Configuring CO loop on NX8E

use 2 zones?

One problem with wiring the trouble relay on the CO detector into the alarm circuit is that a trouble condition at one detector can block an alarm at a detector farther from the panel. You might want to consider using a separate trouble loop, wired to another zone. If you have lots of spare zones at the panel but the wiring is already in place, this can be done using only 4 wires. Connect power for the detector in the usual manner. If the panel uses a common negative for the zone loops, connect positive to the appropriate power terminals the negative at the detector to "C" on both the alarm and trouble outputs. Return "NC" from the alarm amd trouble relays on the two remaining wires.

only if form C relay. how does that double eol circuit option work?

I've used this trick ("borrowing" from the power negative terminal) in cases where a customer wanted an additional Motion Detector near an existing one, in order to meet my requirement for placing the 2nd MD on its own zone.

I've also used the same trick when installing a new CO unit above an existing NX8E Keypad. I feed the CO with 12vdc from the pad, feed the negative to the CO relay terminals, and ship the signal back to the panel on the unused 4th wire of a standard quad cable (keypad only requires three conductors).

To reiterate my orig>> CO Detectors are available with an

circuit is that a trouble condition at one detector can

consider using a separate trouble loop, wired to another

in place, this can be done using only 4 wires.

negative for the zone loops, connect positive to the

alarm and trouble outputs. Return "NC" from the alarm

The disadvantage of using only four conductors in the standard configured loop with the eol resistor at the CO unit is that if I run the loop through the contacts of the relay, it will give an alarm signal when power fails or for some other internal problem unrelated to the presence of CO.

Therefore you can plainly see that if I wish to avoid sending the fire department using the configuration in the previous paragraph I can not make use of the trouble relay contacts -- which is a terrible waste of good engineering and leaves the homeowner vulnerable to a unit that someday will faill -- and I and the homeowner won't know about it.

circuit is that a trouble condition at one detector can

consider using a separate trouble loop, wired to another

in place, this can be done using only 4 wires.

common negative for the zone loops, connect positive to the

alarm and trouble outputs. Return "NC" from the alarm

The Honeywel (nee Ademco) Vista 15 & 20s have a smilar problem . We use a CO detector (the C0Star 12SIR) that has 2 Form C relays for Alarm and Trouble. You can hook it to the panel and wire it so that the Trouble Relay is N.C. and the Alarm Relay is N.O. on a single zone with that zone programmed as CO and it works fine.

BUT.... do the same thing on a zone expander and if the Trouble Relay opens and THEN the Alarm Relay closes the zone goes into trouble and never goes into alarm. In order to get the zone to go into alarm at this point you have to restore the EOL (even for just a second). When you push the test button on this detector it does precisely that - goes into trouble for 5 seconds and then into alarm - then the customer calls and asks if the Monitoring Center got the alarm and the answer is "No".

This little flaw is completely undocumented in the Installation manual and when we discovered it and called Tech Support about 4 years ago they had never heard of it. Since then Honeywell has done nothing to correct the firmware or put a warning in the manual that this configuration should not be used on a zone expander. This despite my continual hounding of their reps every chance I get "oh-oh, here comes old whatshisnuts again" is probably what they say when I come around the corner at a trade show.

It might. McDonalds lowered the temperature of their coffee.

It's a catch 22 type situation. One method can cause an unwanted alarm. Another can make the system miss an actual alarm. Because of that I much prefer to keep alarm and trouble on separate loops. You could get around that on a commercial system using a class A fire loop but then you have the issue of a CO detector on a fire alarm zone.

About the only solution I have come up with is to use separate zones.

well that's what you're gonna hafta to do [2 zones] if you wanna to do it right.