Fire/Alarm Flow Switch

[Angel Electric]

Flow switch for a sprinkler system riser. Which is correct N/O or N/C?

 

[cadpoint]

Here's my gut response.

Isn't the system like a phone you have a open line that one closes when reporting or using...

 

[Angel Electric]

Good sence!

Good sence!

A Fellow fire tech explained to me that the contacts are open with a risistor in line ... When water flows the flow switch closes and it shunts the data circuit causing the fire alarm panel to go into Alarm, I guess im just going for second perspective of how the switch works and its purpose in what it is controling.?

 

[stevebea]

A Fellow fire tech explained to me that the contacts are open with a risistor in line ... When water flows the flow switch closes and it shunts the data circuit causing the fire alarm panel to go into Alarm, I guess im just going for second perspective of how the switch works and its purpose in what it is controling.?

The FACP is looking for a particular resistance value and when that changes whether it's the switch closing, cable shorted, or cable opens up, it will show up as a trouble.

 

[Angel Electric]

contact held open

contact held open

should you have it closed or open

 

[infinity]

I haven't done much fire alarm in recent years but in the old days a water flow switch as an initiation device would be wired N/O with a resistor across the contacts. Water flow would close the switch, shunt the resistor and send the system into an alarm condition. If the wiring became broken or a wire came off of a terminal then the FACP would not read the resistor and would show a trouble alarm. This may all have changed now with addressable devices.

 

[MichaelGP3]

I haven't done much fire alarm in recent years but in the old days a water flow switch as an initiation device would be wired N/O with a resistor across the contacts. Water flow would close the switch, shunt the resistor and send the system into an alarm condition. If the wiring became broken or a wire came off of a terminal then the FACP would read no resistance and would show a trouble alarm. This may all have changed now with addressable devices.

If the wire became broken or came loose from a terminal, the FACP would read infinite resistance and show a trouble. No resistance across the waterflow contacts would be an alarm (not a trouble), regardless of whether the system used traditional zone cards or addressable modules.

I've found it helpful to steer clear of the phrase 'trouble alarm'. Trouble signal or trouble condition leads to less confusion in my opinion.

 

[infinity]

If the wire became broken or came loose from a terminal, the FACP would read infinite resistance and show a trouble. No resistance across the waterflow contacts would be an alarm (not a trouble), regardless of whether the system used traditional zone cards or addressable modules.

I've found it helpful to steer clear of the phrase 'trouble alarm'. Trouble signal or trouble condition leads to less confusion in my opinion.

Yes, you're correct I should have said that that the FACP would not red the resistor. As You've pointed out an open in the system would have near infinite resistance.

 

[nhfire77]

I've found it helpful to steer clear of the phrase 'trouble alarm'. Trouble signal or trouble condition leads to less confusion in my opinion.

That's like with a supervisory alarm. You almost always have to ask, is it a supervisory trouble or supervisory alarm? It really confuses the fire alarm newbie.

 

[Tcook002]

I've encountered this exact issue with other initiating devices (Specifically, heat detectors with normally closed contacts built into them)

Here is the code that was used on me by an AHJ regarding things wired normally closed:

NFPA 72 2007, section 4.4.7.1.14 - Interconnection means shall be arranged so that a single break or single ground fault does not cause an alarm signal.

 

[George Stolz]

Flow switch for a sprinkler system riser. Which is correct N/O or N/C?

When I start into a riser room, I intentionally start from scratch every time. I will test for continuity on the switches in their "natural" state, and then change states to "problem" and test again.

N/O and N/C are irrelevant and misleading. You want to use the contacts that are open in their "natural" state - the state they will be in for 99% of their life, the state that they will be in when everything is okay. For a flow switch, the natural state would be the state they are in when there is no water flowing. For a tamper, this is more complicated. Some valves may be closed in the system's natural state, and others will be open. You may need to coordinate with the sprinkler guy to be sure that you understand which is which.

Here is a diagram of a basic riser setup.

