Wiring for 2+ smoke detectors for Elk M1G

I'm pulling my last wires before getting ready to hang the new drywall, and making my final "wish list" for future projects. I only HAVE to have a single smoke detector, but I wouldn't mind adding a few more if it wouldn't end up being enormously more expensive.

I know that it's trivially easy to connect a single 2-wire or 4-wire 24v smoke detector to the Elk M1G... but what does adding #2 and beyond entail? I've kind of gotten the impression that, among other things, you have to ALSO add expensive relays that cost more than the detectors themselves, but I'm not sure whether I was misunderstanding what I read, or whether the relay-requirement only applies to 2-wire or 4-wire alarms.

Likewise, if 110vac is readily-available from a nearby junction box, would 110vac detectors be easier/cheaper/better, or would I just be adding new, expensive headaches to the equation?

Do I just need to run a cat5 cable to each future/potential smoke detector location (terminating them all in the same panel), or does each detector need TWO cat5 cables?

Do 24v smoke detectors normally get screwed to the wall over a hole from which the cat5 pokes out? Or are they normally/always installed over octagon boxes, pancake boxes, or something else?

For what it's worth, the area we're talking about here is the second floor of my house. It's a townhouse with front and rear bedrooms, and bathroom+hall+stairs in the middle. The current (battery-powered) smoke detector is in that hall, and that's basically where a single new detector wired to the M1G would go as well. The proposed locations for two additional detectors are the two bedrooms; each proposed additional smoke detector would be a whopping 15 feet or so away from the one in the hall -- we're not exactly talking about a large mansion here. Ergo, the reason why I could go along with spending an extra $35 or so per room to throw up a second and/or third one in the bedrooms if all I need is the cat5 and the detector, but why I'd seriously balk at spending way more than that just to add detectors #2 and #3 just a few feet away from detector #1 (for what it's worth, I don't smoke or use space heaters, which pretty much eliminates the 2 biggest causes of fires that start in bedrooms anyway).

miamicanes said:

I know that it's trivially easy to connect a single 2-wire or 4-wire 24v smoke detector to the Elk M1G... but what does adding #2 and beyond entail?

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Actually it's trivially easy to connect more than one smoke detector -- just parallel the power and zone lines (4-wire) out to each unit. Consider using 12V detectors because you can then power them directly from the M1. You just run a continuous pull of 4 wires to each detector location, from the M1 in a continuous string out to the last smoke detector.

You definitely should have an EOL relay (EOL=end of line) to "supervise" the power and zone lines (to be sure power is getting to all of the detectors, and that the zone line is intact). You only need one of these, and you should do this whether you have one or many smoke detectors. It is very cheap insurance against a failure of your fire zone. The EOL relay is located at the physical end of the cable run.

Potentially another kind of relay in your application is a power-reversing relay. This would apply if you choose to have "sounders" in one or more of the smoke detectors, and the reason for using it is to have more alarm sound in more locations in case of a fire. This relay is located at or near the M1 and is activated only when the fire zone is triggered by any one of the smoke detectors. What it does is reverse the power to all of the smoke detectors, which are designed and built specifically to sound off when their power supply is reversed. So the end result is that when one smoke detector is triggered, the fire zone is violated, the reversing relay is activated, the power supply to the detectors is reversed, and all of the smoke detectors sound off.

You probably have building code implications in what you are doing, for example with respect to your wiring, the number and location of your smoke detectors, and how loud the alarm signal needs to be. Others who have knowledge of these issues -- which is certainly not me -- will have to comment.

I agree with Lagerhead that you need to check with your local Authority Having Jurisdiction to see what their requirements are. Some localities will want you to use 110 V detectors wired on a dedicated circuit with a third wire so that they all sound if one goes into alarm. Others will allow the same but with low voltage detectors if they all have sounders and sound at the same time. Other localities may want something else. AHJ's are the final say in their area no matter what the NFPA etc says.

