14.2 Transmission Paths & 90-Second Alarm Window

14.2 Transmission Paths & 90-Second Alarm Window

Quick Answer: Off-premises alarm signals must reach the supervising station within the Chapter 26 performance window—commonly tested as 90 seconds from initiation at the protected premises for DACT-class and many related technologies. Paths must be supervised (with periodic test signals—often discussed on a 24-hour cycle for classic dual-line DACT practice). Historical DACTs used two phone lines; modern IP/cellular/mesh listed communicators may be single-path or dual-path under performance rules. A failed path that is not troubleshot is a monitoring failure even when local notification still works.

Section 14.1 named the service types. This section is the wire, radio, and timer layer: how the signal leaves the building and how code measures success.

The Performance Question Level II Must Answer

When a smoke detector or waterflow switch initiates a fire alarm, two clocks matter:

1. Local clock: How fast does the premises system annunciate and notify occupants / control outputs?
2. Off-premises clock: How fast does the alarm signal arrive at the supervising station?

Chapter 26 transmission requirements target that second clock. A frequent exam anchor:

Maximum time between a fire alarm initiating event at the protected premises and arrival of the alarm signal at the supervising station for a DACT (and the same 90-second performance idea applied broadly in Chapter 26 transmission rules) is 90 seconds.

Memorize the triad: alarm → supervising station → 90 seconds (for the technologies and stems that cite that limit). Do not confuse it with:

• Detector response time to smoke in a room
• NAC temporal pattern timing
• Battery 24-hour standby duration (power, not transmission)
• Monthly/annual ITM intervals

Scenario: A tech tests a pull station; horns sound in 2 seconds. The monitoring center log shows the alarm account event 4 minutes later because the primary cellular path was down and retry logic stalled. Local test “passed” emotionally; Chapter 26 transmission performance failed. Acceptance and periodic tests must exercise the off-premises path, not only the NAC.

Historical DACT Dual-Phone-Line Model

A digital alarm communicator transmitter (DACT) is the classic dialer: premises equipment seizes telephone lines and sends digital signals to a digital alarm communicator receiver (DACR) at the station.

Dual-line concept

Traditional NFPA 72 DACT practice required two telephone lines (or approved equivalent dual means) so a single cut line would not silently kill monitoring. Level II still sees dual-line DACTs on existing buildings and on some new installs where copper remains.

Minimum line count exam anchor: Historical DACT telephone-line minimum is two lines—not one “because the panel is smart.”

Path integrity testing (24-hour concept)

Each communications path used by DACT-style dual-line arrangements must be tested for integrity on a frequent automatic cycle. Exam and field language commonly anchors this at at least every 24 hours per path, with failure producing a trouble signal (at premises and/or as required toward the station per the rules for that technology).

Level II implications:

• A path that has not checked in is not “probably fine”
• After phone-system changes (VoIP conversions, PBX reprogramming, disconnected jacks), expect path troubles even if analog handsets still “have dial tone” somewhere else in the building
• Document which pairs/jacks are the fire alarm paths—facilities painters love to unplug “extra” lines

Trap: Assuming a single shared tenant phone line is an acceptable sole DACT path on a dual-line design. It is not a complete dual-path DACT arrangement.

Modern Listed Communicators: IP, Cellular, Mesh

Copper PSTN lines are disappearing. Industry and NFPA 72 evolved toward performance-based transmission using listed communicators:

Single-path vs dual-path awareness

Chapter 26 allows different architectures when performance, supervision, and listing requirements are met. Level II awareness—not full design PE depth:

• Dual-path systems use two independent communications methods so a single infrastructure failure (one carrier, one ISP) is less likely to kill monitoring silently
• Single-path systems may be permitted when the technology and standard’s performance/supervision criteria for single-path operation are met (often with more stringent check-in/supervision expectations than casual “set and forget”)
• Never assume “one SIM card forever” equals code compliance without reading the listed communicator’s application and the project specification

Scenario: IT renumbers VLANs and blocks outbound ports used by the fire IP communicator. Local FACU shows normal; supervising station loses check-ins and eventually reports communications failure. Level II lesson: network changes are fire alarm changes when IP is the path—coordinate and retest.

Path Supervision and Trouble on Failure

Supervision answers: “Is the path still capable of delivering signals?” Mechanisms vary by technology:

• Periodic test/check-in signals from premises to station
• Station-side timers that declare failure if check-ins stop
• Premises trouble annunciation when the communicator cannot reach the station or loses a required path
• Dual-path systems that trouble on loss of one path even if the other still works (so the redundancy is real, not decorative)

When a required path fails:

1. A trouble condition is expected (premises indication and/or station notification per the system rules)
2. The impairment/response process may apply if monitoring is compromised (Ch 8 impairment themes—notify supervising station/AHJ as required)
3. Repair and retest of transmission, not only “reset panel”

Do not confuse signal types:

A communications failure is usually a trouble (or specific comm-fail event), not a fire alarm. Training station operators and SOO authors to keep those categories straight prevents wrong dispatch—and wrong exam answers.

What Drawings and Notes Must Capture

For submittal/layout quality:

1. Technology named: DACT dual-line, dual-path IP/cellular, etc.
2. Path count/intent: Single-path performance design vs dual-path
3. Physical terminations: Phone board pairs, network jack IDs, antenna
4. Power source for communicator (FACU-powered vs separate supply) coordinated with battery calcs
5. SOO rows for alarm/supervisory/trouble transmission and path trouble
6. Test method notes: How 90-second delivery and path tests will be demonstrated at acceptance

Weak note: “Monitoring by others.” Stronger note: “Dual-path listed communicator; primary Ethernet circuit FA-NET-1; secondary cellular; alarm delivery to supervising station within 90 seconds; path supervision per manufacturer listing and NFPA 72 Chapter 26; path loss = trouble."

Field Failure Patterns Level II Should Anticipate

Exam Focus

Lock these anchors:

• 90 seconds — alarm signal arrival at supervising station (DACT / Chapter 26 transmission performance stems)
• Two lines — traditional DACT telephone minimum
• 24-hour — classic path integrity test interval language for dual-line DACT-style paths
• Trouble — expected when a required path fails
• Single vs dual path — modern listed systems follow performance/listing rules; dual infrastructure is the diversity idea, not two labels on one fragile link

Prefer answers that time alarm delivery, supervise paths, and reject “horns worked, so monitoring must be fine.” Section 14.3 assigns who generates signals locally versus who retransmits them at the station.