Douglas Krantz - Technical Writer - Describing How It Works
Get the Book Make It Work - Convetional Fire Alarms
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How do I Fix this Comm Fail Light?

Comm Fail means that something went wrong with the fire alarm communications between the fire panel and the monitoring company. The first test to make is to use your butt set and listen to the phone lines as the panel is trying to make contact.

The Comm Fail light on the panel means that communications failed somewhere between the panel and the monitoring company.

Greetings Douglas,

Can you tell me on the secondary phone line why the Comm Fail light (amber color) is on and how do I fix?

Thank you, SR

Phone Sec - Comm Fail means that the Communications Failed to complete the last time the Secondary Telephone Line was tested by the panel.

If it stays on for more than two days, it could mean:
  • The Comm Fail circuitry is somehow latched on (it's holding on to the fact that it is in trouble and won't try again until the trouble is gone) and needs to be forced to try again
  • The fire alarm panel can't get through on the Secondary Telephone Line every time the panel tests the phone line

To force it to try again, listen to the secondary phone line using your butt set, disconnect the primary telephone line and wait for the message to be sent on the secondary telephone line.

Listen to the Phone Lines

The only way to tell what is happening on the telephone lines is to listen to them. Use your butt-set as a test tool to hear exactly what is happening. (Make sure the microphone on you butt-set isn't picking up any room sound, or your voice. Extra sound from your butt-set microphone may mess up the fire alarm communicator's signals.)

Just listening to what is happening can help you understand what is wrong. The sequence is:
  1. Silence - Before any signal is sent
  2. Dial Tone - The panel has "picked up the phone" (using a relay, the panel electronically takes the handset of the telephone "Off Hook"). Once the local telephone is Off-Hook, the phone company sends a dial tone back to the panel
  3. Dialing Touch Tones - The panel is "dialing the number"
  4. Hand-Shake Tones - The monitoring company's receiver has answered the phone and sends a series of short tones asking "What Language Are You Using?" - languages like SIA, 4+2, Contact ID, Etc. After the panel hears the correct handshake tones, the panel sends the message
  5. Message - The panel sends information including account number, what kind of signal it's sending, and whether it's an activation or restore. - This message could be just noise like SIA signals, a series of short, rapid tones like 4+2, a series of touch tones like Contact ID, Etc.
  6. Kiss-Off Tone - The monitoring company's receiver confirms to the local panel that it received the signal
  7. Silence - Both phones have hung up - Even be aware of this hanging up. Failure of the panel to hang up means that the phone company won't send another dial tone.

Comm Fail means that the panel has not heard the Kiss-Off signal; the panel thinks that the communications have failed, somewhere in the sequence of communication.

There are many places in the system that could be the problem. Listening to the telephone lines using your butt set will at least show you where to start looking.

Douglas Krantz
See how Class A Wiring works


facpdoug@douglaskrantz.com
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