WiremanWireman · Interconnected smoke alarms not all sounding: troubleshooting for electricians · 2023 NEC ·
Interconnected smoke alarms not all sounding
The interconnect wire, mixed brands, alarms on different circuits and failed units.
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How it works
Hardwired interconnected alarms share a third wire, the interconnect (usually red in a 3-conductor cable), that carries a signal from whichever alarm detects smoke to all the others. The signal is specific to each manufacturer, so mixing brands usually doesn’t work. If the red wire is broken, loose, or never connected at one box, the alarms past that point won’t sound when another one triggers.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Press the test button on one alarm. Which others sound?
- None of the othersAre all the alarms the same brand, or listed as compatible with each other?
- Mixed or unknown brandsIncompatible alarms
- All the same brand or listed compatibleTest: Inspect the interconnect at each box
- Loose, capped or missing interconnectInterconnect not connected at a box
- All connectedTest: Test the interconnect wire for continuityExpect: A low reading, a few ohms or less, at every box on the same cable run.
- Open (OL) at some boxesBroken interconnect conductor
- Continuous everywhereAn alarm isn’t sending or receiving
- Some sound, some don’tAre all the alarms the same brand, or listed as compatible with each other?
- Mixed or unknown brandsIncompatible alarms
- All the same brand or listed compatibleTest: Inspect the interconnect at each box
- Loose, capped or missing interconnectInterconnect not connected at a box
- All connectedTest: Test the interconnect wire for continuityExpect: A low reading, a few ohms or less, at every box on the same cable run.
- Open (OL) at some boxesBroken interconnect conductor
- Continuous everywhereAn alarm isn’t sending or receiving
- All but oneDoes that one alarm sound when you press its own test button?
- No, silentAlarm doesn’t sound at all
- Yes, but not with the othersAre all the alarms the same brand, or listed as compatible with each other?
- Mixed or unknown brandsIncompatible alarms
- All the same brand or listed compatibleTest: Inspect the interconnect at each box
- Loose, capped or missing interconnectInterconnect not connected at a box
- All connectedTest: Test the interconnect wire for continuityExpect: A low reading, a few ohms or less, at every box on the same cable run.
- Open (OL) at some boxesBroken interconnect conductor
- Continuous everywhereAn alarm isn’t sending or receiving
- None of the othersAre all the alarms the same brand, or listed as compatible with each other?