Fire Alarm System Basic Wirirng

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This is a very basic question, but I need a basic explanation of how power is distributed throughout a standard fire alarm system. I know that constant AC power runs to the fire alarm control panel, but the rest I am not sure about. I know that initiating devices and notification appliances (i.e. inputs and outputs) are located throughout the zone/building. I do not know how they are connected to one another. More specifically, what type of cabling? Is it power limited (FPL), PLFP, PLFR? Or am I not on the right track? Are the inputs and outputs daisy-chained together with an EOL resistor, or no? Does anyone have any basic feedback regarding the wiring layout. Thank you guys..
 

fmtjfw

Senior Member
This is a very basic question, but I need a basic explanation of how power is distributed throughout a standard fire alarm system. I know that constant AC power runs to the fire alarm control panel, but the rest I am not sure about. I know that initiating devices and notification appliances (i.e. inputs and outputs) are located throughout the zone/building. I do not know how they are connected to one another. More specifically, what type of cabling? Is it power limited (FPL), PLFP, PLFR? Or am I not on the right track? Are the inputs and outputs daisy-chained together with an EOL resistor, or no? Does anyone have any basic feedback regarding the wiring layout. Thank you guys..

There are several systems, 4-wire supervised and electronic supervision are two popular ones.

They are wired differently and might even use different types or wire.

Please be more specific.
 

iwire

Moderator
Staff member
Location
Massachusetts
As others have said that is a broad question there are many types of systems. I am on the job now adding born strobes to a fire system.
 
Have you looked at Art 760 ? There are lots of variables.

I have looked at Article 760 and that's why I pose the question. I do not need to know so much about non power-limited cabling or cables for plenum space. I really just need a dumbed-down explanation of how the devices are connected. I am not in the field of electric wiring or fire and life safety, but I have a basic understanding of how the system works (very basic).
 
As others have said that is a broad question there are many types of systems. I am on the job now adding born strobes to a fire system.

The question is broad. The problem is that Article 760 focuses on 3 main PLFA circuits and how they are to be installed in raceways, enclosures, etc. What would help me is if I could remove the raceway/enclosure on a wall that covers the cables that run from the pull station, up to the strobe, and then into/above the suspended ceiling. In that case, I literally just would like to know how many cables there are, how they are connected to the devices, and where they run to in the ceiling. Hopefully that clears up my train of thought. Thanks
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I would suggest you get a copy of NTC's Brown Book, available on Amazon. It is a good practicle reference.
 

fmtjfw

Senior Member
Traditional 4 wire system

Traditional 4 wire system

There are three kinds of loops detectors, sprinker, and signaling devices.

Detector loops conductors loop through each device, that is two conductors from the central control box side come in and two conductor to the next device or end-of-line (EOL) resistor go out. The wires must be cut and terminated at each device.The polarity of the devices must be preserved unless they are simple pull stations or other NO contact devices. Devices that use power, smoke detectors for instance, require proper polarity. No TEE taps are allowed. To reset the electronic detectors, the central control box interrupts the supply to a loop for a short time.

The central control box looks for three possible signals:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) SHORT -- alarm -- a device has signaled fire.

Sprinkler loops send to the central control box:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) other resistance level -- trouble -- sprinkler valve may be closed
4) SHORT -- sprinkler in operation -- alarm condition

The alarm loops also loop through each device as above. The EOL value may be the same as detector loop, or much lower. The central control box normally supplies the signalling loop with reverse voltage. To initiate the alarm signals, the central box reverses the voltage (to normal) which causes the alarms to sound and/or flash. The individual alarm devices are furnished with a diode (or its equivalent) which detects the polarity. When the central control box does not send out the alarm signal, it looks for two possible signals:

1) OPEN or SHORTED -- trouble -- loop compromised.
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition


The central box also looks for ground faults on these loop. It also looks for loss of commercial power. Boxes are typically supplied with 24 hour? battery supplies trickle charged from commercial power.

