trouble finding power supply for smoke detector

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Old 02-14-18, 01:42 PM
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trouble finding power supply for smoke detector

I'm hoping someone can help. I'm trying to replace my smoke detectors that have an A/C power supply. I live in a condo. I've opened all electrical breakers to my unit to secure the power and I believe its mainly powered off of the lighting circuit. However, I'm still detecting a small amount of voltage. I only have a voltage detector pen but its beeping on the 12-100V range. Also, the smoke detector light goes out but when I push the test button it still beeps. Does anyone have any information on where an external power source would be for the whole building? Is there a backup battery for the whole building perhaps? Any help would be greatly appreciated
 
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Old 02-14-18, 02:22 PM
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Welcome to the forums.

I just replied to a similar thread.
Interconnected smoke detectors are supposed to get their power from a lighting circuit.

It would be pretty hard to tell you where to find your power source. I would start by identifying the wiring at all the detector locations. Typically you'd find a two wire and three wire cable at the first location that receives power. You'd find 2) three wire cables between each unit and a single three wire cable at the last location.

Are you sure these are 120v/battery backup units ? They should have a red, black and white wire. These type use an internal 9v battery. No building backup.
 
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Old 02-14-18, 02:40 PM
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More specific question, is it common in an apartment complex, condo, etc. for the smoke detectors to have a common backup power source for all units?

I've already shut off all power within my unit and yet it's still working, I've contacted my HOA and they tell me no but I also don't trust them to actually look into it.
 
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Old 02-14-18, 02:44 PM
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Each apartment or condo would have it's own internally contained system. House would protect common hallways and areas.

When your detectors are power with AC.... the LED should light up green and blink red once every ten seconds if the battery is ok.
 
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Old 02-14-18, 02:45 PM
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No, 120v interconnected smoke alarms are generally only powered from the breaker panel in the specific dwelling unit. Is it possible that these are low voltage devices, and are powered from your security system? Brand and model number would help in giving you advice.
 
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Old 02-14-18, 03:04 PM
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The detector is a firex 120-1182. I do not have a security system for my unit alone, only for the whole building.
I'm at a loss so I'll be calling someone. I'll give an update if we figure out the problem.
Thank you for your help.
 
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Old 02-14-18, 04:18 PM
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So... residual energy. I'm glad I figured it out myself to save the money but of course feel silly it took so long for me to figure this out. But hopefully this will help someone else in the future.

With the power off and batteries removed the smoke detectors had enough residual energy to beep for over an hour.
 
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Old 02-14-18, 05:05 PM
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Yes, they can and will do that.
 
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Old 02-14-18, 06:39 PM
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They will beep for quite a while unless you hold the test button in and that should quiet it almost immediately.
 
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