Fire Alarm T Taps
- Thread starter moresi
- Start date
- Status
peter d
Senior Member
- Location
- New England
Make sure the manufacturer of the FACP allows it, and make sure you local codes allow it.
T-tapping is strictly forbidden by local codes in my area.
T-tapping is strictly forbidden by local codes in my area.
Security101
Senior Member
- Location
- Northern Indiana
Peter, If I may ask - what do they allow - only home runs?
Do they allow properly marked/labeled T Tapping in junction boxes?
I've never run into a problem - as long as the FACP was designed for it...
Jim
peter d
Senior Member
- Location
- New England
Only a Class A loop is allowed. No T-tapping of any kind is allowed under any circumstances. If you need to add a device you have to interrupt the look somewhere to insert a device.
Class B loops are also allowed for local (not monitored or municipally connected) but they must be wired like a Class A system with the EOL resistors terminating back in the FACP on a terminal block as opposed to the last device.
quogueelectric
Senior Member
- Location
- new york
T taps are ALLWAYS a bad idea. When a fa system is wired according to the blueprint in a class A fashion it is much easier to troubleshoot and maintain when you know exactly how it was wired. When you work for a large company you cannot wire everything yourself and when someone screws up it is a breeze to fix but when you have t taps all over the place it is just a lesser quality job.
TOOL_5150
Senior Member
- Location
- bay area, ca
I have never done Fire alarm stuff... What is a T Tap?
~Matt
~Matt
quogueelectric
Senior Member
- Location
- new york
A class A fa system has say up to 99 devices on a loop smokes for example. It used to matter in and out of the bases more years ago. Start at device 1 go to 2 go to 3 ect......ect.......... to 99 then back to the facp panel with an eol resistor located in the panel. One big numerically sequenced loop. Modern day electronics hae addressable devices which are not just a mechanical switch yet an interactive addressable network of heads who report through a network address instyead of a switch. The computer checks addresable heads one at a time from the main computer. Hello device 1 are you there... device 1 says yes I am here.....Ok device 1 are you in alarm? No I am not in alarm..... OK device 2 are you there? Yes I am there ..Ok device 2 are you in alarm?? ect ect through 99 . Now these devices do not have to be wired in a big series loop because they are on a parallel network . A t tap is just a wiring point in parallel instead of series. Like if you wired device 76 in between device 4 and 5 . It will work but is much more difficult to troubleshoot with t taps all over the place.
Security101
Senior Member
- Location
- Northern Indiana
Most definitely a class A circuit is a better option and provides more redundancy, but class B's are the norm around here, depending on occupancy of course. (mostly an industrial area)
We always print our runs, taps, devices, etc completely and accurately so service is not an issue. And we only do this (class b's) with addressable systems - so if there's a failure - we don't have to hunt it down - we know where it is...
Some of our class B runs will terminate in the can and may be connected in a partial class A fashion anyway...
Jim
We always print our runs, taps, devices, etc completely and accurately so service is not an issue. And we only do this (class b's) with addressable systems - so if there's a failure - we don't have to hunt it down - we know where it is...
Some of our class B runs will terminate in the can and may be connected in a partial class A fashion anyway...
Jim
Last edited:
quogueelectric
Senior Member
- Location
- new york
Whether class a or b I find following the print is the key to a quality install. Knowing where the cabling routes are is crucial to expansion /troubleshooting/maintenance. I have seen many fa jobs belly up because of a simple skinned wire and untrained fa people panicking on the troubleshoot. Just take a deep breath and say this is usually something very simple. Use your troubleshooting skills and find it in a quick orderly fashion. A clearly drawn asbuilt is awesome to troubleshoot and seldomly available. All information is a plus.
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
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
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.
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
Senior Member
- Location
- Northern Indiana
Wire nuts, terminal strip or solder...
Jim
Jim
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
Member
Proper T-Tap
Proper T-Tap
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).
Proper T-Tap
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).
n1hampton
Member
- Location
- Indianapolis
In short, T tapping prevents proper supervision of a circuit. You can disconect a device and not show a trouble. It does not matter how long the tap is. In all the books it clearly staes that the device must show a trouble condition when removed. This does not apply to addresable systems unless specified by manufacture or the AHJ.
like others said, if its the addressable portion of a system, "class A" doesn't always apply (supervision is achieved, but not necessarily survivability depending on the system) (subject to ahj approval), and a lot of manufacturers allow T taps, although excessive use of them does not make for a good installation (causes slow mapping). we use wirenuts.
Last edited:
The OP stated T taps on a SLC, they are fine, on a class B loop.
I would add a loop isolation module, personally.
Security101
Senior Member
- Location
- Northern Indiana
- Status