smoke detector basics

[oldchachie]

I live in superior wi. Im installing an elk m1 system. Im trying to figure out what smoe detectors to buy... Theres so many choices... 2 wire 4wire low voltage, 120v 3 wire ones... Can anyone point me to some basic info on these as two what the different types do, and particularly what the laws are about using the various types... By whar im guessing so far i can use the low voltage 4 wire type... Just not sure. Thanks!

 

[knowinnothin]

First stop for information would be electrical code for your area, where I'm located electrical code requires 120v interconnected in each bedroom plus hallway. Utility room requires co2 if gas service is present, heat detector in garage, etc. Different panels have different capacities for 2-wire/4-wire smokes, I'm using HAI and have no clue about elk. Your manual would tell you how many smokes your system supports for 2-wire and 4-wire. I'm sure a few other members with more knowledge will chime in sooner or later but the above info should point you in the right direction.

Good Luck

 

[oldchachie]

I found that wisconsin requires "Except for dwellings with no electrical service, smoke detectors required by this section shall be continuously powered by the house electrical service, and shall be interconnected so that activation of one detector will cause activation of all detectors". I'm not sure if this means they have to be powered by AC or if it si ok to step that AC down and transform it into DC then power smokes. Any comments?

 

[gatchel]

Interpretation and the AHJ are two key words here.

For example, 4 wire (low voltage) smokes that are powered from an alarm power supply is continuously powered from a 120v source, with battery backup even...

4 wires smokes that are daisy chained and whose power is fed through a reversing relay, will all sound at the same time if they have built in sounders. System sensor 4WTA-B would be an example of such a device.


One might interpret the code differently than another. As said in post 2, speak to your AHJ for the final word on what you can do. If he/she are intelligent and aren't on a power trip you will probably be fine with low voltage smokes. Ask first. Don't take my word for it.

 

[apostolakisl]

My 2 cents.

I have Elk m1g.

I use the GE 4 wire smoke detectors plus a reversing relay (449cste). It works very well and is not expensive. GE has units with built in eol relay for your last unit on the daisy chain or you can use that model for all of the units which will trip a trouble code if they fail self diagnostics.

You should check with your inspector to make sure that they don't require 120v models. If you get 120v models it gets fuzzy about connecting them to the Elk as far as code. It's pretty stupid if you ask me. The 12v models hooked up to Elk are UL listed, attractive, effective, and continue to work during a power failure.

2 wire smokes can be used with Elk. If so, you must use only the models exactly spec'd by Elk. It is written on the Elk itself.

4 -wire smokes don't require anything special except for using 4 wires instead of 2. From the standpoint of Elk, 4 wire smokes can be plugged into any zone you like and configured lots of different ways. 4 wire detectors can each be on their own zone or you can daisy chain them together in groups or just daisy chain the whole lot onto 1 zone. 2-wire model must be daizy chained all together to zone 16.

I should mention that you can use 2 wire detectors in different ways than I have specified, but it requires the use of adapters and I can't fathom the point in doing that.

When doing the wiring, you need to decide how you want things zoned. If you plan on putting all of your detectors on 1 zone, then daisy chain the wire from location to location. If you plan on using 4 wired detectors, they can be daisy chained or each home runned. If you home run them, then you will be forced to put them on their own zones (unless you home run 8 wires which allows you to go either way but would waste a lot of wire).

Edit: Regarding heat only detectors, these are "passive" detectors, meaning that they require no power. They are 2 wire devices that can be used with either system but can not be daisy chained into 2 wire systems (they go on their own zone). They can be daisy chained with 4 wire systems but you only use the 2 signal wires (not power wires). When it gets too hot, there is a conductive material that "melts" and shorts the contacts. Once "melted" it is a-gonner. They also do rate of rise but the units will self reset after a rate of rise trip provided it never gets hot enough to trip the max temp sensor.

 

[Del91574]

Without going into specifics, 2 wire offers the simplest wiring and less hardware than a comprable 4 wire circuit. If you wire a daisy chained 4 conductor, you have multiple options of what you can do, however you do need to pay attention to a reversing relay/polarity and heat detectors and where power is pulled from.

In 9/10 installations, the benefits of having each smoke on it's own zone or even separating a house into multiple zones is generally somewhat of a moot point and questionable benefit, which complicates wiring and complexity to get it working right for a tandem ring/reset/power supervisiory. While it's a "nice" on paper item, most houses would have 7-8 smokes max to meet present code, assuming 3 stories and 3-4 BR. If you have a large install, honestly, I believe it's better to move to addressable systems and then work on integration rather than analog smokes.

The big item that was mentioned is to ask your AHJ what their expectations are for an installation and what they will allow/pass, as they're the ones that make the rules, everything else is conjecture.

 

[apostolakisl]

Perhaps you will find the following explanation helpful.

