Heat Detector Wiring. I'm Stumped

[mkgrady]

I can't figure this out. I needed to add a light in my attached garage in the ceiling. No easy place to pick up a circuit so I went to the heat detector. One of the two detectors has only a 14-2 NM connected, so I wondered how it can signal the smokes in the rest of the house. The other one has two 14-2 NM's connected. I don't understand why this house built in 1997 doesn't have the typical 14-3 NM run to every smoke or heat detector, but it gets worse.

Voltage to the heat detector is 120 hot to egc. Voltage on white wire is 120 volts to egc. I looked at the other heat detector and found one of the two whites disconnected. Thinking it just came loose during installation I reconnected it. As expected I still did not get 120 volts from hot to white wire.

It appears the HD's are wired like a switch leg (no neutral present) where both sides of the switch are hot when the switch is closed. I can't make any sense out of this. I can't imagine how they can even function or figure out a way to test them as they do not appear to have a test switch.

 

[jaylectricity]

Try a non-contact tester against the EGC. Or run an extension cord and test voltage of each conductor against the ground of the extension cord.

You may find that the ground is either being used as the hot, or it's the signal wire.

 

[mkgrady]

Try a non-contact tester against the EGC. Or run an extension cord and test voltage of each conductor against the ground of the extension cord.

You may find that the ground is either being used as the hot, or it's the signal wire.

I don't follow you. I tested with a volt meter from hot to ECG and white wire to ECG and read 120. A non contact tester gave me a hot reading on hot and white just like you would find on a switch leg. It does look like the white wire is being used as hot but I don't get the purpose of this. I also don't understand the meaning of it being used as a signal wire.

 

[J.P.]

Did they maybe use the ground as a neutral and either the black or white as a signal wire?

For those to work you need a:
Hot.
Neutral.
Signal wire. The signal wire carries a signal when one HD goes off and makes them all go off.

The reason your black and white don't read to each other is most likely that they are on the same phase / same breaker in your case.

Somebody probably messed up in their jury rigging when wiring your house.
Start closest HD to the panel and see what you have there.

 

[mkgrady]

The EGC is just spliced through with no connection to the HD like you would expect. The heat detectors don't even have a place for the signal wire. They have four screw terminals. What kind of HD only has two connection points and no way to signal the smokes in the house?

I'm beginning to think I am stumped because this is totally screwed up with no way to make sense of it. It appears these two heat detectors should have been wired with 14-3, the HD's should be typical 3 wire that interconnect with all the other hard waited detectors, and I will have to make the changes. But I'm still stumped on what these HD's are meant to do and how they are meant to work.

 

[kwired]

The EGC is just spliced through with no connection to the HD like you would expect. The heat detectors don't even have a place for the signal wire. They have four screw terminals. What kind of HD only has two connection points and no way to signal the smokes in the house?

I'm beginning to think I am stumped because this is totally screwed up with no way to make sense of it. It appears these two heat detectors should have been wired with 14-3, the HD's should be typical 3 wire that interconnect with all the other hard waited detectors, and I will have to make the changes. But I'm still stumped on what these HD's are meant to do and how they are meant to work.

If your heat detectors have 4 terminal screws, that sounds a lot like they are heat detectors for low voltage/power limited fire alarm systems, they are nothing more than a normally closed contact device that opens on heat rise, they will do nothing when intermixed with your typical self contained - interconnected smoke alarms, in fact depending on exactly how they are connected they will actually do the opposite of what is desired, meaning if there is a rise in heat condition in your garage - they very well could interrupt power to the rest of the circuit when they open their contacts leaving you with no alarms at all.

Had a brain fart, the units I was talking about are not normally closed they are normally open, and an end of line resistor is used to monitor the condition of the circuit. In normal operation of that kind of system the main controller is looking for continuity through the end of line resistor if that is lost it results in a "trouble" signal at the main controller, but if the two lines of the detection circuit are shorted, normally by closing a sensor device, but any other short will do the same, then the main controller sends power to the alarm devices.

Either way though this is likely not a detector being used as designed.

