Wire Supervision/ t-tapping

akbrtrdr

Member
Location
Alaska
Seems like i read in the code at some point there are instances where alarm wiring does not need to be supervised such as a run under 3 feet long. I was also told by an engineer t-tapping on a conventional system is allowed if the device being tapped is within 5' of the tap. Can anyone confirm or dispute this?
Thanks
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Seems like i read in the code at some point there are instances where alarm wiring does not need to be supervised such as a run under 3 feet long. I was also told by an engineer t-tapping on a conventional system is allowed if the device being tapped is within 5' of the tap. Can anyone confirm or dispute this?
Thanks
The 3-foot rule is generally for the location of a control or relay module used for interacting with 3rd party systems such as fire/smoke dampers and elevator controllers. This is because usually the dry contact output is unsupervised, so the code folks said 3 feet was close enough. Per NFPA 72-2016:

21.2.4* Emergency control function interface devices shall be
located within 3 ft (1 m) of the component controlling the
emergency control function.


For T-taps, there is no slack as far as conventional systems are concerned. If you T-tap, which ever branch doesn't contain a resistor is not supervised. There is one conventional panel I've run into that allows you to T-tap, once. It was the FCI-72, IIRC.
 

kwired

Electron manager
Location
NE Nebraska
The 3-foot rule is generally for the location of a control or relay module used for interacting with 3rd party systems such as fire/smoke dampers and elevator controllers. This is because usually the dry contact output is unsupervised, so the code folks said 3 feet was close enough. Per NFPA 72-2016:

21.2.4* Emergency control function interface devices shall be
located within 3 ft (1 m) of the component controlling the
emergency control function.


For T-taps, there is no slack as far as conventional systems are concerned. If you T-tap, which ever branch doesn't contain a resistor is not supervised. There is one conventional panel I've run into that allows you to T-tap, once. It was the FCI-72, IIRC.
Doesn't matter if the branch is 1 foot or 1000 feet long either.

I don't work on this kind of thing hardly at all, but would think addressable components can possibly change the rules a little. If an addressed object stops communicating it can cause a trouble alert.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Doesn't matter if the branch is 1 foot or 1000 feet long either.

I don't work on this kind of thing hardly at all, but would think addressable components can possibly change the rules a little. If an addressed object stops communicating it can cause a trouble alert.
Yes, that is true. For Class B systems, the signal line circuit (SLC) may be T-tapped. However, for Class A SLC's and all notification appliance circuits, T-tapping is not allowed.
 
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