T-Tapping Question

I was wondering what the true definition of T-Tapping is. Only branching off once to another area or device? Tying several wires together all going to different areas or devices? The reason I ask I have electricians running my FPLP wire for me now for fire alarm and they seem to want to just branch off to each SLC device. My panel allows for T-Tapping(If what they are is even considered that) but I've never done it this way before and really don't care for it. I will Tap if they add a device later or if I'm going between floors but never tie several wires(as many as 8 that I've seen) together each headed to different devices...Just the way I was taught.

Thanks for any replies


PS: Great forum BTW
 

iwire

Moderator
Staff member
Location
Massachusetts
In some cases it is allowed but I think it is a crappy way to go. Troubleshooting it later would be a pain in the neck.
 

ISSLDR

Member
T-TAP

T-TAP

If the panel allows multiplexing and the devices being added has a serial number or uses a multiplexer requiring a serial number it works okay. We use a system that allows a polling loop and you can T-TAP or STAR as long as the devices added use a serial number for tracing the device.
 

Strathead

Senior Member
T-tapping is basically what you envision. It is easier to see on paper, and it doesn't really matter how many devices it goes off to. The opposite of T-tapping is the term more people have a problem with. I more often than not hear it called parallel. It is devices wired in "tandem". Your aversion to T-tapping is akin to, call it, the arrogance of electricians every time something new comes out. Most of us have similar aversions. I, for example, just can't imagine running conduit without pulling a ground wire. iWire is incorrect about troubleshooting, because a fire alarm system that allows T-tapping has addressable devices, Therefor each device "talks" to the panel. You could really, just as easily claim the installation is better because a wiring failure will usually result in fewer devices being off line until repairs are made. Many engineers still require tandem wiring regardless of the addressable nature of devices, but there really is nothing wrong with it.
 

iwire

Moderator
Staff member
Location
Massachusetts
iWire is incorrect about troubleshooting, because a fire alarm system that allows T-tapping has addressable devices, Therefor each device "talks" to the panel. You could really, just as easily claim the installation is better because a wiring failure will usually result in fewer devices being off line until repairs are made. Many engineers still require tandem wiring regardless of the addressable nature of devices, but there really is nothing wrong with it.
Strange, I have been a successful fire alarm installer and troubeshooter yet I still find t tapping a poor way to go and feel it makes troubleshooting harder unless you have great as builts to work from

I am very happy that most of our job specs prohibit t tapping fire alarm circuits.
 

Strathead

Senior Member
Strange, I have been a successful fire alarm installer and troubeshooter yet I still find t tapping a poor way to go and feel it makes troubleshooting harder unless you have great as builts to work from

I am very happy that most of our job specs prohibit t tapping fire alarm circuits.
The exact same as-built argument applies for tandem wiring. I like tandem wiring better also, but I know it is just because I am an old hand. Even still, a properly installed system is a properly installed system regardless of how it is installed.

Here is an example of t-tapping being better than tandem, that I just did. I have a Historic building it was about 200 feet long, three stories and an attic. It was split in to five distinct risers with a 4 hour wall dividing each. the conduit had to be run in the crawl space the up to each floor of a section. This is a new Simplex addressable NAC. I set a terminal box at the main panel. I brought a NAC circuit pair and an IDnet pair out in dedicated conduit to each wing. I then ran through devices to the attic in each wing. You can't tell me that T-tap wiring is harder to troubleshoot than had I carried a pair of wires from the attic back down three floors, through the crawl space and up to the next wing. I can isolate each wing right from the main panel. (The University was quite impressed)
 

jeffcmag

Member
T-Tapping, good or bad?

T-Tapping, good or bad?

IMHO T-tapping is not a good way to wire installations. Although it is acceptable on addressable circuits using style 4 wiring only, it is bad practice in as much as if there is a short on a t-tapped line it will bring the SLC circuit down with no direct way to locate the trouble except to open every device in on the shorted line until you find the tapped line that is shorted. There are cases where it is necessary (cost prohibitive) or later additions that will bring the wire length over the limit, but it should not be done without sustainable documentation (permanent marking of the JB or device box with the t-tap) and should have isolation modules at each tapped branch to protect the system from shorts on a particular tapped line.

To me, the only acceptable T-tap would be if you have a relay module fed from a duct detector to shut down the AHU, as the t-tap is dedicated to a particular device only and not a long wire length.

Once an installation is completed there is no telling where the t-taps are without as built drawings or excellent documentation. Even with those it makes troubleshooting overly difficult and labor intensive which in the long run creates more problems than it solves.
 
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