Heat Detector Wiring. I'm Stumped

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140215-1225 EST

If you reference wallypiper's link and go to http://www.fenwalcontrols.com/utcfs/ws-375/Assets/DAF_install_vert.pdf , then the wiring of the likely sensor is shown. See page 2 figure 3. The description in post 1 of this thread is of the two wire wiring without the endpoint resistor, and the sensors are normally open below the threshold temperature. Since the normally open sensors are in parallel this is a positive logic inclusive OR circuit.

That 120 V or thereabouts is measured on both the white and black wires could mean that there is no load on the output of this circuit, and that capacitive coupling from one wire to the other produces about 120 V on a high impedance meter. Whether capacitive coupling is producing one of the 120 V readings can be determined with a 25 W 120 V test light.

If the sensors are really a normally closed contact at room temperature and wired in series (lower left circuit), then more clarity is need on the circuit wiring to the sensors. If normally closed contacts are wired in series, then this is still an inclusive OR circuit, but using negative logic.

Inclusive OR means the output of the OR circuit is TRUE if any one or more inputs are TRUE, and only FALSE if all inputs are FALSE. An exclusive OR (XOR) logical function can only be defined for two inputs. The XOR output is TRUE if one or the other input is TRUE, and is FALSE if both inputs are FALSE or if both inputs are TRUE.

One needs to find out where the temperature sensing network terminates, and what it is controlling. Does it directly control an alarm bell and/or light, or does it connect to some alarm system.

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I bought this spec. house new 15 years ago. It doesn't have a FA system. I won't know what these two heat detectors are connected to until I start tracing the wires that feed them. When I find the source I suspect I will find the 14-2 is run to the nearest hard wired 120 volt smoke. I suspect the white wire is not connected as this seems like it would be a dead short circuit ( assuming normally closed contacts on the HD) hot to neutral.

Thanks to all for the input. It has helped me to form the opinion that this is a screwed up installation. The rest of the house wiring seems fine (so far).
 
140215-2123 EST

mkgrady:

I believe your heat sensor is a normally open switch. You can easily determine this by disconnecting the two wires from the last sensor, and testing the sensor.

I don't know the numbering so I will simply assign arbitrary numbers. Make the two terminals with attached black wires 1 and 2, and the white wires 2 and 4. I believe that 1 and 2 are internally connected together and to one side of the NO sensor switch. And 3 and 4 are internally connected together and to the other side of the NO switch.

Thus, 1 to 2 should be near zero resistance, and 3 to 4 also near zero resistance. At room temperature the resistance from 1 or 2 to 3 or 4 should be very high. When the sensor temperature is raised above the threshold sensing level, then the resistance from 1 or 2 to 2 or 4 should be very low. A heat gun could be use to raise the temperature. Note the output temperature close to the nozzle of the heat gun is very hot, possibly 800 F. It can melt plastic. A hair dryer output is about 180 F on high.

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mkgrady said:
I bought this spec. house new 15 years ago. It doesn't have a FA system. I won't know what these two heat detectors are connected to until I start tracing the wires that feed them. When I find the source I suspect I will find the 14-2 is run to the nearest hard wired 120 volt smoke. I suspect the white wire is not connected as this seems like it would be a dead short circuit ( assuming normally closed contacts on the HD) hot to neutral.

Thanks to all for the input. It has helped me to form the opinion that this is a screwed up installation. The rest of the house wiring seems fine (so far).
Click to expand...


This sounds about right.

Maybe they sent the new guy out and he didn't know any better.

You might get lucky and the 14/2 wont be stapled anywhere and you can use it to pull in the correct wire and save some attic creeping.
 
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mkgrady said:
I bought this spec. house new 15 years ago. It doesn't have a FA system. I won't know what these two heat detectors are connected to until I start tracing the wires that feed them. When I find the source I suspect I will find the 14-2 is run to the nearest hard wired 120 volt smoke. I suspect the white wire is not connected as this seems like it would be a dead short circuit ( assuming normally closed contacts on the HD) hot to neutral.

Thanks to all for the input. It has helped me to form the opinion that this is a screwed up installation. The rest of the house wiring seems fine (so far).
Click to expand...
You can't determine with an ohmmeter/continuity tester that you have found the same segment of a circuit? True it will not tell you everything that is hidden, but in most cases isn't too hard to determine the logic of the installer and have a pretty good idea of what you have.
 
kwired said:
You can't determine with an ohmmeter/continuity tester that you have found the same segment of a circuit? True it will not tell you everything that is hidden, but in most cases isn't too hard to determine the logic of the installer and have a pretty good idea of what you have.
Click to expand...

I can figure it out once I take the time. Because it is my own home I will get to it but it is not urgent. This forum discussion has helped me confirm that whatever wiring I have to these SDs it is probably screwed up and I will have to fix it.
 
mkgrady said:
I can figure it out once I take the time. Because it is my own home I will get to it but it is not urgent. This forum discussion has helped me confirm that whatever wiring I have to these SDs it is probably screwed up and I will have to fix it.
Click to expand...

Most all smoke detectors today use a 9vdc interconnect signal to trigger the other smokes, this signal is sent between the red/yellow wire DC+ and the white neutral DC- if 120 volts has been applied to the red wire then most likely the interconnects have been compromised, the only way to trigger a smoke through the interconnect is with a 9vdc source such as using a 9 volt battery to the red and white wires with the + on the red, I have used this method to test many smokes we changed out to see which ones had a failed interconnect.

So there is no real way to interface a HD to a set of interconnected 120 volt smokes without some kind of interface that would provide the 9vdc signal for the interconnect, if the HD's were wired to send 120 volts to the interconnect then most likely the interconnect will be failed if the hd's were ever triggered.
 
mkgrady said:
I can figure it out once I take the time. Because it is my own home I will get to it but it is not urgent. This forum discussion has helped me confirm that whatever wiring I have to these SDs it is probably screwed up and I will have to fix it.
Click to expand...
I thought from reading your early posts that you already figured it likely was screwed up:happyyes:

hurk27 said:
Most all smoke detectors today use a 9vdc interconnect signal to trigger the other smokes, this signal is sent between the red/yellow wire DC+ and the white neutral DC- if 120 volts has been applied to the red wire then most likely the interconnects have been compromised, the only way to trigger a smoke through the interconnect is with a 9vdc source such as using a 9 volt battery to the red and white wires with the + on the red, I have used this method to test many smokes we changed out to see which ones had a failed interconnect.

So there is no real way to interface a HD to a set of interconnected 120 volt smokes without some kind of interface that would provide the 9vdc signal for the interconnect, if the HD's were wired to send 120 volts to the interconnect then most likely the interconnect will be failed if the hd's were ever triggered.
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Can't say I know what is available for heat detection to interconnect with the typical smoke alarms, but kind of assume it is a 120 volt powered device with same interconnect circuitry as the smoke alarms, I still think OP has a heat detector designed for a low voltage/power limited fire alarm system somehow tied into his smoke alarm circuit, and I'd bet they will not do what was intended either if ever called upon to operate.

Add: sure looks like items like I suspected would be the standard thing to use for OP's application do exist: http://www.brkelectronics.com/product/HD6135FB
 
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