valve tampers, backflow assemblies and monitor modules should be clearly identified when reviewing fire alarm plans and sprinkler interface points.

Bluebeam Toolkit for Fire Alarm Professionals

Built for fire alarm layouts, takeoffs, estimating and faster PDF markup workflows.

View the Bluebeam Toolkit →

Bottom Line

The easiest way to understand sprinkler monitoring is to stop treating every device at the riser as the same thing.

A waterflow switch detects sprinkler-system operation and initiates an alarm. A tamper or valve supervisory switch monitors a sprinkler control valve and initiates a supervisory condition. An OS&Y is a type of indicating gate valve. A backflow preventer protects the supplying water system against reverse flow.

Once those four functions are separated, sprinkler monitoring becomes much easier to design, program, test and troubleshoot.

System Sensor D4120 Wiring | Duct Detector Wiring Guide

If you work in the fire alarm industry, chances are you have encountered a System Sensor D4120 4-wire conventional duct smoke detector. One of the most important wiring details with these detectors is properly supervising the detector when one or more D4120s are connected to a conventional IDC (Initiating Device Circuit) or an addressable monitor module.

This guide explains System Sensor D4120 wiring, including the alarm contacts, supervisory contacts, end-of-line (EOL) resistor, resettable power, and the proper concept for connecting multiple conventional duct smoke detectors to one IDC.

Important: This article explains the wiring concept using the System Sensor D4120 as the example. Always follow the current manufacturer's installation instructions, the fire alarm control panel or monitor-module instructions, equipment listings, applicable NFPA 72 requirements, and the AHJ-approved design for the specific installation.

System Sensor D4120 Duct Smoke Detector

The System Sensor D4120 is a conventional 4-wire photoelectric duct smoke detector designed for HVAC applications.

Unlike an addressable duct detector that communicates directly with an addressable fire alarm system, the conventional D4120 typically requires separate power and uses dry contacts to communicate alarm and supervisory conditions to the fire alarm control equipment.

This distinction is important because the IDC can remain electrically intact even while a separately powered detector has developed a problem. Proper supervision of the detector therefore matters just as much as supervision of the field wiring.

System Sensor D4120 Terminal Identification

For the wiring arrangement discussed in this article, the most important D4120 terminals are:

Function	D4120 Terminals
Alarm Contacts	4 (Common) and 5 (Normally Open)
Supervisory Contacts	3 (Common) and 14 (Normally Open)
24 VAC/DC Power	9 and 10
120 VAC Power	120 VAC input terminals

Do not confuse the alarm contacts with the supervisory contacts.

The alarm initiation contacts are associated with terminals 4 and 5, while detector supervision uses terminals 3 and 14.

Correction to the original 2013 article: An earlier version of this guide accidentally referred to supervisory terminals "#3 and #4" in one paragraph. The System Sensor D4120 supervisory contacts are terminals 3 and 14. Alarm initiation uses terminals 4 and 5.

System Sensor D4120 Alarm Contacts: Terminals 4 and 5

The D4120 provides alarm initiation contacts used to report an alarm condition to compatible fire alarm control equipment.

For the D4120:

• Terminal 4 = Alarm Common
• Terminal 5 = Alarm Normally Open

In standby, the normally open alarm contact remains open. When the duct detector enters alarm, the alarm contacts change state and can initiate an alarm through the connected IDC or monitor module, depending on the approved system design.

System Sensor D4120 Supervisory Contacts: Terminals 3 and 14

The D4120 also provides supervisory contacts that are extremely important when the detector is connected to a supervised fire alarm initiating circuit.

For the D4120:

• Terminal 3 = Supervisory Common
• Terminal 14 = Supervisory Normally Open

The manufacturer's wiring arrangement uses these contacts so a detector trouble condition can interrupt the supervised circuit and produce the appropriate trouble indication at the fire alarm control equipment.

This is particularly important with a 4-wire detector because detector operating power is separate from the initiating circuit.

