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Old 07-27-2010, 07:10 PM   #1
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What's the minimum gauge wire required to run 9volts 50 feet?


Thread Summary: If your smoke detectors are on different circuits, the question was raised if you could run a separate 18 gauge wire between them to make them an interconnected system. The answer is a definitive "no", as Kiddie smoke detectors, at least, use the neutral for both AC and interconnectivity's 9 volts, so they must be on the same circuit.

What am I doing? Smoke detector interconnectivity wiring.

Yup, I know they're all supposed to be on the same circuit and you use the red wire for interconnectivity. I'd love to be able to do that, but the house was built in the 80s.

So what am I doing? I'm running a single wire from all the hardwire smoke detectors that are already in place. This wire will be cold 99.9% of the time, and when it isn't, it will have 9 volts (At what amperage, I do not know) running to tell the other alarms to go off. At the absolute longest possible run I could make in the house it would stretch about 50 feet. (Townhouse...and I'm not putting a smoke detector on the basement floor)

So, I could just buy a single 14awg cable and run that, but I figure at 9 volts it probably doesn't need that...and a thinner cable will be easier to run. I'm thinking hardwired doorbell gauge wire. 16 or something. Anyone know if that's legit?

I put a question into Kiddie about it, but who knows how long they'll take to respond. Was curious if anyone here had any ideas.

Thanks!

Last edited by Fox; 07-29-2010 at 03:32 PM. Reason: Added summary
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Old 07-27-2010, 07:34 PM   #2
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9 v battery puts out 10 mA or less?

5% wiring drop for 10 mA = 0.05(9)/0.01 = 45 ohms max wiring resistance.

50' of #30 two conductor gives 10 ohms but it is not mechanically strong.
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Old 07-27-2010, 07:53 PM   #3
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So what is ONE wire going to do for you?
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Old 07-27-2010, 08:44 PM   #4
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Quote:
Originally Posted by Speedy Petey View Post
So what is ONE wire going to do for you?
I think he is powering the SD from a local circuit and the single conductor is for the common interconnection to activate the others.
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Old 07-27-2010, 10:50 PM   #5
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Quote:
Originally Posted by nap View Post
I think he is powering the SD from a local circuit and the single conductor is for the common interconnection to activate the others.
Exactly what he said.

Quote:
Originally Posted by Yoyizit View Post
9 v battery puts out 10 mA or less?

5% wiring drop for 10 mA = 0.05(9)/0.01 = 45 ohms max wiring resistance.

50' of #30 two conductor gives 10 ohms but it is not mechanically strong.
Yoyizit, thank you...but I'm afraid I've no idea what #30 two conductor is. Is that 30 gauge cable? Does two conductor mean two 30awg cables?

Good point about 'mechanical strength' by the way. While I'll be pulling with fish tape and thread, I should consider that some minimum wiring may snap within the sheath, unbeknown to myself. I'll ramp it up a little in strength, and then run a test of all the alarms. Wouldn't be worth a damn if I have a fire in the basement and don't hear it sleeping upstairs, eh?

Last edited by Fox; 07-27-2010 at 10:57 PM.
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Old 07-27-2010, 10:59 PM   #6
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How will you make the other detectors go off? Are you good at electronics and able to figure out what part of the circuit is the trigger? Just curious. I've always thought of how cool it would be to link fire detectors so if one goes off, they all go off, like in commercial settings. (big bucks for systems like this). Of course some kind of indication of which detector triggered would be nice too.

Another fun thing to setup would be some kind of email notification, so if you are at work you know a detector went off at home, and it's time to take an emergency break. Wonder if there's affordable systems out there that have features like this.
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Old 07-27-2010, 11:18 PM   #7
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Red Squirrel, you're way behind the times

$12 will buy you an interconnectable smoke detector, which is required in most municipalities.
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Old 07-27-2010, 11:29 PM   #8
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All the hardwired detectors I've seen in Home Depot have white and black wires for AC power, but a spare yellow wire is designed in many brands for interconnectivity. I've only researched Kiddie smoke alarms, but they use the same signaling technique, so they all work together. They also have a list on their website of models of other brands they've tested that work.

Basically if one alarm is set off (not just using the test button) it will set off all the other alarms. The alarm that sensed the fire will have a different light blink code than the rest, but the basic smoke detectors don't report the location of the fire.

I believe what you're referring to is a fire alarm system. Those are commercial, computer controlled and far more sophisticated. Technically if you brought all the smoke detectors to a central location in the household and simply wired up a box that monitored the lines for low voltage it wouldn't take much coding to have a server read these signals from a USB port and respond appropriately. Not only would all the alarms go off as long as the signal was passed to the others, but the server could easily send to email, as well as SMS (text messaging) and other forms of communication, not to mention calling the local fire department with a recorded message.

