Fire Alarm T Taps

[moresi]

I agree with the T tap info. that all have provided and also that a good plan is the key to a successful install. I am curious as to how techs. are actually making the T taps. I have seen some installs where simple splicing and wire nut connections have been made opposed to a real "t tap" as defined in wire splicing manuals. My question is how are you physically making the T tap splice / connection?

[LarryFine]

I've been under the impression that this is about adding a new sensor to an existing system with an end-of-the-line resistor for line supervision. If you merely tee the new branch in, the added branch won't be supervised.

I've always run four conductors to the new device, opened the pair, connected two wires from the panel side of the break to the new device, and the other two back to the downstream end toward, the resistor.

[Security101]

Wire nuts, terminal strip or solder...

Jim

[moresi]

Was going along the lines of an addressable system that permits T tapping for SLC wire runs. Was curious how these "taps" were being made. Yes - when a zoned system which uses EOLR's is installed I too will run a 4 wire to additional devices to maintain the continous loop.

[nhfire77]

Originally Posted by moresi

Was going along the lines of an addressable system that permits T tapping for SLC wire runs. Was curious how these "taps" were being made. Yes - when a zoned system which uses EOLR's is installed I too will run a 4 wire to additional devices to maintain the continuous loop.

I would go to the closest device and pull a 16/4 or 14/4 to maintain a continous circuit. Even though the circuit its the same cable it helps with troubleshooting because there are not true taps.

If, I were to just run 2 conductors, you can just wire nut it in a J box or at a device. You can cut it in any way you want, but its still a hack job.


Of course SLC isolators would be safer, and more profitable Never leave the bid without one.

[GE_Vigilant_SC]

At a minimum, always follow the manufacturer's installation documentation and the approved system design. "T-taps", the how-to's and maximum number of, is typically outlined in most major manufacturer's fire alarm installation manuals as this is critical in calculating the overall loading and distance of the addressable SLC (Signaling Line Circuit). As the number of T-taps increase, so does the amount of circuit capacitance and impedance. As SLC impedance and/or capacitance increases, circuit loading capacity and maximum allowable circuit length decreases. This directly impacts field device voltages and communication between the field device and the control unit.

One more thing to remember is that a "T-tap" is defined as such because when a new branch circuit is spliced into an existing branch, it forms a capital
"T" when shown on a schematic drawing (branch circuit direction is typically shown perpendicular to existing circuit direction). Also note that the junction formed by a "T-tap" has three conductors- no more, no less. This means that more than three conductors junctioned at any one point is NOT a "T-tap" (these multi-conductor junctions are sometimes referred to as "star-taps" or "spider-taps"). While not necessarily prohibited in some manufacturers' system documentation, they are not necessarily encouraged either.

In the past, I've used listed junctions (wire nuts, terminal strips) and listed enclosures (junction boxes) to splice (T-tap) the SLC, where approved. In addition to observing the approved design (and tolerances) & manufacturer's installation documentation, accurate documentation of any field changes to the original design is paramount to ensure that the system will work as intended. So, make sure your as-built drawings are as detailed as possible!

Lastly, some manufacturers' equipment will produce "visual as-built schematics" of the SLC when used in conjunction with their executive software and a PC. This feature allows quick verification of the SLC circuit installation by showing the pathway (wiring) relationship of each device to one another, including all branches (T-taps).