Why a 4-Wire Duct Detector Must Be Properly Supervised

Imagine that the IDC wiring to a duct detector is perfectly intact, but the detector itself loses operating power.

If the installation only supervises the IDC wiring and does not properly account for detector integrity, the fire alarm panel could potentially see an electrically normal initiating circuit even though the detector is no longer capable of performing its intended detection function.

That is the problem the supervisory arrangement is intended to prevent.

Proper wiring allows a qualifying detector trouble condition to interrupt the supervised circuit so the fire alarm control equipment receives a trouble indication rather than silently leaving an impaired detector in service.

Where Does the D4120 End-of-Line Resistor Go?

The end-of-line resistor must be the value specified by the fire alarm control panel or monitor-module manufacturer.

It is not simply placed wherever it is physically convenient.

With the manufacturer's conventional 4-wire D4120 arrangement, the EOL resistor is located at the end of the supervised initiating circuit and the circuit is routed through the detector supervisory contacts as shown in the approved System Sensor wiring diagram.

This allows the circuit to supervise more than just continuity of the alarm-contact wiring.

Field Rule: The EOL resistor belongs at the electrically supervised end of the circuit, not inside the panel simply because it is easier to install there.

How to Wire One System Sensor D4120 to an IDC

At a conceptual level, a conventional D4120 installation involves three separate functions:

1. Operating power for the detector
2. Alarm initiation through the alarm contacts
3. Detector/circuit supervision through the required supervisory arrangement

When 24-volt power is used, the D4120 power input is connected at terminals 9 and 10 in accordance with the manufacturer's instructions.

The alarm initiation portion uses terminals 4 and 5.

The supervisory portion uses terminals 3 and 14.

The EOL resistor value and IDC wiring configuration must match the connected fire alarm control panel or monitor module.

How to Wire Multiple D4120 Duct Detectors on One IDC

This is where installers can get into trouble.

When multiple conventional D4120 duct detectors share one initiating circuit, the goal is not merely to make every detector capable of initiating an alarm. The installation must also maintain the required supervision of the detectors and field wiring.

Simply connecting the alarm contacts of several detectors and placing the EOL resistor at the final detector without following the manufacturer's supervisory arrangement can leave earlier detectors inadequately supervised.

Conceptually, the installation must maintain:

• The alarm initiating path through the required alarm contacts
• The supervisory path through the required detector supervisory contacts
• The separate operating-power circuit
• The EOL device at the electrically supervised end of the initiating circuit

Example: Three D4120 Duct Detectors on One Monitor Module

Assume three conventional D4120 duct smoke detectors are connected to one compatible addressable monitor module.

All three detectors need to be capable of initiating the intended alarm condition.

But now imagine:

• D4120 #1 develops a qualifying trouble condition
• D4120 #2 loses operating power
• D4120 #3 remains completely normal

If the wiring arrangement only provides effective detector supervision at the final detector, the fire alarm system may not receive the intended trouble indication from the first two detectors.

That is precisely why the supervisory path must be carried through the detectors in accordance with the manufacturer's approved wiring arrangement rather than treating the EOL resistor as nothing more than a device placed at the last physical box.

Do Not Loop Wire Under the D4120 Terminals

There is another small installation detail that matters tremendously for supervision.

Do not simply loop an unbroken conductor underneath a terminal screw.

System Sensor instructs installers to break the wire run at the detector terminals so the connection itself remains supervised.

If an installer loops a continuous conductor underneath a terminal and the terminal connection becomes loose, the circuit can potentially remain electrically continuous while the detector itself is disconnected from the circuit.

Breaking the conductor and terminating both ends properly makes the detector connection part of the supervised pathway.

D4120 vs. DH100ACDCLP Wiring

The D4120 replaced older System Sensor duct detector models including the DH100ACDCLP.

One helpful feature for technicians familiar with the older detector is that System Sensor retained several important terminal assignments.