The central control box often also controls the power to:

1) large HVAC equipment controls to shut it down on alarm
2) fire-door magnetic holders to close doors on alarm conditions (not supervised, fails safe with doors closed).
3) Magnet door locks to release door locks on alarm conditions (not supervised, fails safe with doors unlocked).

This is a brief summary of the 100--200 pages of instructions usually provided.

NOTE: every new central control box must come with "complete" instructions. Read them until you understand them before doing an installation. Old central control boxes should have the instructions available for them at the work site, if not contact the manufacturer for a copy.

Devices like light beam smoke detectors usually have additional requirements which will be in their instructions.

There are also interconnections for hood extinguishing systems, hood exhaust fans, kitchen makeup (air from outside to inside) fans....
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
There are three kinds of loops detectors, sprinker, and signaling devices.

Detector loops conductors loop through each device, that is two conductors from the central control box side come in and two conductor to the next device or end-of-line (EOL) resistor go out. The wires must be cut and terminated at each device.The polarity of the devices must be preserved unless they are simple pull stations or other NO contact devices. Devices that use power, smoke detectors for instance, require proper polarity. No TEE taps are allowed. To reset the electronic detectors, the central control box interrupts the supply to a loop for a short time.

The central control box looks for three possible signals:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) SHORT -- alarm -- a device has signaled fire.

Sprinkler loops send to the central control box:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) other resistance level -- trouble -- sprinkler valve may be closed
4) SHORT -- sprinkler in operation -- alarm condition

The alarm loops also loop through each device as above. The EOL value may be the same as detector loop, or much lower. The central control box normally supplies the signalling loop with reverse voltage. To initiate the alarm signals, the central box reverses the voltage (to normal) which causes the alarms to sound and/or flash. The individual alarm devices are furnished with a diode (or its equivalent) which detects the polarity. When the central control box does not send out the alarm signal, it looks for two possible signals:

1) OPEN or SHORTED -- trouble -- loop compromised.
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition


The central box also looks for ground faults on these loop. It also looks for loss of commercial power. Boxes are typically supplied with 24 hour? battery supplies trickle charged from commercial power.

The central control box often also controls the power to:

1) large HVAC equipment controls to shut it down on alarm
2) fire-door magnetic holders to close doors on alarm conditions (not supervised, fails safe with doors closed).
3) Magnet door locks to release door locks on alarm conditions (not supervised, fails safe with doors unlocked).

This is a brief summary of the 100--200 pages of instructions usually provided.

NOTE: every new central control box must come with "complete" instructions. Read them until you understand them before doing an installation. Old central control boxes should have the instructions available for them at the work site, if not contact the manufacturer for a copy.

Devices like light beam smoke detectors usually have additional requirements which will be in their instructions.

There are also interconnections for hood extinguishing systems, hood exhaust fans, kitchen makeup (air from outside to inside) fans....

You have skipped the difference between Class "A" and Class "B" loops and the difference between indicating device circuits (IDC) for conventional devices and signal line circuits (SLC) for analog addressable devices. Not to mention voice circuits. This of course would make an even longer post, which is why I suggested he pick up a good reference. Given the OP's starting point, whatever we tell him in a post is way less than what he needs to develop a good understanding of fire alarm circuits.

By the way, if I understand your description of sprinkler loops correctly, you are daisy-chaining the flows and tampers which isn't really allowed. NFPA requires a distinct signal for supervisory events. There is no way to tell a supervisory (valve tamper) from a trouble by wiring the tamper in series with the flow.
 

fmtjfw

Senior Member
Only describing one type of fire alarm circuit -- see title of post

Only describing one type of fire alarm circuit -- see title of post

You have skipped the difference between Class "A" and Class "B" loops and the difference between indicating device circuits (IDC) for conventional devices and signal line circuits (SLC) for analog addressable devices. Not to mention voice circuits. This of course would make an even longer post, which is why I suggested he pick up a good reference. Given the OP's starting point, whatever we tell him in a post is way less than what he needs to develop a good understanding of fire alarm circuits.

