7/26/2019 ABCS of Fire Alarm Part 5

1/2January/February 2010 Page 47

The ABCs of Fire Alarm Systems - Part VPutting It All Together

By Anthony J. Shalna 2009 Principal IMSA Representative to the Automatic Fire Alarm AssociationPresident: Southeastern Signalmen of Massachusetts

Approvals Manager: Gamewell-FCI by Honeywell

In previous articles we discussed the

re alarm control panel, devices thatplace it into alarm and the most com-mon devices that are turned on bythe panel. The main feature that distin-guishes a re alarm control panel fromburglar alarm or switching panels isthat the re alarm panel is supervised,which means that it has the ability tomonitor its own integrity.

Unlike the burglar alarm panel, whichhas only two conditions, normal andalarm, the fire alarm control has anumber of conditions or states. These

are: normal, alarm, trouble, and (fairlyrecently) supervisory. The normal andalarm states are obvious.

The supervisory state monitors sprin-kler devices so the panel can indicatethat a waterow device, such as gatevalve, is in an off-normal condition. It isdesirable to know that someone turnedoff the water supply to a sprinkler sys-tem (or forgot to turn it back on afterservice), but there is no need to createan alarm condition. Other supervisorydevices can monitor water tanks for

freezing, low or high water levels, etc.The supervisory condition results ina signal that differs from both alarmand trouble conditions, although thesupervisory condition may share thetrouble sounder.

The last state or condition is the troublecondition. This condition is character-ized by a yellow light on the panelaccompanied by the sounding of an au-dible device, such as a buzzer or piezo-electric sounder, which may be silencedor acknowledged temporarily. Uponcorrection of the trouble condition, thesounder will re-energize, indicatingthat the panel is back to normal. Re-turning the silencing switch to normalor pressing the acknowledgment buttonwill silence the sounder and return thepanel to a quiescent condition. This isknown as ring back, a phrase thatwas common in the past, but not usedvery frequently nowadays.

Trouble signals are caused by numer-ous things. Some of these are a break

in the eld wiring, AC power failure,

battery disconnection or failure, groundfaults, open fuses, removal of plug-indetectors, disarrangement of panelswitches, etc.

We have seen how supervised circuitsof conventional re alarm panels oper-ate with the aid of end of line devicesthat maintain a current ow throughthe supervised circuit. Addressablesystems operate in a different man-ner and will be the subject of a futurearticle. The current flow throughthe supervised field circuit must be

maintained through the eld wiring.This is why conventional fire alarmsystems must be wired in a prescribedmanner.

Terminations to a detector or appliancemust be made by cutting the eld wiresat their respective terminals. In otherwords, one wire must bring current intoa terminal of the detec-tor or appliance, and asecond wire must exitfrom the same terminaland connect to the next

device. See Figure 1.If a eld wire is not cut,bu t lo op ed arou nd ascrew, there will be nointerruption of the su-pervisory current shouldthe head of the screwshear off. The device willbe disconnected fromthe circuit but there willbe no trouble indication.The panel will neverknow that the deviceis disconnected. If the

eld wire is cut and bothends connected to twoseparate terminals, theshearing of a screw heador loss of a wire crimplug will cause the endsto separate and a troublecondition will immedi-ately result.

One termination methodis to have two screwterminals on the same

metal terminal

plate with theplate providing continuity between thescrews. See the illustration at the bot-tom of Figure 1. Thus the in wire wilconnect to one screw and the out wireto the second. Pressure plate terminalsare also widely used. Two wire ends arestripped and inserted under a pressureplate. A screw holds the plate downand maintains continuity between thewires. See Figure 2 for a description othe proper and improper terminationswith this type of terminal.

Another method of termination is withfour (4) pigtail connections, two forthe in wiring and two for the outwiring. See additional illustrations inFigure 2 for both improper and propermethods of connecting the pigtailsAn X shows the unsupervised wirewhich, if cut, will remain undetected.

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The ABCs of Fire Alarm Systems Part V . . . Continued from page 47Wiring to initiating devices in a conventional system ornotication appliances in addressable or conventional sys-tems must be made in an in and out fashion. Branchingor T-tapping is not permitted in these circuits. Again, thereason for this is that the current must ow in and out of eachdevice and nally through the end of line device so supervi-sion is maintained. Therefore, removal of a device from the

circuit or a break in the wiring will interrupt the supervisorycurrent and create a trouble condition. If a T-tap is used,a break in the T-tap branch will go undetected, since thesupervisory current will not be interrupted. Figure 2 alsoshows both proper and improper methods of connection.An X indicates a break that will go undetected.

Note that T-tapping is permitted in an addressable system,since the microprocessor polls all addressable devices andwill promptly detect a missing device.

A third method of wiring is commonly used with plug-instyle two-wire conventional smoke detectors. One wire goesin and out of one base terminal, usually a pressure plate type

of terminal. The other wire connects to a second terminal inthe base and exits from a third. The detector has a built-injumper that maintains contact between the second and thirdterminals, so if the detector is unplugged, it will cause a breakin the wiring resulting in a trouble signal.

The type of wire used for eld wiring should conform to thecodes in effect in the area. These codes are almost alwaysbased on Article 760 of the National Electrical Code, NFPA70, but some states make additional requirements. One statenot only species the acceptable types of wire, but also speci-es the insulation color, with DC power, initiating circuitwiring, initiating circuit return (Class A) wiring, noticationappliance circuits, etc. all having different insulation color

requirements! The prudent thing to do is to consult withthe Authority Having Jurisdiction, such as wiring inspector,re marshal, etc.

Until recently, solid or bunch-tinned stranded wire, 18 gaugeminimum, UL Listed for re alarm use, were the only typesof wire acceptable for re alarm. The reasoning behind thisrequirement was that solid or bunch-tinned stranded wirewould be most likely to break cleanly, giving an instanttrouble indication. If a stranded cable were to be damaged,leaving only one strand intact, the one strand would conductsupervisory current and maintain normal operation. Duringalarm, a notication appliance circuit could draw enoughcurrent to burn out the single strand, with a resultant failure

at the most critical time. Now the NEC contains exceptionsallowing stranded wire under certain circumstances. Inaddition, communication cable is also allowed in certaininstances.

Power limited and non-power limited wiring also comesinto account. There is no hard and fast simple rule aboutwhat types of circuits are power limited. The only way aninstaller can make this determination is that power limitedand non-power limited designations are printed by themanufacturer on the control panel door label or on the ter-minals themselves. A typical label might state: All circuitsare power limited with the exception of the AC input, battery

and city box connection.

Again, consult the local Authority Having Jurisdiction aboutthe wire hierarchy chart in the NEC, if your State Code isbased on the NEC.

Improper Termination Proper Termination

Figure 1

Figure 2

Fire AlarmControl Panel

Fire AlarmControl Panel

End of LineDevice

End of LineDevice

Smoke DetectorSmoke Detector

Smoke DetectorSmoke Detector

Pigtail ConnectionsCorrect Wiring Method Pigtail ConnectionsIncorrect Wiring Method

Correct Wiring Method

Incorrect Wiring Method