2-wire or 4-wire smokes? Which is better?

[benze]

Hi,

So I was all set to order a bunch of 4 wire System Sensor i3 smoke detectors to add to my M1G panel, and called up System Sensor just to get a couple of small questions clarified before I did. However, while speaking with them, they gave me more questions to think about. So now, am somewhat confused and am looking for feedback from others.

The M1G can support either a single 2-wire zone with the i3 devices or as many 4-wire zones as needed. Although the 4 wires smokes give you more flexibility from that perspective (ie: each floor can have its own zone), each zone would require its own EOL relay and hence makes installation / wiring a little more complex (ex: need to find somewhere to hide the relay if mounting directly to drywall without an electrical box).

On the other hand, the 2 wire smokes can be connected to a Maintenance Module (2W-MOD2) which will indicate if the smokes are having any trouble by signaling a separate zone. The Maintenance Module doesn't exist for the 4 wire smokes.


And finally, System Sensor mentioned yet another type of 4-wire detector that is non-latching, so doesn't need to be reset once the smoke clears (2012JA).


So the question becomes which is the best solution? I'm a little uneasy with the non-latching sensors, however, the reality is if the system is supervised by the central, they'll still get notified, and it makes it less hassle for me to reset the detectors if the smoke has dissipated already (ex: burnt toast, etc). And between the 2wire and the 4wire, I really have no idea which is better, if that can even be asked. Is there any advantage to going 2-wire instead of 4?

Thanks for any advice / insight!

Eric

 

[TXFlatLander]

I personally would go with 4 wires each on their own zone so you know exactly where the fire is and can announce it. The System Sensor 4-wire i3 series has a remote tester that you can use (model SENS-RDR) to test each sensor without using a multimeter.

Edit: I have model 4WTAB

 

[icellama21]

Don't worry about the relay. Just poke a hole in the drywall to tuck it behind. Make sure to plug the hole with something relatively air-tight(wad of insulation can work well), and use the surface gasket provided with the detector. Air leaks can lead to false alarms or missed alarms.

 

[Sandpiper]

Don't worry about the relay. Just poke a hole in the drywall to tuck it behind. Make sure to plug the hole with something relatively air-tight(wad of insulation can work well), and use the surface gasket provided with the detector. Air leaks can lead to false alarms or missed alarms.

I had a false alarm alarm one time caused by a small bug of some type. After the fire department left, I took the smoke unit apart and found the small critter crawling around near the photoelectric sensor. After that, I completely sealed the box with a generous dose of caulk.

Another comment/question.....do any 2 wire smokes have local sounders? Also, if they do, can you get them to sound all other smokes in the house? I know that some 4-wires can, but you have to use a reversing relay to make them work.

 

[gatchel]

I use the 4W-TAB models just because there is no issue with the number of devices per zone. I really don't care about the exact location of the fire or smoke because in a 2000 sq ft home you really don't have enough exits to be able to look at the nearest keypad and decide on an exit path. Once I am at the keypad, I am at the front door. I could find the smoke in about 10 seconds by just going from room to room. My wiring is daisy chained from he panel to the last detector with the supervision relay there. My sensors latch and have to be reset at the Keypad. That way if there is a problem with out a real problem I can troubleshoot it.

 

[Digger]

I would not recomend just poking a hole and have the EOL relay hanging in the wall or ceiling. While I know I have seen this so many times by some (not all) professional installers since they are apparently interested in getting in and then out of the install as fast as possible and as cheap as possible it is not good practice (those free or $99 installs only get you so much). An electrical box is less than a dollar for a plastic version. Granted it is more work.

My opinion (it is an opinion and I am not quoting code) is that at the very least at the last detector in each line use an electrical box to mount the detector and house the EOL Relay. Personally I would use an electrical box at each detector but I tend to be over cautious based on what I have seen and read over the years. Recent changes to UL864 Commercial Fire alarm Standard require that new EOL Relays have a means for mounting in a box (not just loose in a box). That will be in the residential standard shortly I am told.

Keep in mind that when you go to sell your house the home inspector might bust your chops on things like this or say to the potential buyer it looks like it was done right. That is secondary to the fact that you want your system to be reliable god forbid you need it.

Also do NOT use Cat 5/6 wire for fire devices. I have seen and heard of people doing this. Not only is it against code but the terminal blocks on most smoke detectors are not made for that small of a wire. Try and use 18 awg fire wire if you can.

The electrical code is not perfect and it is a PIA at times but the requirements are based on years of data of what went wrong and is an attempt to minimize that to protect lives and property.

BTW I am NOT a licensed installer but I do work with one at times when I am laid off etc. My main occupation is in compliance engineering for a mfg of alarm equipment. The guy I work with for installs makes a profit but he is not a "truck slammer" looking to make a dollar and get out. If he was I could not work with him.

 

[PaulD]

Another comment/question.....do any 2 wire smokes have local sounders? Also, if they do, can you get them to sound all other smokes in the house? I know that some 4-wires can, but you have to use a reversing relay to make them work.

Yes. The System Sensor 2WTAB is one. I think there are others. I have 6 of them in a 2 wire daisy chain. When one sounds, they all do. Unfortunately, to get this done, I had to hook them to a DSC panel that I installed just to support 2 wire smoke alarms since my Omni Pro II will not supports the sounder function on a 2 wire. Not they way I intended but I was stuck with a 2 wire setup in a new house.

 

[JohnnyMac]

2 wire smoke circuits are the way to go. Advantages? Lots. Less wire to run / a continuous circuit instead of numerous home runs. Easy detector wiring / in and out. If you run a 4 conductor you can return the circuit back to the control for full Class A supervision. 2 conductor - just terminate the last device with your EOL resistor. Still a fully supervised Class B circuit. In either case, you'll never need a power supervision relay. If you've got a 4 conductor circuit you can also use 2 wire smokes with internal sounders, return the trip to a reversing relay in the control and get one for all sounders. Better yet, just install enough interior speakers. Since smokes latch by nature, point zoning is not usually needed in a residential situation. You'll know which one tripped by the LED on the head. Even if point zoning is needed, I'd still use 2 wire detectors. Run them off of powered zone modules and get the benefits of "Clean Me" trouble alerts! Anything more extensive and you should get into a commercial fire panel. Which will give you... multiple powered outputs for 2 wire smoke circuits - the standard.
Good luck -
JMac