By the way, if I understand your description of sprinkler loops correctly, you are daisy-chaining the flows and tampers which isn't really allowed. NFPA requires a distinct signal for supervisory events. There is no way to tell a supervisory (valve tamper) from a trouble by wiring the tamper in series with the flow.

The intent of the posting was to cover 90% of the circuit knowledge for a person replacing devices on a typical 4 wire system. This is what we [try to] teach electricians new to fire alarms before they go off to replace smokes, heats, pull stations, horns, and strobes. We do not teach them hoods, sprinklers, dialers, annunciators or elevator controls ...

Please read the sprinkler loop description again.

The sprinkler signal devices I am familiar with have a EOL, a different resistor in series with the tamper switch, and a NO contact across the line for flow. The listed control boxes I have installed have provisions for tamper/flow circuits as I described. See NFPA 72-2007 Figure C.2.15 for an example circuit.
 
Last edited:
There are three kinds of loops detectors, sprinker, and signaling devices.

Detector loops conductors loop through each device, that is two conductors from the central control box side come in and two conductor to the next device or end-of-line (EOL) resistor go out. The wires must be cut and terminated at each device.The polarity of the devices must be preserved unless they are simple pull stations or other NO contact devices. Devices that use power, smoke detectors for instance, require proper polarity. No TEE taps are allowed. To reset the electronic detectors, the central control box interrupts the supply to a loop for a short time.

The central control box looks for three possible signals:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) SHORT -- alarm -- a device has signaled fire.

Sprinkler loops send to the central control box:

1) OPEN -- trouble -- loop comprised
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition
3) other resistance level -- trouble -- sprinkler valve may be closed
4) SHORT -- sprinkler in operation -- alarm condition

The alarm loops also loop through each device as above. The EOL value may be the same as detector loop, or much lower. The central control box normally supplies the signalling loop with reverse voltage. To initiate the alarm signals, the central box reverses the voltage (to normal) which causes the alarms to sound and/or flash. The individual alarm devices are furnished with a diode (or its equivalent) which detects the polarity. When the central control box does not send out the alarm signal, it looks for two possible signals:

1) OPEN or SHORTED -- trouble -- loop compromised.
2) resistance roughly of the EOL -- OK -- loop is ok, no alarm condition


The central box also looks for ground faults on these loop. It also looks for loss of commercial power. Boxes are typically supplied with 24 hour? battery supplies trickle charged from commercial power.

The central control box often also controls the power to:

1) large HVAC equipment controls to shut it down on alarm
2) fire-door magnetic holders to close doors on alarm conditions (not supervised, fails safe with doors closed).
3) Magnet door locks to release door locks on alarm conditions (not supervised, fails safe with doors unlocked).

This is a brief summary of the 100--200 pages of instructions usually provided.

NOTE: every new central control box must come with "complete" instructions. Read them until you understand them before doing an installation. Old central control boxes should have the instructions available for them at the work site, if not contact the manufacturer for a copy.

Devices like light beam smoke detectors usually have additional requirements which will be in their instructions.

There are also interconnections for hood extinguishing systems, hood exhaust fans, kitchen makeup (air from outside to inside) fans....

I appreciate the response. This helps a lot.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
The intent of the posting was to cover 90% of the circuit knowledge for a person replacing devices on a typical 4 wire system. This is what we [try to] teach electricians new to fire alarms before they go off to replace smokes, heats, pull stations, horns, and strobes. We do not teach them hoods, sprinklers, dialers, annunciators or elevator controls ...

Please read the sprinkler loop description again.

The sprinkler signal devices I am familiar with have a EOL, a different resistor in series with the tamper switch, and a NO contact across the line for flow. The listed control boxes I have installed have provisions for tamper/flow circuits as I described. See NFPA 72-2007 Figure C.2.15 for an example circuit.

If you were intending to discuss 4-wire smoke detection, that bit got lost in your post. 4-wire smokes are powered from a separate resetable auxilliary power supply, typically the FACP's AUX POWER terminals but it could also be a separate listed power supply. It's definitely not the "loop".

