T-Tapping in Fire Loop Line

 T-Tapping in Fire Loop Line

A fire alarm “T-Tap” is merely a parallel tap into the loop. The reason T-Tap wiring is allowed is because communications are being supervised to the device level. T-Tapping the different legs of the SLC provide multiple communications paths of the field devices and control equipment.
The answer to the question of how many T-Taps is allowed --- is "It Depends". It depends on the manufacturer and it depends on how easy the installer wants to make the system for the technician when servicing the system for the coming years. On a conventional system “T-Tap” not working.

Style 4 wiring (somewhat similar to Class B wiring), which is the data-loop or signaling line circuit (SLC), allows an unlimited number of T-Taps, at least for most manufacturers. Signaling Line Circuit (SLC), carries signals in the form of data between the panel and the input and output devices. Canada calls "Class B Level 1" "Data Communications Link (DCL) Style B". Someone called Initiating Device Circuit (IDC), its carries signals from the input devices to the panel.

Field Devices Connected to an SLC/DCL/IDC.

Input

·        Smoke Detectors

·        Heat Detectors

·        Combination Smoke/Heat Detectors

·        Pull Stations

·        Alarm and Supervisory Input Modules

Output

·        Control Relays

·        NAC Riser Modules

o   24 VDC Audible

o   24 VDC Visible

o   24 VDC Combination Audible/Visible

o   Audio for Speakers (Direct Current (DC) blocking capacitor allows 70.7 VAC 200-20KHz through) independent of other audio.

o   Firefighter’s Phone

Every device on a Signaling Line Circuit is a T-Tap for the Panel.

 
Long Star-Taps

Most fire alarm systems that use Style 4 wiring for the SLC are electronically connecting every device directly to the terminals of the fire alarm panel. Being wire nutted at all junctions, electrically the wire loop is a single pair of copper conductors. 

For all practical purposes, all devices on the loop are connected directly to the panel, and the panel can't tell the difference between home runs to each device and a single daisy chain. 

Yes, the installed wiring may daisy chain to 75 devices in a straight line, but electrically, every last one of them is connected directly to the terminals of the fire alarm panel. 

For these types of systems, the wires can be thought of as having a long star-tap. 

Later Servicing the System

The real concern with the T-Taps is with the later servicing of the system. When trying to find a ground fault or bad device. A limited number of T-Taps makes it easy to divide up the system. 
Not enough T-Taps and the technician has to guess where the wires run through the building. Too many T-Taps and the technician has to pull a lot of T-Taps apart to get an idea of where to find the faulty device or wiring. 

Manufacturer's T-Tap Limit

The manufacturers that limit the number of T-Taps have an input side and an output side to each device on the SLC. Here the panel itself is creating a map of the SLC wiring system. If there are too many t-taps, or if the ins and outs of the devices are not wired according to the installation sheets, the panel's created maps become useless for later servicing. 

How Many T-Taps

When trying to determine how many T-Taps are allowed, consult the manufacturer' installation sheets, and then decide on how easy the servicing of the system should be in the coming years.

If you still aren't sure how you manage your building / establishment loop line, feel free to get in touch with one of our experts via ssaintegrate@gmail.com. Before selecting vendor / installer check and verify they are authorized or not to execute your Fire Detection & Alarm system work. Its mandatory Fire Detection & Alarm System (Edwards, ESSER, Notifier, Autronica, Cooper, BOSCH & GST etc) commissioned by certified professional.

L2 Fire Alarm

L2 Fire Alarm

IS 2189 : 2008: Indian Standard. Selection, Installation And. Maintenance Of Automatic Fire. Detection And Alarm System

IS 11360 (1985): Specification For Smoke Detectors For Use In Automatic Electrical Fire Alarm System [CED 22: Fire Fighting]

A fire alarm system is number of devices working together to detect and alert people through visual and audio appliances when smoke/fire is present. These alarms may be activated from Smoke Detectors, Heat Detectors, MCP etc.

Smoke detectors do not have a listed spacing. They have a recommended spacing of 30 feet between detectors. However, smoke detectors can be installed up to 41 feet apart in corridors up to 10 feet wide. The main fact to remember is that all points on the ceiling must be within 21 feet of the detector.

Commercial systems are categorized as follows (All include manual call points):

·         L1 – Detection provided throughout the entire premises

·         L3 – Detection provided on all escape routes and adjoining areas

·       L3/L2 – Detection provided on all escape routes and adjoining areas, as well as additional detection in specified high risk areas

·         L4 – Detection provided on all escape routes only

·      L4/L2 – Detection provided on all escape routes and additional detection in specified high risk areas

When a system is installed in a premises where there is more than one interlinked system in operation, then the suffix “X” is used.

Many fire authorities are now insisting on specific standards of fire alarm systems within buildings.  These categories are defined in the recommendations of BS5839.  One of the most common categories which is being asked for is a BS5839 category L2 Fire Alarm System.  The prefix 'L' for the category type stands for life protection.  This means that the primary purpose of a category L2 Fire Alarm is to protect life.  Whereas BS5839 system designs with a 'P' prefix are primarily designed to protect damage to property.

L2 Fire Alarm Systems are designed to offer automatic detection on all escape routes within a building, with the addition of all rooms adjoining to the escape route.  An L2 Fire Alarm design should also take into account any further areas of high risk which may not necessarily be covered with detection on the escape routes and adjoining rooms.  Examples of these areas could be boiler rooms, plant rooms and other areas with heavy plant machinery (such as in roof voids).

An Example of an L2 Fire Alarm Design

L2 Fire Alarm designs should also incorporate audible sounders throughout the building which operate when the fire alarm system is activated.  These sounders should achieve a minimum sound pressure of 65 dB (A) throughout the building and a minimum of 75 dB (A) at the bedhead where there people sleeping within the building.

An L2 Fire Alarm should also include manual call points on all exits to open air, and in buildings above a single storey all entrances to stairwells on the floors above the ground floor.  In large buildings it should also be noted that nobody should have to travel for more than 35 metres to reach a call point.  This means that further call points may be needed to be positioned within the property to achieve this.  Call points may also need to be positioned in high risk areas.  One example of this may be a paint booth where high flammable substances are present.  A call point may need to be positioned in close proximity to enable an alarm to be raised quicker should an incident occur.

Awareness of the system user is also essential, less able bodied people may or may not be capable of exiting without assistance, but high levels of people with sporting injuries or with hearing difficulties may require a system which addresses their needs.