# hardwired smokes vs. system smokes



## cheyer (May 13, 2010)

Do you allow system smoke detectors (24v) tied to a small panel vs. harwired smoke alarms with battery back-up for R-3's?

It appears our fire code does have an exception that would allow that....but I'm wondering if it is as reliable as the hardwired option.

Thanks.


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## Mule (May 13, 2010)

No. The IRC requires the smokes to receive their power from a commercial source.

R313.3 Power source. In new construction, the required

smoke alarms shall receive their primary power from the building

wiring when such wiring is served from a commercial

source, and when primary power is interrupted, shall receive

power from a battery.Wiring shall be permanent and without a

disconnecting switch other than those required for overcurrent

protection.


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## bgingras (May 13, 2010)

But, where does your code state that the power must be 120V? I see that as allowing a transformer supplying power from the primary power of the building. How does one address the system with over 12 smokes, when a lot of these systems are low voltage?


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## FM William Burns (May 13, 2010)

C,



Our jurisdiction allows systems via ordinance but when this option is used it must be installed in accordance with NFPA 72, 2007 Chapter 11 Single- and Multiple-Station Alarms and Household Fire Alarm Systems.  Power supply must be in accordance with [11.6.2]



Since they are installed in accordance with 72 (when they choose this option) they are supervised household fire alarm systems and can go beyond the interconnection limits and have been extremely reliable in our jurisdictional history where installed.


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## cda (May 13, 2010)

http://www.inspectpa.com/phpbb/showthread.php?1442-Residential-smoke-detection-systems

yes but they have to have either a mini horn in each bedroom or smoke detectors that sound upon alarm


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## FM William Burns (May 14, 2010)

Yep, part of the notification reference in the document's chapter.


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## Mule (May 14, 2010)

bgingras said:
			
		

> But, where does your code state that the power must be 120V? I see that as allowing a transformer supplying power from the primary power of the building. How does one address the system with over 12 smokes, when a lot of these systems are low voltage?





			
				Mule said:
			
		

> R313.3 Power source. In new construction, the requiredsmoke alarms shall receive their primary power from the building
> 
> wiring when such wiring is served from a commercial
> 
> ...


*the required smoke alarms shall receive their primary power from the building wiring *

I think the key word is "primary". Primary power from the building wiring. If you have a panel with 24 volts, the SD are receiving their power from a different source than building wiring.



			
				bgingras said:
			
		

> How does one address the system with over 12 smokes, when a lot of these systems are low voltage?


If the system complies with NFPA 72,

Household fire alarm systems installed in accordance with

NFPA 72 that include smoke alarms, or a combination of

smoke detector and audible notification device installed as

required by this section for smoke alarms, shall be permitted.

If installed per NFPA 72...all is well!


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## TimNY (May 14, 2010)

I would interpret that as "primary power" versus "backup power". Consequently I would say a low voltage smoke alarm receives it's primary power from the building wiring.

But don't fret!  I agree LV is not prescriptively allowed.

I personally would refer to the definition of smoke alarm: "An assembly incorporating the detector, *control equipment* and *alarm sounding device** in one unit* that is operated from a power supply *either in the unit of obtained at the point of installation*"

A low voltage smoke detecor does not incorporate the control equipment, nor do they obtain power at the point of installation.  They may or may not incorporate a sounder.

Strictly an approved alternate method.


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