The short answer
Fire alarm line replacement swaps the copper lines feeding a DACT for supervised cellular or fiber transport. The panel keeps its programming and keeps dialing the central station, while the transport path is monitored continuously so a failure is annunciated rather than discovered at the next inspection.
Why the two-copper-line design existed
Legacy DACT installations used two separate copper lines so a single line failure would not silence the panel. Both lines were supervised by the panel itself, which reported a trouble condition if dial tone disappeared.
That redundancy assumption breaks when both lines ride the same aging copper facility, which they usually do.
What supervision means now
- Continuous verification that the analog port has dial tone
- Continuous verification that the cellular or fiber path is up
- Automatic failover between carriers or between cellular and wired transport
- Alerting to your team and to the monitoring provider, with retained history
Cutover sequence
- Place the account on test with the central station
- Connect the DACT to the managed box and confirm dial tone
- Run signal tests for every zone type through to the receiver
- Verify trouble reporting by simulating a path failure
- Take the account off test and document results
- Release copper only after documented success
Coordinating with the AHJ
NFPA 72 permits multiple communication technologies for alarm transmission, with specific supervision and reporting expectations. The safest path is to supply the AHJ with the installed configuration, the supervision method, and the test record before the annual inspection rather than during it.
Last updated 2026-08-20.