 

[K8MHZ]

I can't figure this out. I needed to add a light in my attached garage in the ceiling. No easy place to pick up a circuit so I went to the heat detector. One of the two detectors has only a 14-2 NM connected, so I wondered how it can signal the smokes in the rest of the house. The other one has two 14-2 NM's connected. I don't understand why this house built in 1997 doesn't have the typical 14-3 NM run to every smoke or heat detector, but it gets worse.

Voltage to the heat detector is 120 hot to egc. Voltage on white wire is 120 volts to egc. I looked at the other heat detector and found one of the two whites disconnected. Thinking it just came loose during installation I reconnected it. As expected I still did not get 120 volts from hot to white wire.

It appears the HD's are wired like a switch leg (no neutral present) where both sides of the switch are hot when the switch is closed. I can't make any sense out of this. I can't imagine how they can even function or figure out a way to test them as they do not appear to have a test switch.

A make and model # may lead to a manual and explain at least some of this.

 

[goldstar]

It appears the HD's are wired like a switch leg (no neutral present) where both sides of the switch are hot when the switch is closed. I can't make any sense out of this. I can't imagine how they can even function or figure out a way to test them as they do not appear to have a test switch.

If they're 120V there must be a module somewhere that ties into the smoke alarm circuit. As you suspected, that is just a switch leg that probably triggers the module.

 

[mkgrady]

If your heat detectors have 4 terminal screws, that sounds a lot like they are heat detectors for low voltage/power limited fire alarm systems, they are nothing more than a normally closed contact device that opens on heat rise, they will do nothing when intermixed with your typical self contained - interconnected smoke alarms, in fact depending on exactly how they are connected they will actually do the opposite of what is desired, meaning if there is a rise in heat condition in your garage - they very well could interrupt power to the rest of the circuit when they open their contacts leaving you with no alarms at all.

Had a brain fart, the units I was talking about are not normally closed they are normally open, and an end of line resistor is used to monitor the condition of the circuit. In normal operation of that kind of system the main controller is looking for continuity through the end of line resistor if that is lost it results in a "trouble" signal at the main controller, but if the two lines of the detection circuit are shorted, normally by closing a sensor device, but any other short will do the same, then the main controller sends power to the alarm devices.

Either way though this is likely not a detector being used as designed.

I have seen that type of detector before but it did not operate on 120 volts, which is what I measure at the detector. Also I don't have a fire alarm control panel (I do have a security panel that I have never used).

 

[mkgrady]

If they're 120V there must be a module somewhere that ties into the smoke alarm circuit. As you suspected, that is just a switch leg that probably triggers the module.

I'll start looking for a module. I guess I'll start at the nearest smoke detector. Can't imagine where else it could be. I suspect these things don't do anything and where just wired and put in place to pass inspection. Pretty strange if that is the case as the rest of the house looks to have decent wiring.

 

[jaylectricity]

I don't follow you. I tested with a volt meter from hot to ECG and white wire to ECG and read 120. A non contact tester gave me a hot reading on hot and white just like you would find on a switch leg. It does look like the white wire is being used as hot but I don't get the purpose of this. I also don't understand the meaning of it being used as a signal wire.

According to your 2nd, 3rd, and 4th sentences, you follow me fine. I was just giving suggestions. You didn't say you had used a non-contact in your OP. I used the info you gave me and tried to think of things that maybe you hadn't thought of...like somebody being dumb enough to use the ground as a hot.

Signal wire = red wire; in your standard 14-3 Romex smoke/heat/CO detection circuit.

Maybe you had read voltage through the signal wire because there was a load.

 

[wallypiper]

I have just been looking at a heat detector for a possible project. The one I have literature on is a Fenwal.
It can be purchased with either a NC switch which opens or a NO switch which closes on heat rise. For a typical fire alarm system you use NO and wire multiple sensors in parallel. Any sensor can close the circuit and signal the system.
If you want to break a circuit, say the heat to some kind of furnace or maybe a heated chemical bath, you use the NC version and wire multiple sensors in series. Any sensor can open the circuit and, typically, de-energize a contactor or relay that controls the heater.
It was my impression that they all ship with two leads on each side but the second lead isn't used on the NC version. That could be wrong. I have only seen the very simple and generic installation instructions. But the rest of the above is correct. An "end of the loop" device of some sort was shown on the parallel wiring diagram. I don't know enough about fire alarm systems to know why it's there but assume some alarm systems require some conductivity through the loop all the time to verify that power is available all the way to the last detector on the circuit.

w piper

 

[kwired]

I have seen that type of detector before but it did not operate on 120 volts, which is what I measure at the detector. Also I don't have a fire alarm control panel (I do have a security panel that I have never used).