Function	DH100ACDCLP	D4120
Alarm Contacts	4–5	4–5
Supervisory Contacts	3–14	3–14

That continuity made replacement work easier for technicians already familiar with the DH100 series.

However, never assume that an old detector can be replaced solely by matching terminal numbers. Verify the complete current installation instructions, voltage, accessories, relay functions, equipment compatibility, and approved system design.

Watch the Original D4120 Wiring Video

The following Fire Alarms Online video demonstrates the concept of wiring multiple conventional System Sensor D4120 duct smoke detectors while maintaining proper alarm and supervisory circuit integrity.

What Happens If Only the Last Duct Detector Is Properly Supervised?

This was the central lesson of the original Fire Alarms Online article.

Suppose several duct detectors have their alarm contacts connected to the same initiating circuit, but the supervisory arrangement is applied incorrectly so only the final detector effectively controls circuit supervision.

The detectors might still initiate alarms correctly.

That does not necessarily mean the installation is properly supervised.

A problem affecting an earlier detector could potentially go unreported if the circuit arrangement does not monitor that detector's integrity as intended.

Alarm operation and trouble supervision are two different functions. Both have to work.

Should You Meter the D4120 Contacts?

A meter can be extremely useful when troubleshooting or verifying dry-contact operation, but technicians should begin with the manufacturer's terminal diagram rather than guessing based on normally open or normally closed labels.

Relay and supervisory contact diagrams are typically shown in a defined equipment state, and contacts can change state when the detector is powered, normal, in alarm, or experiencing a trouble condition.

Before altering field wiring:

• Verify the manufacturer's terminal diagram
• Identify the contact common
• Identify normally open and normally closed contacts
• Verify the detector's current operating state
• Use the meter to confirm the expected contact state

This is particularly important when troubleshooting older installations or equipment from different manufacturers.

D4120 Alarm Contacts vs. Auxiliary Contacts

The D4120 contains additional relay contacts that can be used for approved auxiliary functions such as HVAC fan shutdown.

These should not be confused with the alarm initiation contacts used to communicate with the fire alarm control equipment.

System Sensor specifically distinguishes the detector's alarm initiation contacts, supervisory contacts, and auxiliary relay contacts in its wiring documentation.

Always use the contacts intended for the required function.

Duct Detector Fan Shutdown Wiring

Duct smoke detectors are commonly associated with HVAC shutdown, but the required control arrangement depends on the mechanical system, applicable code, fire alarm sequence of operations, and approved design.

A duct detector can provide relay contacts for an approved HVAC control function, but the fire alarm initiating circuit and the fan shutdown circuit serve different purposes.

Do not treat the HVAC shutdown relay wiring as a substitute for properly reporting the detector condition to the fire alarm system where such reporting is required.

Testing the System Sensor D4120 After Wiring

After installation, the detector and associated fire alarm functions should be tested to verify the intended sequence of operation.

Depending on the installation, testing can include verifying:

• Normal detector power
• Alarm initiation at the FACP
• Detector trouble indication
• Loss-of-power supervision
• Remote test/reset functions where provided
• HVAC shutdown or other required control functions
• Restoration after reset
• Proper air sampling through the duct detector

Duct-type smoke detector testing is more than simply introducing smoke into the detector. Sampling-tube installations must also be capable of properly sampling the HVAC airstream.

For the complete procedure, see:

How to Test a Duct Smoke Detector With a Manometer

Common D4120 Wiring Mistakes

• Using the wrong supervisory terminals. D4120 supervision uses terminals 3 and 14.
• Confusing alarm and supervisory contacts. Alarm initiation uses terminals 4 and 5.
• Installing the EOL resistor at the panel. This defeats supervision of the field circuit beyond that point.
• Supervising only the last detector. Multiple separately powered detectors must be wired using the approved supervisory arrangement.
• Looping an unbroken wire under detector terminals. Break the conductor at supervised terminals as required by the manufacturer.
• Assuming all manufacturers use the same terminals. They do not.
• Using auxiliary contacts as alarm initiation contacts. Verify the function of every relay terminal.
• Ignoring detector operating power. A 4-wire detector uses a separate power circuit that must be considered in the supervision strategy.
• Assuming alarm testing proves supervision. Test alarm and trouble conditions separately.

