Fire Alarm Phone Line
Trouble Alarm Tech
Alarm Panel Keeps Going Into
Telephone Line Trouble!"
I hear that complaint all the time.
There's a lot of confusion about what causes that trouble alarm. This
Tech Bulletin should explain it.
The Fire Alarm Panel throws a Telephone
Line Trouble Alarm several times a day.
The customer decided to share the phone
line(s) for the Fire Alarm Panel with the regular phone lines used at
the business. Depending on the particular type of fire alarm, there may
be one or two lines.
When the engineers designed the fire
alarm panel they assumed you would have dedicated phone lines, as I
believe is required for a UL Listed Fire Alarm (usually required in
hotels and places where there are a lot of people that can get killed in
For whatever reason, most of the
engineers seem to have chosen about 5 volts as the trigger threshold for
the telephone alarm fault. Since nothing in electronics is exact,
including the meter you read the voltage with, the phone line trouble
alarm could get triggered by 4 volts or 6 volts.
The problem only
occurs when someone goes off-hook to talk on the phone line that's
being shared with the fire alarm panel.
Want to get rid of the problem right
away? Stop sharing the phone line with
the alarm panel!
People think I'm an idiot when I tell
them that since everybody is looking to save as much money as possible.
Saving money is always good when it makes sense, but screwing around
with the fire alarm, doing something you're not supposed to do, can put
your company out of business when a fire breaks out and someone gets
hurt. There are a lot of lawyers out there just looking for something to do.
When you go off-hook on a phone line,
the voltage drops from maybe 48VDC, to 4 to 18VDC, depending on the loop
current (how far the premise is from the phone company's central office
- the CO). If you're pretty close, the loop current will be over 30ma, and
the voltage will be over 6VDC. If you're farther away from the CO, the
loop current can be as low as 23ma, and the off-hook voltage could be
When nobody's talking on the shared
phone line, the voltage is 48VDC, and there's no phone line trouble
alarm. When somebody's talking on the phone line, the voltage drops to
below 5 to 6VDC at some premises, triggering the phone line trouble
alarm when it decides to do it's regular testing while a voice call is in progress. It's that simple.
The fire alarm panel doesn't throw a telephone line fault
alarm when it's going off-hook to make a test call or
report a fire because it's not checking for the voltage then - it's
just trying to make the call.
It only checks the voltage of the
phone line when the alarm panel is idle, at whatever frequency the
engineers designed into it (every 5 minutes?). When the alarm
panel goes off-hook, it automatically disconnects any phones connected
behind the RJ31X jack. By the way, you
must have an RJ31X jack if you're going to share the
lines with an alarm system. The RJ31X allows the alarm panel to
disconnect the phones from the line when it's trying to make a call so
the line won't be busy - even if a phone is accidentally left off-hook.
Again, if you don't share the fire
alarm's phone lines with your phone system and try to talk on them, you
won't see the phone line trouble alarms.
OK. So you need to save the money and
humans are infinitely replaceable.
All you have to do is something to prevent the off-hook voltage on the
phone line from dropping below 6VDC (or so) while you're talking on it.
After trying to boost the
loop current and off-hook talk battery, our engineer came up with a much
better/easier/cheaper solution. It turns out that our Loop Current
Regulatorô will drop the off-hook voltage by 6 volts if you put it
in-front of all the phones.
That means that if the normal off-hook
voltage is 4VDC while talking on that line, and you put the Loop
Current Regulatorô in-front of all the phones
(or the phone system), but not in-front of the alarm
system (from the phone company CO), the fire alarm panel will see 10VDC
when you're talking on the phone... which is over the threshold to
trigger the phone line trouble alarm (6V), so you will never see
that fault alarm again.
If you don't understand this, there's not much else I can say (please
don't call me!). Just put a Loop Current Regulatorô in-front
of the phones, but not on the pair going into the RJ31X
from the phone company. If you don't know what an RJ31X is and how it's
wired, you definitely shouldn't be messing with this stuff.
1 Line Loop Current Regulatorô
Has an RJ-11 in and out
2 Line Loop Current Regulatorô
Has an RJ-14 in and out (both lines on the same modular jack/plug),
which may be harder to install
than two 1 Line Regulators, but
1 Line Regulators.
Wondering why you're seeing this
The alarm panel engineers could just as easily
have chosen 2 volts, and you wouldn't be seeing this problem - but they
didn't know just how driven people would be to save money these days
when they designed the alarm panel.
Since fire alarm
panels are tested and approved by UL, no changes can be made on them
after they're UL tested without the alarm manufacturer paying UL big
bucks to retest the panel. Not a trivial task for a fairly complex gizmo
that's made to save lives and property.
This isn't the only
telephone problem I hear a lot
with both fire and
burglar alarm systems.
With the advent of VoIP phone lines that are a lot
cheaper than real phone lines from the real phone company, a lot of
customers wake up one day and decide to save money by switching to VoIP
phone lines - or maybe buy a T1 from some salesman that's convinced them
they can save big bucks.
The customer doesn't even consider that they use phone lines for
other things than voice - like faxes, modems, credit card machines,
automation systems and
fire/burglar alarms. VoIP phone companies tell them that they're a
phone company, and the customer believes it... because they figure every
phone company has the same kind of phone lines. Cheaper ones are just
The VoIP or T1 salesman doesn't tell you the
shortcomings of what they're selling. They don't have to until you ask -
and you have no idea what to ask until you've gone through this and have
experienced the problems yourself.
Even if your real phone company or phone system vendor
told you what could happen, you wouldn't believe them anyway. Most of us
have to learn the hard way.
So a short time after the new lines are installed, either
VoIP lines, cable company phone lines, a T1, or CLEC (Competitive Phone
Company) phone lines, you get to see the problems first hand.
Maybe you don't find out until you go to set the alarm
and it throws a communications error because it can't call your alarm
company (if you have openings and closings).
Maybe you'll find out when you come in in the morning,
and the alarm says something like "Communications Error," which occurred
when the alarm tried to make a test call at midnight. About that time
your alarm company will call you to tell you they didn't receive the
test call last night. Then you start to sweat.
You already had the real phone lines disconnected.
There's no going back easily, cheaply or quickly. You call your phone
system vendor. You call your alarm company. They laugh at you because
it's the third call they've gotten like this, this week.
At that point whatever happens you'll be paying T&M for
someone to try to straighten this mess out for you. And you thought you
were going to save money?