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Topic:
Security system questions ( smoke and carbon )
This thread has 16 replies. Displaying posts 1 through 15.
Post 1 made on Saturday September 15, 2018 at 19:41
FP Crazy
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Installing my own security system. Not really an expert at security.

I did not run for wire jumpers from one smoke detector to the next. I just homeran a 4 cond wire from each smoke back to the panel

I'm running short on zones so I want to combine all 5 smokes onto 1 zone. By combining all 12v+ and grounds together and then all supervised wires together to lay down on one of the zone terminals.

Here's what I know so far:

the smokes are a normal open circuit, that short when faulted (unlike glass breaks or motion sensors, which are normally closed)

I will need to put an EOL resistor across the terminals of the zone

This zone will need to be programmed as a smoke so it behaves accordingly

It will not be entirely supervised since the smokes don't feed each other, rather all common together back at the panel. But the system should still go into alarm when/if any of them detect smoke

This is a GE NX8E panel

The panel also has a + terminal to provide power to the smokes. Presumably to be able to reset (power cycle) the detectors when needed?

Bosch DS 285 smokes with DS292 mounting bases

More as the thread moves along

Thanks in advance
Chasing Ernie's post count, one useless post at a time.
Post 2 made on Saturday September 15, 2018 at 21:22
davidcasemore
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Yes, the smoke detectors get powered by the SWITCHED +12 VDC. That's how they reset after an alarm.
Fins: Still Slamming' His Trunk on pilgrim's Small Weenie - One Trunk at a Time!
Post 3 made on Saturday September 15, 2018 at 22:58
Ernie Gilman
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Other than that, I see no questions or problems.

The purpose of the EOL resistor is to have a set of detectors wired in series where shorting or opening the two wires causes an alarm. I don't get the need for this on a smoke alarm, but it's standard for burglar alarms: a thief can't bypass the alarm by either shorting together or opening wires. (There are still people who think that shorting means connecting two wires together and shorting means disconnecting one wire. If that's you, you're not going to understand this.)
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 4 made on Sunday September 16, 2018 at 01:29
Brad Humphrey
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On September 15, 2018 at 22:58, Ernie Gilman said...
I don't get the need for this on a smoke alarm, but it's standard for burglar alarms: a thief can't bypass the alarm by either shorting together or opening wires.

The reason it is code and HAS to be done, is the same as a thief... but the thief in this case is fire. If the fire is burning somewhere that would compromise the fire wire (before the detector has a chance to go off), then the panel will still trip and alert everyone before they are all potentially killed.
Post 5 made on Sunday September 16, 2018 at 01:37
Brad Humphrey
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John, as you know EOL means End Of Line. Which is where the resistors are suppose to go.
I see so many security companies putting all of them on the terminals at the alarm panel - which does no good what-so-ever. The saving grace is, it would take a smart thief who knows security systems to take advantage of that - and that assumes he can get to a wire for a zone he's trying to enter.
But on the fire alarm, please put the EOL were they are suppose to go. It is a pretty serious life/safety issue. Since you home run all the wires, you will need an EOL at each fire device (smoke, heat, etc.). But they are cheap and easy to slap in real quick, so shouldn't be an issue.
Post 6 made on Sunday September 16, 2018 at 03:25
Nick-ISI
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If the detectors are NO going closed in an alarm then to put them all on the same zone they will need to be wired in parallel.

If they are wired in parallel then you cannot put an EOL on each leg and expect it to work correctly. In fact there is no termination method that will work correctly in this scenario and each device should be placed on its own zone with its own EOL placed at the detector. You could put an EOL on one leg only and the circuit will work, but not all the cables will be correctly monitored for fault conditions, only the one you fitted the EOL on.

If the devices can be set to NC going open on alarm then they can be wired in series at the CP end and one EOL can be fitted, preferably at the end of the longest wire run.
What do you mean you wanted it on the other wall - couldn't you have mentioned this when we prewired?
Post 7 made on Sunday September 16, 2018 at 10:32
Ernie Gilman
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Well, half way, anyway.
Brad, Nick,
an alarm circuit that requires an EOL resistor is designed to see a certain range of resistance, what you'd expect the resistance of the series-run wire plus the EOL resistor to be. Resistance above or below the acceptable range triggers an alarm condition.

If the EOL resistor is placed in the alarm box and separate wires run in parallel to the sensors, the system won't protect against a wire being cut, since that won't raise the resistance seen by the alarm. It WILL protect against a short, though, since a short on any of the parallel wires will lower the resistance seen by the alarm to near zero.

If I had to guess and build an alarm system that didn't meet spec, I'd guess that a fire alarm that would indicate only shorts would work better than one that only indicated opens, since fire is more likely to melt insulation and create a short condition than melt copper and create an open. NEITHER OF THESE is acceptable, of course.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 8 made on Sunday September 16, 2018 at 11:09
Brad Humphrey
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On September 16, 2018 at 03:25, Nick-ISI said...
If they are wired in parallel then you cannot put an EOL on each leg and expect it to work correctly. In fact there is no termination method that will work correctly in this scenario and each device should be placed on its own zone with its own EOL placed at the detector.

If you use a EOL resistor 2x the normal value, then 2 circuits can be put on 1 zone in parallel and it works fine. i.e = 1KΩ is the EOL normally used, so put 2kΩ resistors at each detector.
That would get him down to only needing 3 zones for his 5 fire sensors. The increase in resistance would be enough to trip if 1 line went open.

