old 2 wire smoke on zone 16 of M1G

[m1u]

I am swapping an Elk M1G in for an old panel, and the old system includes a 2 wire heat sensor, mounted right over the furnace. It is a Fire Systems Model 604, and the two wires went on from that to go to the power input of a series of 4 wires smokes elsewhere in the house. Googling, 604 is long since discontinued, but I did find some pdfs on line for a seemingly identical model, Chemtronics-600-Heat-Detector (cocoontech.com won't let me paste in a lnk as I'm new to this site)

Certainly I can take the 4 wires smokes and wire them up as I like to other zones, leaving me with this 2 wires sensor as a standalone problem to deal with. What is the best way to deal with it:

1. Toss it, and replace it with a conventional smoke detector. The old furnace used to be oil, but the new one is high efficiency/propane, so I don' t think falsing would be a problem? Or is there something desirable about a heat sensor instead of smoke for use over a furnace, and I should find some modern 4 wire heat sensor?

2. Keep it, and wire it up to zone 16 with an 820 ohm resistor as described in the Elk manual. If so, two questions... the manual page 6 mentions various compatible models, and does not mention mine. Is that a problem, is 604 not compatible if not listed? Also, how critical is the value of the 820 ohm resistor... can a 1K be used instead?

Thanks for your help!

 

[gatchel]

If it's not listed in the manual, don't use it. 2 wire smokes are cheap. I would install a new one. Also, the manual says 820 ohm, I would use that resistance as it probably has something to do with the supervision of the zone (duh) and also to allow the panel to power the smokes properly.

 

[m1u]

OK, but if I have to replace it, I actually have plenty of wires going to it... presumably a new 4 wire sensor is better than a new 2 wire sensor? And what about the smoke vs heat issue, what is best for this application over a high efficiency propane furnace?

 

[Del91574]

A hardwired heat detector is a fusible link. It will work on a 2 or 4 wired circuit, so you can put it on any zone defined as "4 wire fire". The EOLR will be installed at the unit itself, since you only have a pair of wires to it.

I'd keep it as a heat detector, however if you're looking at swapping it for a smoke, then it'll be a 2 wire model, with the compatible and listed units in the documents from Elk.

 

[m1u]

So this device is just open circuit normally, and something melts and shorts when there is a high temperature? OK, I understand how to wire that up with EOLR to any available zone.

It sounds like even though this heat detector can be wired up with just 2 wires, that "2" is just a coincidence: it isn't a "2-wire smoke" in the sense that the M1G docs are talking about, where it has to be on zone 16, one of a listed set of models, and you flip the "2-wire on zone 16" panel switch? Unlike the fusible link I have, those 2-wire detectors must have some active components that require power to run, and by flipping that switch on the panel will make it supply power to zone 16 while also being able to sense if they trip somehow via the current drain?

 

[Del91574]

yes

 

[Spanky]

The different models of two wire smokes have different current draw and trip points. UL requires that the two wire input characterics of the control match the current and trip points of the two wire smokes. All two wire smokes on the market are not tested for compatibility.

Any 4 wire smoke will work on the M1. The trip circuit is an open circuit that shorts to cause an alarm. You can also put any four wire smokes on any zone so that you can zone out the smoke zones and not just have to use zone 16.

I think two wire smokes are over sold in that if you can get two wires to the location, you probably can get 4 wires or CAT5 to the same location.

 

[Del91574]

*Category cable is not suitable for fire alarm*

Not to argue the point, but a 2 wire vs. 4 wire fire circuit is a valid point, however I will state the following based on my experience.

Wiring conventional fire alarm using multiple fire zones isn't commonplace in my state, and I will say, not practical IMHO when wiring a house to meet present code in new construction, as well as factoring in reversing relays and EOL supervision. When you move to a retrofit situation where running cabling on multi-story houses with few chases, the problem of maintaining a continuous loop by pulling 2 cables or an 18/8 to maintain a proper circuit is difficult, albeit sometimes impossible.

The big thing about a 2 vs. 4 wire circuit is simplifying the process of maintaining a proper supervision circuit, especially when you mix in multiple heat detectors and combine it with someone that doesn't completely understand how to wire a fire circuit correctly, even in the trade it is commonplace for installers to omit EOL relays or T-tap the circuits.

I always wire with an 18/4 and try to run a continuous loop wherever possible, however if running a 4 wire loop, it's a one shot deal if a wire gets hit or has an issue, where at least on a 2 wire loop, you have options.

Now if Elk would have a module or option like many manufacturers to have multiple 2 wire fire loops or even run SLC's, it'd add to the robustness and flexibility of the M1 and facilitate more installations where I am taking over other panels.