Hardwired smoke detectors 120volts, battery backup per device?

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grasfulls

Senior Member
I am sure this has been answered already, someplace, but all I have found is the verbiage "hardwried" with battery backup. I cannot find where it must be 120 volts hardwired. Can anyone please direct me there? Also, does battery backup mean each invidual detector must have a battery or can it be one large battery for the entiree system, like a UPS that will run them for a week?
 

Dennis Alwon

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Location
Chapel Hill, NC
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Electrical Contractor
I don't know if calif. is different but hard wired can be 12V systems anywhere in NC and I believe most of the country. Many systems have the detectors as part of the security
 

Dennis Alwon

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Location
Chapel Hill, NC
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Electrical Contractor
Here is all it states. It does not state the source must be 120V

4603.7.3 Power source. Single-station smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system.
Smoke alarms shall emit a signal when the batteries are low.Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
 

grasfulls

Senior Member
hardwire=120vac

hardwire=120vac

Yes, hardwired does not mean 120v. And yes it could be a UPS system.
So to hardwire my 24VDC doorbell I should have run 120 to it??
I believe hardwired merely means it cannot be a plug in, but this to is not true for most smoke detectors as they use a plug adapter to "hardwire" it to the incoming lines. However, I would like to see where the term "hardwired" is formally defined as 120 volt wiring.

Thanks!
gare
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
So to hardwire my 24VDC doorbell I should have run 120 to it??
I believe hardwired merely means it cannot be a plug in, but this to is not true for most smoke detectors as they use a plug adapter to "hardwire" it to the incoming lines. However, I would like to see where the term "hardwired" is formally defined as 120 volt wiring.

Thanks!
gare
The words 'hardwire and hardwired' are not in the rule Dennis posted. I think the word is a form of electrical slang.

Edit to add: Neither of the words are in the NEC, either. So I guess you should ask the person using the term what they mean by it. I don't see how a formal definition of an unused word is needed.
 
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grasfulls

Senior Member
define hardwired

define hardwired

The words 'hardwire and hardwired' are not in the rule Dennis posted. I think the word is a form of electrical slang.

Edit to add: Neither of the words are in the NEC, either. So I guess you should ask the person using the term what they mean by it. I don't see how a formal definition of an unused word is needed.
Not used in the NEC, but there are building codes that stipulate hardwired battery backup, the alarm people I have talked to say that hardwired has nothing to do with voltage...hence my question in here.

thanks!
 

grasfulls

Senior Member
commercial power

commercial power

Here is all it states. It does not state the source must be 120V
Single-station smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source
Interesting rule with respect to "from commercial source". Does this mean the utility transformer? If a building has a 480 or 12kv primary and we step it down as an end-user, is that no longer "commercial". If we can do that, then I think we can put in a transformer from 120 to 24 volts (or whatever) and make use of it for low voltage devices. yes?
 
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K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Interesting rule with respect to "from commercial source". Does this mean the utility transformer? If a building has a 480 or 12kv primary and we step it down as an end-user, is that no longer "commercial". If we can do that, then I think we can put in a transformer from 120 to 24 volts (or whatever) and make use of it for low voltage devices. yes?
I have never seen a smoke alarm powered from an external source that wasn't 120 VAC. If they do exist, I'll bet they are more expensive than the garden variety 120 volt alarms, so I don't see any advantage to using a different voltage.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
It's not an NEC issue. Local code here requires hardwired 120v with battery backup interconnected smokes with CO detectors even if there are LV smokes all over the place connected to a security system. I believe the only exception is if there is a listed fire system.

-Hal
 

grasfulls

Senior Member
no advantage

no advantage

I have never seen a smoke alarm powered from an external source that wasn't 120 VAC. If they do exist, I'll bet they are more expensive than the garden variety 120 volt alarms, so I don't see any advantage to using a different voltage.
Alarm companies installing residential monitored systems are almost always low voltage. I always exclude smokes and carbons if a monitored or addressable system is going in. All the devices are then using class 2 wiring which is much easier to install and mess with and I do not have to be concerned with what they are doing. Twice lately I have been asked to install a parallel system because the alarm company said "it was not in our contract". They have the ability to install common annunciation devices with battery back-up, but they need to be told - not my fault, this is a GC or homeowner issue at that stage.

The GC was on me for not "knowing" there had to be a 120volt system....that is what spawned all of this, I have never seen a 120 volt requirement.

gare
 
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gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
IBC

IBC

Alarm companies installing residential monitored systems are almost always low voltage. I always exclude smokes and carbons if a monitored or addressable system is going in. All the devices are then using class 2 wiring which is much easier to install and mess with and I do not have to be concerned with what they are doing. Twice lately I have been asked to install a parallel system because the alarm company said "it was not in our contract". They have the ability to install common annunciation devices with battery back-up, but they need to be told - not my fault, this is a GC or homeowner issue at that stage.

The GC was on me for not "knowing" there had to be a 120volt system....that is what spawned all of this, I have never seen a 120 volt requirement.

gare
Any jurisdiction that has adopted some version of the International Building Code will likely have this requirement for new construction. It's that way in the entire state of New Jersey
 

grasfulls

Senior Member
Local code requires

Local code requires

It's not an NEC issue. Local code here requires hardwired 120v with battery backup interconnected smokes with CO detectors even if there are LV smokes all over the place connected to a security system. I believe the only exception is if there is a listed fire system.

-Hal
Thanks Hal, makes sense. what city and where might I read the code?
gare
 

cowboyjwc

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Location
Simi Valley, CA
So to hardwire my 24VDC doorbell I should have run 120 to it??
I believe hardwired merely means it cannot be a plug in, but this to is not true for most smoke detectors as they use a plug adapter to "hardwire" it to the incoming lines. However, I would like to see where the term "hardwired" is formally defined as 120 volt wiring.

Thanks!
gare
So where did you get that from my answer? I said that hard wired does not always mean 120v, it could be a 24v system with battery back up, and battery back up could come from a UPS system. No one stated whether it was residential or commercial either.
 

grasfulls

Senior Member
So where did you get that from my answer? I said that hard wired does not always mean 120v, it could be a 24v system with battery back up, and battery back up could come from a UPS system. No one stated whether it was residential or commercial either.
I did not see the NOT..sorry about the confusion, that is the state I live in - the state of confusion, city of blindness.
 

iwire

Moderator
Staff member
Location
Massachusetts
I will be surprised if hard wired "smoke alarms" are available in anything other than 120 volt.

The devices that run from 12 or 24 volts are usally smoke dectectors and in many places the code requires smoke alarms, not smoke detectors.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I will be surprised if hard wired "smoke alarms" are available in anything other than 120 volt.

The devices that run from 12 or 24 volts are usally smoke dectectors and in many places the code requires smoke alarms, not smoke detectors.
Bingo!! :thumbsup:
 

brycenesbitt

Senior Member
Location
United States
Alternatives to 120V

Alternatives to 120V

I have never seen a smoke alarm powered from an external source that wasn't 120 VAC. If they do exist, I'll bet they are more expensive than the garden variety 120 volt alarms, so I don't see any advantage to using a different voltage.
Those are sometimes called "direct wire" smoke detectors, for example the System Sensor Model 2012H Photoelectric. You can wire it up with easy to run four conductor 18 gauge wire! A big advantage is no future semi-electrician will mistake your 14 gauge smoke detector run for a good place to add a 15 amp outlet. And you can more easily branch off an existing 20 amp circuit for the detectors.

The 2012H is a smoke alarm, not just a detector. "Built-in 85dB electronic horn with temporal (3) tone NFPA72 required audible emergency evacuation signal". Check for battery backup options.
 
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