In this case its best to ask permission rather than forgiveness. To much of a risk of not getting a Certificate of Occupancy or having a problem on resale. And you dont want to have to rip out your sheetrock for this someday.

Well, in this case the code is largely irrelevant. It's an existing house, and as far as the 25 year old blueprints on file at City Hall show, there's only a single non-wired smoke detector (in 1982, the code apparently required at least one smoke detector, but didn't require that it actually be wired in). So I'm free to go for cost-efficiency and maximum bang-per-buck. Down here (South Florida), house fires not involving smoking in bed or marijuana use (nope), a wood roof (mine's concrete), a public housing project (nowhere near the 'hood), a meth lab (nope), or arson (yeah, after all the work I've done...) are almost unheard of.

Basically my goal is to keep the level of functionality I have now (at least one detector that's perfectly capable of running from its own battery and making its own noise), but add the Elk's monitoring/autodial capabilities & possibly a few more detectors if it's affordable. I don't want to have to bulletproof the system to commercial standards and have a scenario where the Elk M1 *itself*, and the wiring connecting them, are critical components that have to be perfect in order for them to work *at all*. Worst case, if the Elk is dead, the 12v is gone, and the wiring is cut/wrong, I want any detector that senses smoke to make lots of noise on its own, using its internal 9v backup battery, anyway.

As far as the relay for reversing power to the detectors... doesn't the M1 have a power lead for that specific purpose (constant power, but the M1 can cut power to it to silence a sounding alarm)? Also, don't some 4-wire detectors designed for the home/noncommercial market have EOL detection built in? (ie, flip a switch or add/remove a jumper to enable end-of-line monitoring)?

Also, how do 12v alarms (presumably 4-wire) handle alerts for low backup battery? Do they just act like normal battery-powered alarms, initially giving a chirp every 8-12 hours and slowly decreasing the time between them (since mfrs learned the hard way that if they make it TOO initially persistent & annoying, people will just get mad at 2am & rip the battery out altogether), or is there some signaling protocol that lets them notify the panel that the battery is low in a way that can be differentiated from a detected smoke event?

miamicanes said:

I don't want to have to bulletproof the system to commercial standards and have a scenario where the Elk M1 *itself*, and the wiring connecting them, are critical components that have to be perfect in order for them to work *at all*.

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But this is exactly why most of us have a solid system like the M1 in the first place. It is not that difficult to have a highly reliable, dependable installation. You only need to take steps to automatically *discover and notify* when something has gone less than "perfect."

miamicanes said:

Worst case, if the Elk is dead, the 12v is gone, and the wiring is cut/wrong, I want any detector that senses smoke to make lots of noise on its own, using its internal 9v backup battery, anyway.

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If the Elk is dead -- battery drained etc. -- you must be in the midst of some other real crisis and have bigger problems to worry about than your fire zone. If it makes you more comfortable, then have a few stand-alone battery-operated smoke detectors. For me, I depend entirely on the M1 and my smokes, and I think most people here would agree.

miamicanes said:

As far as the relay for reversing power to the detectors... doesn't the M1 have a power lead for that specific purpose (constant power, but the M1 can cut power to it to silence a sounding alarm)?

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The M1 SAUX terminal is specifically to power smoke detectors. It does have a function that cuts the power to reset the smoke detectors, but it does not provide for power reversal.

miamicanes said:

Also, don't some 4-wire detectors designed for the home/noncommercial market have EOL detection built in? (ie, flip a switch or add/remove a jumper to enable end-of-line monitoring)?

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I'm sure I don't know the answer to this one. I have a bunch of System Sensor smoke detectors (old and new generation mixed) with a separate EOL relay located in the box of the last smoke detector.

miamicanes said:

Also, how do 12v alarms (presumably 4-wire) handle alerts for low backup battery?

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You are describing powered smoke detectors that also have a replaceable battery? I was not aware of these.

It is possible that your renovation is extensive enough to require you to meet the latest code. Maybe not.

Good luck with your install whatever you decide to do.