I also challenge your assumption that this covers 90% of the circuit knowledge an electrician might need dealing with typical fire alarm installations you might run into today, especially commercial or industrial systems. 20 years ago, maybe, but not today. Perhaps they are more common in residential applications; we don't do a lot of resi.

For sprinkler, I don't know of any currently manufactured control panel that can distinguish a two-level fault based on resistance and route the input from the IDC to the trouble LED or supervisory LED as required. I don't claim to have seen it all, so if such a creature exists I'd be interested to know more.

On your Fig. C.2.15, see the explanatory note for the figure:

"Initiating Device Circuit with Parallel Waterflow
Alarm Switches and a Series Supervisory Valve Switch, Which No
Longer Meets the Requirements of NFPA 72
" [bold added]

They may be out there, but don't be putting in any new ones.
 

fmtjfw

Senior Member
If you were intending to discuss 4-wire smoke detection, that bit got lost in your post. 4-wire smokes are powered from a separate resetable auxilliary power supply, typically the FACP's AUX POWER terminals but it could also be a separate listed power supply. It's definitely not the "loop".

My bad terminology. I was describing wiring for "two-wire detectors". For some reason (perhaps the number of wires at each device) locally they are referred to as 4-wire.

I also challenge your assumption that this covers 90% of the circuit knowledge an electrician might need dealing with typical fire alarm installations you might run into today, especially commercial or industrial systems. 20 years ago, maybe, but not today. Perhaps they are more common in residential applications; we don't do a lot of resi.
Very common in old school buildings.
We got rid of our only really 4-wire system two years ago, now addressable system.

New systems are almost all addressable. Wiring an addressable is so much simpler than a 2/4-wire system. It does not require a different mindset from wiring ordinary power wiring.

For sprinkler, I don't know of any currently manufactured control panel that can distinguish a two-level fault based on resistance and route the input from the IDC to the trouble LED or supervisory LED as required. I don't claim to have seen it all, so if such a creature exists I'd be interested to know more.
Silent Knight conventional (non-addressable panels) see "Combination Waterflow/Supervisory Zone" (page 21)
https://www.silentknight.com/documentation/Documents/52604.pdf#21

On your Fig. C.2.15, see the explanatory note for the figure:

"Initiating Device Circuit with Parallel Waterflow
Alarm Switches and a Series Supervisory Valve Switch, Which No
Longer Meets the Requirements of NFPA 72
" [bold added]

They may be out there, but don't be putting in any new ones.
Thanks!
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
...Silent Knight conventional (non-addressable panels) see "Combination Waterflow/Supervisory Zone" (page 21)
https://www.silentknight.com/documentation/Documents/52604.pdf#21

...

Thanks back at you! We use Silent Knight products all the time, but almost never the SK-2/4. I was totally unaware of this feature:dunce:. On the other hand, I can't see why they left this in the product. They had to update the panel to meet the ninth edition of UL 864, and I'm almost positive NFPA 72 had forbidden this arrangement by then.
 

fmtjfw

Senior Member
Thanks back at you! We use Silent Knight products all the time, but almost never the SK-2/4. I was totally unaware of this feature:dunce:. On the other hand, I can't see why they left this in the product. They had to update the panel to meet the ninth edition of UL 864, and I'm almost positive NFPA 72 had forbidden this arrangement by then.

That was just the first manual I found.

We use larger versions of these for replacement panels in locations that have 2-wire supervised circuits. I don't know if you have to change the sprinkler arrangement on a replacement? Maybe that is why they left it in. Also maybe they are rated for Canada and different rules.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
That was just the first manual I found.

We use larger versions of these for replacement panels in locations that have 2-wire supervised circuits. I don't know if you have to change the sprinkler arrangement on a replacement? Maybe that is why they left it in. Also maybe they are rated for Canada and different rules.

I took a quick look at the 5208 manual, and there's nothing like the SK-2/4 arrangement illustrated in it. I think it's an interesting question and I'll raise it with my rep next time I talk to him. As for Canada, I've no clue.
 
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