Re: Napco MA3000 - Dialer Test on both Lines?

[Nomen Nescio <nobody@xxxxxxxxx>]

Bass said:

>> But suppose line 2 is bad?
>
>Have you forgotten what I said earlier about running a third relay to preven
>shorting line 1 if there is a pre-existing trouble condition?
>
>> More importantly, if line 2 really is
>> inoperative and you short out line 1...
>
>See above.  It really helps if you know the panel before evaluating someone
>else's methods.

Oh, I didn't forget.  However, it appears that you do not understand why
the code was changed to require transmission of test signals over both
lines, instead of just depending on the telephone line monitors.

Commercial fire alarm communicators have always required two phone lines
and telephone line monitors.  This has been a requirement since they were
first introduced in the early 1980s.   Back in those days, when the phone
company disconnected a phone number, it often meant someone physically
disconnected wires at the telco central office.  That would trip the phone
line monitor in the fire alarm panel, annunciate the trouble, and transmit
a trouble signal over the other phone line.

Today, telephone numbers are often disconnected via software, rather than
by disconnecting wires.  This means the phone line still has voltage on it,
but cannot draw dial tone.  The phone line monitor doesn't detect this
problem.

So, consider a fire alarm panel set up as you propose.  Somehow, line 2
gets turned off, but without loss of voltage.  Perhaps the customer
cancelled a phone number he did not recognize, or perhaps the phone company
turned off the wrong line.  Test time arrives, and your relay shorts out
line 1.  Since the panel hasn't detected a phone line trouble, your trouble
relay does not prevent this from happening.

The panel tries to dial out on line 1 and fails.  The panel then tries to
dial out on line 2 and fails.  The panel alternates between these two lines
until the maximum number of dialing attempts is reached, or until your
phone line shorting relay times out and releases line 1.

During the time line 1 is intentionally shorted, the fire alarm panel will
be unable to transmit an alarm signal.  That could be fifteen minutes or
so, figuring eight dialing attempts per line.

On the other hand, if you program the phone line shorting relay to restore
in a minute or two, then the test signal will be transmitted over the
primary phone line when that relay releases.  The control panel will not
perceive this as a trouble condition.  It will just think it had to make a
few extra dialing attempts.  The problem on line 2 goes undetected.

Sorry, but this just doesn't fly.  Either the system is temporarily
disabled, or the phone line trouble goes undetected.

- badenov