 

[hurk27]

We must also realize that not all areas of the country require a monitored alarm system with a sprinkled building, here it is common to find the N.O. contacts used to turn on a simple 120 volt horn mounted on the outside of the building, and maybe one inside.

The flow switch, pressure switch/clapper switch (Dry system) and valve tamper switch's are also wired in parallel to sound these same horns.

 

[MichaelGP3]

I can see the logic...

I can see the logic...

We must also realize that not all areas of the country require a monitored alarm system with a sprinkled building, here it is common to find the N.O. contacts used to turn on a simple 120 volt horn mounted on the outside of the building, and maybe one inside.

The flow switch, pressure switch/clapper switch (Dry system) and valve tamper switch's are also wired in parallel to sound these same horns.

but I haven't run across this scenario before (regarding tampers). I've only seen waterflow switch contacts wired to 120 volt AC bells (outside only) in lieu of mechanical water gongs. I've never run across dry systems that weren't monitored. All of my experience has been in Northern California, and I have by no means seen everything here. Is this covered in NFPA 13, or is the practice derived from local codes/amendments?

 

[iwire]

Do you guys do a lot of riser rooms without engineered drawings?

For us all of this will be clearly spelled out on the fire alarm details and we are expected to follow them.

 

[iwire]

Here is a typical detail off a recent print

 

[hurk27]

Do you guys do a lot of riser rooms without engineered drawings?

For us all of this will be clearly spelled out on the fire alarm details and we are expected to follow them.

Here any public building over 5k sf requires sprinkling, so we get quite a few systems that are not under a engineered drawing, but maybe a manufactures drawing used by the installers of the system, many of these are not monitored by FA systems and are stand alone with a 120 volt fire bell/horn, all require a fire department hook up for back up water supply, and most are dry systems because of the running of the pipes in the attic, they will have a very small low volume air compressor that maintains about 30# of air pressure on the dry side of the system that holds a clapper valve closed till a head is tripped, then the air bleeds off and the clapper valve opens and sends the water through the lines, there is also drain valves to reset the system at which time are re-tagged just like fire extinguishers along with test place cards at the main system location.

 

[MichaelGP3]

Here is a typical detail off a recent print

Woe be unto him who installs single gang boxes per your detail expecting the FMM-1 monitor module to fit.

 

[nhfire77]

Woe be unto him who installs single gang boxes per your detail expecting the FMM-1 monitor module to fit.

I would like to see what that looks like, as it would be funny.

 

[Angel Electric]

Gratitude

Gratitude

Thanks to all who havee shared! It makes being an Electrician a rewarding job when you can be taught new things... Stay safe....

 

[DM2-Inc]

The answer is "It Depends"

For some addressable systems, addressable modules have the ability to recognize a NC switch going open as an event. As others have explained, the system is looking for a change in resistance. For a NC contact going open, the panel sees a short as a normal condition. When the contact changes to NO, the addressable module would see the "End-of-Line" (EOL) resistor and signal the change of device state. If the EOL is missing, the module will respond as if the wiring to the device has been compromised or damaged in some way.

Having said that, most addressable systems will want the contact to be NO and Close upon water flow.

For "Non-Addressable" systems your only choice would be a NO contact going closed.

In all cases the EOL is technically placed in "Parallel" on the circuit, across the two screw terminals in the flow switch.

On older systems it was acceptable to wire the "Tamper Switch" in series with the EOL and down stream of the flow switch. This insured that an "ALARM" from the flow switch would override a "Trouble" from the Tamper switch. In this particular case, some might say it doesn't matter because if the valve is closed, you don't have the ability to have water flow. However consider a faulty tamper switch and if wired ahead of the flow switch, activation of the flow switch wouldn't be seen by the circuit.

This changed a number of years ago. The code now requires the ability to distinguish the difference between a fault on the wiring and the activation of a device. This coupled with the requirement that tamper switches are required to signal a "Supervisory" condition at the panel, not a "Trouble" condition.

While this may have muddied up the waters for this discussion, the proper connections should be noted on drawings.