Elk with 2-wire smokes not alarming


Active Member
Hello. I have 3 Bosch DS282THS' with a 680ohm terminating resistor hooked to an M1G with FW 4.4.4.

I test the detectors individually and they go into alarm and the monitored voltage on Zone 16 (set with the 2 wire jumper) goes from 12.2v to 9.6v, but the panel doesn't show a fire alarm.

Am I missing something?

I do notice that while my version of the manual says the M1 supports this model of detector with the 680ohm resistor, newer versions of the manul do not list this detector and now call for an 820ohm resistor. So, I did the same test with an 820 EOL and the M1 still doesn't report an alarm. I don't remember what the voltages were though.

I sent this in to Brad via email, but thought the folks here might point me in the right direction in the interim.

Do you have Zone16 defined right in RP?

Definition: 10=Fire alarm
Type: 6=2-Wire smoke on Zone 16
For UL listing of the M1, the voltage parameters were tightened up to match the listed 2 wire detectors in the manual. You may have a detector that does not pull the line low enough to activate the alarm.

See if your detector is on the list of UL detectors for the M1.
Hello Spanky. Thanks for the note.

Well, they were on the list when I bought the panel. I double checked the hardcopy manual that shipped with it.

However, they are not on the current .pdf manual.

What's the next step?
If you updated the M1 software, the new UL smoke threshold levels were loaded into the M1. These are not user changeable.

Verify operation:
Short the two wire circuit at the 820 ohm EOL resistor. The fire alarm should activate. Make sure you have informed the central station that you are testing.

What could be happening:
The smoke detector is not pulling the two wire fire circuit low enough in voltage with an 820 EOL resistor to reach the threshold alarm level of the M1. You can verify that this is the case by TEMPORARILY replacing the the 820 ohm EOL resistor with a larger resistor, say 1000 ohm EOL resistor and test the results. If you do not have a 1000 ohm resistor for testing, place two of the M1's 2200 ohm EOL resistors in parallel which will give you 1100 ohms.

If you find that the alarm point is reached with a 1000 ohm resistor, your smoke detectors would probably not work with a 680 ohm EOL resistor.

There was a great deal of smoke detector testing required in order to meet the UL requirements.

The corporate response of what to do next is: Replace the smoke detectors with a UL smoke detector on the list of approved smoke detectors.
Spanky, thank you very much for the detailed info. I'll go through the testing process tomorrow and report back what I find.
Spanky, thanks again for the info.

As suspected, shorting at the EOL triggers the panel. So wiring, panel and setup are fine.

Swapped the EOL for a pair of 2.2k's for effective 1.1k and voltage reads 12.9 normal and drops to 10.0 during alarm and still does not trigger the panel.

I appreciate the corporate response though wish there was another option since these detectors *were* listed as compatible in the manual at the time of purchase.

Is there any other work around while I ponder replacing the detectors?

I am not sure how much you could get for your Bosh Detectors but I have seen the System Sensor 2WT-B's that I believe are compatible with the ELK for about $30 each (lowest I have seen them and I forget where to be honest).

I currently have a panel at UL being tested with this model System Sensor Detector (very expensive BTW and very time consuming (6 months plus)). Spanky knows that pain as well.

The problem with 2 wire smoke detector compatibility with a panel for UL Listing is that if you design a panel to meet UL Requirements with one detector you may no longer meet the UL Requirements or function at all with another. There is a big difference from detector mfg/family to detector mfg/family and thats why UL tests them and controls the combination in UL applications.

You do not have these issues with 4-wire detectors but then you need EOL Relays etc.

If I remember correctly the Bosch Detector may be good for a GE Caddix panel so maybe someone could use them.
Digger, thanks for the input too.

Yes, I'm sure the UL requirements are no fun. It's also no fun, but admitedly cheaper, to replace a set of smokes.. Just not "fair" that I procured what the manual said and now they don't work. ;)

I'll start researching 2 vs. 4 wire before looking at replacements. I think I was enamored of the "clean me" signalling in the 2 wire and had thought the M1 supported that at the time.
ELK was forced to change the firmware to meet the UL requirement for 2 wire smokes. Not that there was anything wrong with the way it was but it just didnt meet the UL Requirement. The trip window is extremely tight now as Spanky stated.

My personel experience is that just because something does not meet code or an agancy requirement (like UL) does not mean its unsafe. Also just because it does meet code or an agency requirement does mean it is safe.

How many smokes are you planning on?
Digger, thanks for the last post, I hadn't seen it until now. The install has 3 smokes in it today.

We're planning another trip out to the location of this install and I'm returning my attention to replacing these smokes as the current ones don't trip the Elk.

The current Elk docs say the 2W-B and the 2WT-B are compatible.

Spanky, could you please comment on compatability of the 2WTA-B? This is the same as the 2WT-B with an internal sounder. I'm presuming this would not be a UL listed (tested) configuration, but would it function? It seems to have the same max current when in alarm as the non-sounder versions listed.

I have the specs for the two System Sensor Detectors at work. I will try and dig them out tomorrow. Its public information so I dont have a problem sharing it.

My evaluation at UL is still ongoing (about 7 months now) so I dont have any information to compare yet (if our panels would work with both detectors etc). I am hoping UL finishes sometime before I retire (in 20 yrs).

Spanky can understand my frustration since he has been there and done that with them.
I have recently installed 6 2WTA-B's in series on an ELK using the the RRS-MOD from System Sensor to make all the sounders activate when any one detector activates and it works like a champ.
acdcelectric said:
I have recently installed 6 2WTA-B's in series on an ELK using the the RRS-MOD from System Sensor to make all the sounders activate when any one detector activates and it works like a champ.
You must have some special mojo, or I have a defective RRS-MOD. I was never able to make it work. Would you care to share how you wired it?