System Sensor D4120 Wiring Quick Reference

Detector	System Sensor D4120
Detector Type	Conventional 4-wire photoelectric duct smoke detector
Alarm Contacts	4 Common / 5 Normally Open
Supervisory Contacts	3 Common / 14 Normally Open
24 VAC/DC Power	9 and 10
EOL Resistor	Value specified by connected fire alarm control equipment
Legacy Model	DH100ACDCLP and related DH100 series applications

Frequently Asked Questions

What terminals are the alarm contacts on a System Sensor D4120?

The D4120 alarm initiation contacts are terminals 4 and 5. Terminal 4 is common and terminal 5 is normally open for the alarm initiation contact arrangement discussed here.

What terminals are the supervisory contacts on a D4120?

The System Sensor D4120 supervisory contacts used in the manufacturer's conventional 4-wire system wiring diagram are terminals 3 and 14. Terminal 3 is common and terminal 14 is normally open.

What terminals provide 24-volt power to the D4120?

The D4120 accepts 24 VAC/DC operating power at terminals 9 and 10. Follow the manufacturer's instructions for the specific power source and installation.

Can multiple D4120 duct detectors be connected to one IDC?

Multiple conventional duct detectors can be used on a compatible initiating circuit when permitted by the connected equipment and when wired according to the manufacturer's approved arrangement. Detector supervision, circuit limitations, EOL placement, power requirements, and control-panel compatibility must all be considered.

Where should the EOL resistor be installed?

The EOL resistor must be located at the electrically supervised end of the initiating circuit and be the resistance value specified by the connected fire alarm control equipment. For D4120 installations, follow the manufacturer's wiring diagram so detector supervision is maintained.

Is the D4120 a 2-wire or 4-wire duct detector?

The System Sensor D4120 discussed in this article is a 4-wire conventional duct smoke detector. Its operating power is separate from its alarm initiating contacts.

Did the D4120 replace the DH100ACDCLP?

The D4120 succeeded older System Sensor conventional duct detector products including the DH100ACDCLP. System Sensor retained alarm terminals 4–5 and supervisory terminals 3–14 between these models, which helped simplify many replacement applications.

Does a duct smoke detector replace open-area smoke detection?

No. A duct smoke detector is intended to detect smoke within an HVAC duct system for its listed application. It is not a general substitute for open-area smoke detection required elsewhere in a building.

Related Fire Alarm Guides

• How to Test a Duct Smoke Detector With a Manometer
• NEC Article 760 Fire Alarm Wiring Requirements
• Fire Alarm Ground Fault Troubleshooting

Final Thoughts

The most important lesson when wiring conventional System Sensor D4120 duct smoke detectors is that getting an alarm at the panel is not the same thing as having a properly supervised circuit.

The D4120 alarm initiation contacts are 4 and 5, while the supervisory contacts are 3 and 14. When multiple separately powered duct detectors share an IDC or compatible monitor module, the complete wiring arrangement must maintain the required supervision of the detectors and field wiring.

Follow the System Sensor wiring diagram, use the EOL resistance specified by the connected fire alarm control equipment, break field conductors at supervised terminals rather than looping them underneath terminals, and test both alarm and trouble conditions when commissioning the system.

Technical Disclaimer: This article is provided for educational and troubleshooting purposes. Always follow the current System Sensor installation instructions, fire alarm control panel or module documentation, equipment listings, approved sequence of operations, applicable NFPA 72 requirements, adopted codes, and AHJ requirements. Disconnect and secure applicable power sources before performing wiring work.

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