Keep in mind that battery operated smoke detectors (without wireless capabilities: e.g. HomeHero, etc) usually won't have an interconnectivity option.
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Old 07-28-2010, 12:11 AM   #9
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I know you mention townhouse if that is in the conduit the minuim conductor size is 2.5 mm˛ {14 AWG }

Otherwise a 2.5mm˛Tripler cable aka 14-3 NM will work just fine with this useage.

The black is hot feed while the White is netural and some brand will have yellow and some will have red lead that is interconnection lead { make sure you don't get 120 volt on this one otherwise you will make magic smoke of it }

It is not too uncommon for me to run over 100 meter of smoke detector cable for interconnection devices all I have to just watch the numbers of units to be on the same time otherwise it will not sound off at all.


Merci.
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Old 07-28-2010, 08:38 AM   #10
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Kidde IIRC make a hard-wired smoke that communicates wirelessly with others in the house. You install one master unit and all the rest are slaved to the master.
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Old 07-28-2010, 09:42 AM   #11
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So, Kiddie responds pretty damn fast it seems, but I get this disclaimer at the bottom of the email:
Quote:
The information contained in this message or any of its attachments may be privileged and confidential and intended for the exclusive use of the addressee. Any views or opinions expressed in this e-mail are those of the individual and not necessarily of Kidde Safety/UTC Fire & Safety. If you are not the intended recipient, any disclosure, reproduction, distribution or other dissemination or use of this communications is strictly prohibited.
Hmm, well, I'll include the public stuff in the email:

Quote:
Good Afternoon

In response to your email, in order to interconnect the alarms and to be up to code, you have to use standard electrical wring and all three wires have to be in the same jacket, like Romex 12-3 or 18-3 wire. To interconnect, all of the alarms have to be on the same circuit, the same hot wire, same neutral and same interconnect wire.

You had to have use standard UL-listed electrical wire, 18 gauge 18-3 wire or larger, for the circuit

All of the alarms have to be on the same circuit

There had to be three wires, a black HOT, a white NEUTRAL, and a red INTERCONNECT that has no power going over it. You can NOT use the ground wire as an interconnect wire

There has to be 110-125 volts between the black and white, and there has to be NO POWER between the red and white. If there is ANY power going over the red wire, this will damage the interconnect circuits of the alarms.

If the alarms are not all on the same circuit, they will not interconnect and it can damage them to run a third wire from alarm to alarm to alarm but not have them on the same circuit. When one alarm goes off, it sends an 8-10 DC volt modulated signal between the red interconnect and white neutral wire- the white neutral wire does double duty for both the 120 VAC circuit and the DC volt interconnection circuit.
Seems a standard form letter to a generic question about interconnectivity, but I got the 18 gauge answer I was looking for. It may not be up to code, but it'll be a lot safer than it is now.

Jim, I considered the wireless, but I'd be throwing away $80 worth of existing smoke detectors that route, and would wind up spending more for wireless models when I was installing a lot on the top floor, which will all have easy attic access. I was banking on saving cash that way, unless they've some equally priced, wireless, photo-electrical smoke detectors I didn't see. Honestly they've so many that aren't always clear about their features it's a bit overwhelming.

I'm still curious what Yoyizit was talking about.
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Old 07-28-2010, 09:52 AM   #12
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If you check I beleive that the wireless will also work with the wired ones. This way you could just add to wirelsss to the ones that will be a pain to wire.

Lots of people wonder about the comments of a certain few. Some seem to drift into a tangent. Don't loose any sleep over it.
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Old 07-28-2010, 09:55 AM   #13
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Quote:
Seems a standard form letter to a generic question about interconnectivity, but I got the 18 gauge answer I was looking for. It may not be up to code, but it'll be a lot safer than it is now.
safer? they specifically state you cannot do what you are proposing. I suspect if you use a circuit from an opposing leg in the panel, you might have an over voltage problem in the signaling circuit and that is what would cause the damage.


Quote:
I'm still curious what Yoyizit was talking about.
I suspect everybody here has said that at one time or another.
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Old 07-28-2010, 10:06 AM   #14
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Quote:
Originally Posted by nap View Post
I suspect everybody here has said that at one time or another.
Yup, count me in, and I'm brand new here!
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Old 07-28-2010, 10:07 AM   #15
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So as long as you have all the detectors on the same circuit you could run a wire
....but does not meet code...IE wires not all run together
I guess all interconnected is better then stand alone

I've been "lucky" in that both houses did not have any hard wired
...actually this house did have one on the 2nd floor
So I have run 14-3 & added all detectors
I also bought one for each floor that was a combo SD & CO
--it talks - tells you Fire....or CO detected
also all Kiddie alarms
2nd floor near stairs I bought one with a built in light that goes on



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