Reference · Testing & Inspection
Trouble Signal
A signal indicating a fault in the system or its pathways: open circuit, ground fault, low battery, loss of AC power, communication failure. Must be indicated within 200 seconds and is distinct from alarm and supervisory signals.
NFPA 72: 10.15
Section numbers vary by edition — confirm in the edition your AHJ has adopted.
Read more in these guides
NFPA 72 Explained for BeginnersNFPA 72 is the common language of the fire alarm industry. Here's a plain-language overview of what it is and how to use it responsibly.Commercial Fire Alarm Troubleshooting: Opens, Shorts & Ground FaultsTrouble signals on a commercial system almost always come down to opens, shorts, or ground faults. Here's a repeatable way to isolate them without guesswork.