Cable tray fittings : Names and functions

 fire alarm panels

Most fire alarm panels are plugged into  an AC power and have a rechargeable batteries inside it .

220V or 110V AC voltage is converted to 24V DC voltage to feed the fire alarm system and at the same time two 12v batteries connected in series  are charged  to produce 24V dc which is used to feed the fire detectors and the entire fire alarm system in case of mains failure

Fire alarm panel 

 Conventional fire alarm systems

In this system the fire detectors are connected in parallel ,the cable exits from the positive end of the fire alarm control panel (FACP) to the positive end of the first detector and from the negative end of FACP to the negative end of the first detector and then from the positive end of the first detector to the positive end of the second detector and from the negative end of the first detector to the negative end of the second detector and so on,so  all of detectors are connected in parallel and the two ends of the last detector are open  

What will happen if the last two ends are left open ?

The panel will detect a false permanent open circuit fault and if a true open circuit fault occur in the cable connecting between the detectors, this true fault will not be distinguished from the permanent open fault at the end of the zone

What happen if the last two ends are short  circuited ?

 The FACP panel will detect a short circuit fault ....  To solve this problem , high resistance with a value may range from 5 to 10k ohm is connected with a large value ranging from 5 to 10 Koh between last two ends of the zone and this resistance is called end-of-line resistor (ELR)

 Why this high value resistor is added ?

 because according to the ohm's law (I=V/R) the higher the resistance the less the current drawn and we are here in a light current circuit and also the detectors have a large resistance (from 1 to 10K ohm) 

And the group of detectors connected together in parallel with the same cable from the FACP panel  is called " Zone"

Each zone is indicated at the FACP panel either with an indicator lamp or text display or the both. 

Conventional fire alarm system 

Wiring detectors in conventional fire alarm system

The following figure shows the way of  wiring detectors in the fire zone as
 the red line represent the wire which connects the  positive ends (+) of all detectors and the black line represents the wire connects the negative ends ( - ) of all detectors and the dotted blue line represents the earthing wire which connects all earthing terminals in all detectors together .

the wiring of the entire system is shown in fig :

  from the previous  figure we find that :

• Break glass (also called manual pull stations) and detectors can be installed in the same Zone .

• Audible alarm devices (like Bells ,serines ,horns) and visible alarm devices (like strobes or flashers) are installed in an independent zone .

Disadvantages of Conventional fire alarm system 

The conventional system can be considered non intelligent system for example if we have a conventional system installed in a building and suppose that a 30 detectors are installed in only one fire zone in different rooms  inside  the  building .
If a fire occured in one of these rooms and the room's detector was activated , in this case the FACP panel will give alarm and indicate that there is a fire in the whole fire zone not the room the fire occurred in so the conventional system is used only inside small  buildings

Maximum number of detectors per zone

In a conventional system, a maximum of 30 to 33  detectors can be installed in a single zone and this number differes according to the manufacturer of system .

 Applications  of conventional fire alarm system

Conventional system is used in buildings with limited  area and few floors where a limited number of detectors can be used

Addressable fire alarm systems

In addressable systems , the detectors are wired in a closed loop as the fire alarm cable (consists of two wires (+,-)) exits from the FACP panel and connects all detectors in the same way as in conventional system but the cable returns again to the FACP panel .

Connecting detectors in a closed loop increases the reliability of the system because if a break occured in the wires of fire cable , all the detectors or devices (after the broken wires) will still be connected to the FACP panel through the other direction.

Addressable fire alarm system

Reliablity of conventional and addressable system

Each detector or device (break glass , sounders and flashers) in the system is programmed to take a unique address so that in case of fire ,the address of  activated detector will appear in the FACP screen and the location of fire will be detected accurately .

The detectors and alarm devices are programmed via a special programming device or via the device itself .

Notes :

• Break glasses (manual pull stations) and detectors are connected in the same loop .

• Audible and visible alarm devices (serines,bells,horns,strobes..etc) are installed in an independent zone and  an end of line resistor is installed at the end of zone .

• In some brands of addressable fire alarm systems, the Audible and visual alarm devices and detectors are wired  in the same Loop .

Methods of programming Addressable fire alarm detectors

The fire alarm detectors in addressable systems are programmed in several ways depending on the detector's manufacturer these methods are : 

1) Using "address card"

A card contains several buttons is used and each button has a number beside it as follows : 1 , 2 , 4 , 8 , 16 , 32 , 64 and this card is fitted in the detector base .

To obtain a specific address with a specific number, one or many buttons (each button has a number written beside it) are removed so that the sum of the numbers beside removed buttons gives the required address as shown in the next figure :

Suppose we need to get an address (10) so the two buttons that have the numbers 2 and 8 should be removed as their sum (2+8) equals 10 .

