Edwards QS4 Fire Alarm System

[Hertz Electric]

I`m working on an edwards qs4 fire alarm system. I`ve got an addressible loop going around the building, 2 wires going and 2 wires returning to the panel. Is it okay to tap the loop and run two wires down to an addressible pull station, but not run 2 wires back. I`m told t-taps are okay with this system. But is what I described above what a t-tap is called. Thanks for any help.

 

[peter d]

I believe T-tapping may be acceptable on an addressable system. You must check your local codes as well as the manufacturers recomendations.

 

[ron]

The national code does not require a class A circuit (2 wire there and back) (your local code may differ), but if your system is designed as class A, then you must install two there and two back.

 

[Smart $]

...But is what I described above what a t-tap is called.

Yes.

I concur with the other responses.

However, I have never seen a "loop" that returns to the panel, but I'm far from an expert, and have never worked with Edwards equipment. My experiences have been with Simplex/Grinnell and Notifier systems, and very limited at that.

As I understand it, Class A wiring, the kind you cannot T-tap, typically utilizes an End Of Line Resistor connected across the end of the two leads, at the last device in the circuit, so the panel can place on and monitor a current through the loop. The panel will indicate a fault should that current drop to zero (open circuit) or become too high (short circuit).

I believe Class A wiring is typically used on loops having non-addressable devices. In the case of addressable-device loops, the panel will indicate a fault if the device fails to respond to a status check, which is performed at short and regular intervals ...so a circuit-checking current is not necessary.

 

[ron]

Class A circuits do not use an EOL resister, but the end of the circuit actually returns to the control panel to offer another path for communications.

 

[Smart $]

Class A circuits do not use an EOL resister, but the end of the circuit actually returns to the control panel to offer another path for communications.

You are correct (more info).

So barring local prohibitions, under what condiitons can one t-tap a fire alarm system circuit? Is it only permitted if so noted in the manufacturer's instructions?

 

[leecordochorea]

Hertz, is the card to which the loop is connected a "SLIC" card (with loop connecte to lower right "LOOP" of skinny card) or a "ZA8-2? card (with loop connected to upper left "ZONE" of not-so-skinny card)? If it's a ZA8-2 (Class A Style 6), then don't use an addressable pull station and don't t-tap. If it's a SLIC (Class A Style 7), then use an addressable pull station and refer to page A.3 through A.7 of the QS4 Technical Manual to insure you've not exceeded allowable loop length.

 

[jbroccoli]

Hertz,
On an addressable fire alarm system, a SLC (data loop or initiating loop) wire pair leaving the panel and then returning to the panel constitutes a Style 6 loop. Having send and return wires allows for system operation around a single wire break. While T tapping a device into this wiring configuration may work, the system will not continue to provide this same style of function. Additionally, most current EST panels incorporate a mapping function which will indicate a panel trouble "line card mapping fault" if a device is located incorrectly (based upon original system programming) in the SLC loop.

On addressable fire alarm systems no SLC (signaling line circuit - this is the data line that initiating and control devices connect to) utilizes an EOL device. Circuit integrity in monitored by polling each device and ensuring that all programmed devices respond properly. A style 4 SLC circuit consists of a SLC wire pair leaving the panel with no return. T Tapping is permitted in this type configuration.