Beyond that, you can use a zone expander if you really don't have enough zones to even get it down to that.
Post 9 made on Sunday September 16, 2018 at 11:38
Nick-ISI
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On September 16, 2018 at 11:09, Brad Humphrey said...
If you use a EOL resistor 2x the normal value, then 2 circuits can be put on 1 zone in parallel and it works fine. i.e = 1KΩ is the EOL normally used, so put 2kΩ resistors at each detector.
That would get him down to only needing 3 zones for his 5 fire sensors. The increase in resistance would be enough to trip if 1 line went open.

Beyond that, you can use a zone expander if you really don't have enough zones to even get it down to that.

Well first of all I was responding to him putting all the detectors on one zone, there is no EOL scenario to cover that.

Secondly the doubling of resistor value may or may not work as you are effectively halving the change seen by the panel, in your example one leg going open circuit will not then show infinite resistance, but 2K instead of 1K. Depending on the panels sensitivity to resistance (voltage) change on the zone this may not be enough to trigger a fault condition. If it doesn’t register this fault then you have a circuit that will not trigger the panel when the detector is triggered as it has an open circuit leg, but the panel is still seeing an EOL on the other leg that is sufficient for it to think it’s all good. On a life safety system I would not be prepared to take that risk....
What do you mean you wanted it on the other wall - couldn't you have mentioned this when we prewired?
OP | Post 10 made on Sunday September 16, 2018 at 12:02
FP Crazy
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These are NO detectors. No way to switch that.

I plan to put first floor 3 detectors on one zone, and 2 second floor detectors on a different zone. Since all wires on a given smoke zone will need to be wired in parallel (including the two supervised wires) I will need to put the eol somewhere. If I put it across the terminals of the supervised wires at one of the devices, and that leg burns open, then the panel will not see that eol. If I put the eol at the panel, and one of the legs burns open, then the panel will not see a closure from that smoke detector and go into alarm. If I put a resistor on each device (3 in parallel on floor1) then my total resistance would be way less than it wants to see (parallel wiring would drop it)

The panel came with 3.3k resistors which I am using on all other zones (doors, glass, motion, etc).

Unfortunately I don't have enough zones to give all 5 of them discrete zones.

I can give the Carbons (total of 2, 1 for each floor) discrete zones

I still need to buy 2 round ceiling mount Carbon detectors. Any brand model recommendations? I have 4 cond wire home run to each location
Chasing Ernie's post count, one useless post at a time.
Post 11 made on Sunday September 16, 2018 at 16:06
Brad Humphrey
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On September 16, 2018 at 11:38, Nick-ISI said...
.... the doubling of resistor value may or may not work as you are effectively halving the change seen by the panel, in your example one leg going open circuit will not then show infinite resistance, but 2K instead of 1K. Depending on the panels sensitivity to resistance (voltage) change on the zone this may not be enough to trigger a fault condition. If it doesn’t register this fault then you have a circuit that will not trigger the panel when the detector is triggered as it has an open circuit leg, but the panel is still seeing an EOL on the other leg that is sufficient for it to think it’s all good.

The resistance the panel is looking for is very specific. And it absolutely will trip with a change of 1/2 or 2x resistance. Several alarm panels use to have diplexing on their zones, where you could use 2 different value resisters on different devices and create 2 zones on a 1 zone input. Not sure if any of them are still doing that these days.

One could do resisters at 3x the normal for 3 devices on a single zone. Good chance it would work but as you said, that maybe getting a little to close to the detection threshold for comfort. Even if you did test it and it seemed to work.
Post 12 made on Sunday September 16, 2018 at 17:26
imt
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Not an alarm guy and also currently installing a new panel ELK from old Napco. Did you already buy the Smokes? If not, can't he use 2 wire smokes thus then running them in series and end in a loop back at the panel? I am using the System Sensor Cosmo smoke/CO2 detectors. Which uses the module so panel thinks its a 4 wire smoke zone anyway and can be used on any zone vs the limited 2 zone.
Post 13 made on Sunday September 16, 2018 at 17:40
Ernie Gilman
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On September 16, 2018 at 11:38, Nick-ISI said...
Secondly the doubling of resistor value may or may not work as you are effectively halving the change seen by the panel, in your example one leg going open circuit will not then show infinite resistance, but 2K instead of 1K. Depending on the panels sensitivity to resistance (voltage) change on the zone

This is totally the crux of the multiple resistor scenario. We don't know what the range of EOL resistance is that won't trip the alarm. That info is needed to know if two resistors could be used.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 14 made on Sunday September 16, 2018 at 18:44
Brad Humphrey
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On September 16, 2018 at 17:26, imt said...
Not an alarm guy and also currently installing a new panel ELK from old Napco. Did you already buy the Smokes? If not, can't he use 2 wire smokes thus then running them in series and end in a loop back at the panel? I am using the System Sensor Cosmo smoke/CO2 detectors. Which uses the module so panel thinks its a 4 wire smoke zone anyway and can be used on any zone vs the limited 2 zone.

I think he already has them all but even if he did, 2-wire smokes do not cost that much. So he could replace them all without breaking the bank.
Your idea would work but they are not technically in series. They are still wired parallel but in a daisy chain fashion. As an example, it would start with using the white/green to the detector, then the red/black from there back to the panel, which would tie directly to the white/green of the next detector, then red/black back again from there to the next again. Until we reach the final detector where the EOL is wired (or at the panel on the red/black back from the last one). Only the 1st white/green is connected to the alarm panel.
Post 15 made on Sunday September 16, 2018 at 20:32
davidcasemore
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On September 15, 2018 at 19:41, FP Crazy said...
Installing my own security system. Not really an expert at security.

For anyone else interested in fire alarm systems this site has a lot of good information and explanations :

[Link: douglaskrantz.com]
Fins: Still Slamming' His Trunk on pilgrim's Small Weenie - One Trunk at a Time!
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