What does the "switch" connect between? It sounds like it is not a stand alone "detector" but rather is a "sensor" that must connect to some other component, it may or may not be used according to it's ratings, but still sounds like what you would see for heat sensing for a "supervised" zone of a fire alarm system. The four terminals is what gives this away. Two terminals for each side of the switch. You connect one two wire cable each side of the switch, and the second cable to the remaining two terminals. If this device happens to be the "end of the line" of the zone then the EOL resistor goes between the remaining two terminals. A "supervised" zone has constant current flowing through it to prove the integrity of the zone, should any connection become compromised a change in that current tells the controller there is a problem in that zone and it gives a trouble alert.

I really can't say I have installed heat detectors that integrate with household type smoke alarms, but I would think they would be stand alone detectors with optional interconnect lead and an alarm device within the same unit, just like the other smoke alarms have and not four terminal screws. If it is something that ties into the other smoke alarms and is a sensor only there about has to be some kind of relay module it connects to to make it integrate with the others.

 

[mkgrady]

Having no fire alarm control panel and only 14-2 run to theses detectors, and finding 120 volts at the detectors, my thinking is that these detectors do nothing and were just put there to pass an inspection. I won't know until I have time to pull it all apart and trace the wires

 

[kwired]

Having no fire alarm control panel and only 14-2 run to theses detectors, and finding 120 volts at the detectors, my thinking is that these detectors do nothing and were just put there to pass an inspection. I won't know until I have time to pull it all apart and trace the wires

A lot of good that inspection did if it never worked from the start. Don't they do a performance test of those items?

 

[handy10]

Have you checked Google to see if you can find a wiring diagram?

 

[mkgrady]

A lot of good that inspection did if it never worked from the start. Don't they do a performance test of those items?

The fire department checks operation of smokes but I'm not sure if they check heat detectors

 

[gar]

140214-2353 EST

This thread is a good illustration of why an understanding of fundamentals is important and why one needs to know what is inside a device and how it works.

In the case of this heat sensor it is necessary to know what is inside the device. A datasheet is a good starting point. If not available or incomplete then on a simple device make external measurements. In this case we can suspect internal mechanical contacts, or possibly some special electronic component.

For this product I would first test it disconnected from its present circuit. Do a resistance check between all combinations of terminals at room temperature and a temperature above its trigger point. Quite likely it is some form of bimetal thermally sensitive snap blade switch with no electronics. How the present external circuit wires are connected to the sensor may be an indicator of what is inside. Is there anything special about the circuit wiring at the last sensor on the circuit?

If a simple external test does not indicate what is internal, then it should be opened for further analysis.

Analysis can be difficult if there is complicated internal electronic circuitry.

.

 

[goldstar]

A lot of good that inspection did if it never worked from the start. Don't they do a performance test of those items?

Performance test ??? Wow, you really do live in Nebraska don't you.

Most of the inspectors in my area want to pull up to the job, go inside for a quick inspection and be back out to their car and have the same song still playing on the radio :lol:

 

[kwired]

Performance test ??? Wow, you really do live in Nebraska don't you.

Most of the inspectors in my area want to pull up to the job, go inside for a quick inspection and be back out to their car and have the same song still playing on the radio :lol:

Electrical inspector is not going to do any performance test of smoke alarms or fire alarm systems, but some other fire/building inspector likely would, especially if it is a real fire alarm system. I do understand in the OP this is something in a dwelling and could be misapplied and could be missed, but if it were a fire alarm system in a public access building the fire marshal does come around periodically and do some performance testing as well as at initial installation, I don't know if they would apply some heat to heat detectors or not as a part of that test, but I know they activate all manual stations, and likely use some canned smoke to activate smoke sensors.