All smoke detectors are powered devices.
- 4 wire devices use 2 of those wires for power and 2 for alarm signal. The 2 alarm signal wires are a normally open circuit that can be wired to pretty much any alarm panel at any zone in a very generic fashion. You would also use a resistor at the end of signal wire line so that a small amount of current "leaks" through it which in turn drops down the voltage at the panel. The lower voltage allows the panel to supervise (monitor) the condition of the wires since a broken wire would no longer "leak" out some of the voltage. When in alarm, the wires are shorted and the voltage at the panel drops to 0. A main point with 4 wire is that you must also supervise your power wires with an eol relay. This supervises that power is making it to the end of the line (and presumably then to everything before it). When power is lost to the relay, it opens the signal wire circuit which in turns takes the eol resistor out of the loop just the same as a broken wire would and the panel sees the voltage go up and reports trouble.
- 2 wire devices put both power and signal on the same set of wires. This makes things more complex from the standpoint of the eletronic protocols of the devices and these protocols are not universal. So you have to use the detectors that are specifically matched to the alarm panel and can not exceed the preset max limit. With the elk, all of those units must be daisy chained onto zone 16 and the jumper must be set to 2 wire mode. The upside to this is that you can use cheaper double stranded wire. You also only have 2 wires to hook up at the devices and you do not need an eol relay since there are no separate power wires to supervise. You will still need a resistor at the end of line. The downside is everthing goes together on zone 16.

2 wire and 4 wire detectors have similar optional features. Things like sounders, thermal detector, and relays that close when alarming (not the same as eol relay). Units with sounders also may have a feature of sounding when power polarity is reversed. The code is to have sounders on all units and to have all units sounding when any one of them detects smoke/heat. To do this, you will need to purchase a separate relay that does that polarity swap for you when the alarm goes off.

 

[Del91574]

Of note, which Lou didn't touch on, is while 4 wire units are "universal" in nature, mixing manufacturers on the same loop or even in the same install isn't recommended, as some manufacturer's devices operate differently upon alarm condition and reset and don't play nice on certain panels. The big ones here are DSC and Bosch/DS smokes operate differently on the powered side of the detector so you can't mix those with say, a GE or System Sensor smoke.

A separate relay for tandem ring may or may not be needed by your particular manufacturer, and if your install has additional outputs already installed, you may not need a separate reversing relay, however most opt to install one to simplify the wiring and programming.

 

[gatchel]

Also mixing different device types on the same zone is a no no also, right?( For example using smokes with a standard heat detector on the same zone...)

 

[apostolakisl]

Also mixing different device types on the same zone is a no no also, right?( For example using smokes with a standard heat detector on the same zone...)

Certainly not with 2 wire detectors.

With 4 wire detectors, the 2 signal wires are a normally open circuit which works no different than any other normally open zone. Placing a heat detector which is a passive device using only the signal wires (no power) works and does not damage anything. Some would say you should not do this, but those would be esoteric arguments in my opinion.

 

[gatchel]

I wasn't referring to different detector types, different device types ie heat only and smoke devices. I guess it a more of a "best practice" thing.

 

[apostolakisl]

I wasn't referring to different detector types, different device types ie heat only and smoke devices. I guess it a more of a "best practice" thing.

Right, you can mix passive heat detectors with active 4 wire smoke detectors since the passive devices only use the 2 signal wires.

As Dell mentioned, mixing different brands of 4 wire detectors may or may not be a problem. This relates to the way the power leads work, not the signal leads.

2 wire detectors should never be mixed in any way unless specifically indicated by the manufacturer.

 

[gatorhwk]

I'm in Tampa, FL. My builder's electrician just told me their smokes and co2 detectors need to be 120V per code. He said I could run LV to additional smokes for my Omni 2 if I wanted to. I guess I'll have to take this up with the city if I really want to connect my smokes to the security system. Anyone have any takes as to why I MUST connect these to my Omni 2? I already explained the Omni 2 is powered by HV and having a battery backup takes it another step beyond straight HV. Just wondering if it's worth possible delays in construction.

 

[oldchachie]

Not sure if I have to use the 120v ones or not yet, been plannin on askin the inspector. I was also thinking, I want a circuit for the house and for each garage, and I'm not sure if I care which smoke is going off within each of those, so long as I know which building it is... so I'm thinkin I might just use a relay off of the 120v interconnect line to trigger an input to the ELK... but I'm not going to have any time to work on it this weekend anyway, so waiting till next weekend probably isn't a problem.

 

[Del91574]

Right, you can mix passive heat detectors with active 4 wire smoke detectors since the passive devices only use the 2 signal wires.
As Dell mentioned, mixing different brands of 4 wire detectors may or may not be a problem. This relates to the way the power leads work, not the signal leads.
2 wire detectors should never be mixed in any way unless specifically indicated by the manufacturer.

Not entirely true. It is not recommended to install heat detectors on a 2 wire loop with a reversing relay, as when the polarity is reversed, the short is maintained, which can damage the panel/power supply the reversed power is drawn off of. Heat detectors should be separated from the loop that has a reversing relay installed.

As far as the post above me, by saying "garage" I hear it as uninhabitable space as specified by code, which would preclude the installation of smoke detectors. If your garage has sleeping areas, that's a different item altogether.