2) Using Electronic programming device 

In this method , the detector is connected to a special electronic programming device which has a small screen and keyboard and the programmer can write the address using the keyboard and read the address through the small screen .

detector programming device

3) Using DIP switches

DIP stands for Dual In-line Package
In this method DIP switches are fitted in the detector base as in the following fig :

Each switch has two positions (on , off) and there are 8 switches (1 through 8) all of them work in binary
As we said before the switch has two positions (on,off) , the position off means zero but the position on of the switch gives the values stated in the following table :

Example : if we want to give an addressable detector an address of (99) we will take the following steps:

• The switch "1" is turned on and get 1
• The switch "2" is turned on and get 2
• The switch "6" is turned on and get 32
• The switch "7" is turned on and get 64
• All other switches are turned off
• The sum is 1+2+32+64=99 and this is the resulting address 
• The following picure show the previous addressing process :

4)  Decimal address switches

The detector is given an address by using two switches, the first switch represents ones and the other switch represents tens of the number or address required to be given to the detector .
The switch of ones has 10 positions (0 through 9) .
The switch of tens has either 10 positions (0 through 9) or 16 positions (0 through 15) .
Each switch of them has an indicator which can be turned to get the desired number .

For example, an addressable detector is needed to be given the address 37 , how ??the ones switch  is set to number 7, and the tens switch is set to Number 3, so we get the address 37.
The detector then converts this digital number 37 to the binary number 100101 and sent it as a signal over the wires to the FACP panel .

5) Automatic addressing 

In this method , the FACP panel gives addresses to all of the devices connected on the loops automatically depending on the physical position of each device on the loop.

Advantages of addressable fire alarm systems 

• The addressable fire alarm system is more reliable the the conventional system because the addressable devices are connected in a loop and at both ends to the panel and if there is any break in the wires or loop or all the remaining devices will still connected .

• False fire alarms are reduced to minimum as even dust or contamination around the detector which can cause false alarms can be monitored by the detector itself. 

• The cost if wiring up the addressable system is cheaper than the conventional system because in some addressable brands all the detectors, break glass ,serines, bells,horns and strobes can be connected in the same loop unlike the conventional system which uses an independent zone for audible and visible alarm devices .

• The addressable fire alarm panel can check and monitor all of the devices connected in the system so if any problem or issue occured to any detector this fault is discovered by the FACP panel which makes maintenance of the system much easier than than the conventional system.

Applications of addressable fire alarm systems 

Thr addressable fire alarm system is usually used in larger buildings ,hospitals,shopping malls and university campuses where there are a number of large-area floors and it is necessary to detect the precise location of fire very quickly  to start evacuate large number of people in these buildings .

Can the addressable fire alarm panel be used instead of a conventional panel ?

Yes, of course but the opposite is not true

But this will lead to unnecessary higher cost .

Isolator module in addressable fire alarm systems 

The isolator module is a module used in the addressable fire alarm system and is installed after each group of detectors in the single Loop (approximately every 20 : 25 detectors depending on the system brand) 

Isolator module 

Function of isolator module

 if a short circuit occured in any part of any loop of the fire alarm system ( an example a short circuit between the two wires of the fire alarm cable) the isolator module will  isolate this part from the loop and keep the remaining detectors fed  from the two directions of the Loop (like two zones)  until the short circuit fault is cleared. 

The isolator module is usually installed after each 10 detectors (or more depending on the manufacturer) and isolates these 10 detectors in case if short circuit occured.

Wiring of isolator module

The following figure shows the wiring of the isolator module

Wiring of isolator module

An example of using isolator module 

The isolator module may be used inside a  single loop which connects all the detectors of all floors of a building and at each floor in the building , two isolator modules are installed at the beginning and end of the detectors of each floor 
In any floor in the building , if a short circuit occured in the loop wires then the two isolator modules installed at the beginning and end of this floor will isolate all the detectors of this floor but the remaining detectors of other floors will still connected and operate through the two directions of loop .

Detector with isolator base

Sometimes , detectors with isolator module base can be used instead of a separate isolator module and in this case ,only two detectors will be isolated from the loop instead of isolating 10 or more detectors if the separate isolator modules are used but the whole system cost will be more expensive. 

detector with isolator base

Remote LED indicators in  fire alarm systems

Remote led indicator 

The remote led indicator is a device that contains a small LED lamp and is connected through two wires to the base of the detector to give an indication to the status of the detector which it is connected to as it will light whenever the detector gives alarm and activated. 

Remote led indicator is used when the detector is located out of sight or it is difficult to see its status like in a ceiling void , behind a locked door , roof spaces, in lift shafts and escalator machine rooms then the indicator will then show the location of alarm .

It is compatible with both addressable or conventional systems and when it is used with an addressable detector it takes the same address as the detector .

Some versions of led indicators can be connected to more than one indicator located in the same room to show the status of any of these indicators whenever it gives alarm .

Wiring of remote led indicator

  fire alarm repeater panel

Repeater panel

The repeater panel is used in addressable fire alarm systems in these situations :

• When there is a need to install an addressable fire alarm system in a building which is far away from the main FACP panel existed in the main building so we use a repeater panel in this building as an extension to the main FACP panel and is connected or linked to it .

• If there is a main FACP panel that all its loops  reached to the maximum number of detectors or alarm devices that can be connected to them and there is a need to add new fire alarm devices to the  system so we can use a repeater panel and add the new devices to it and connect this repeater panel to the main FACP panel .

• When the main FACP reaches the maximum number of loops that can be connected to it so a repeater panel is used and any required new loops are connected to it .

The repeater is suitable for up to 8 zones and displays all the same functions as the main FACP panel , but with the addition of an indicator test facility .

Types of  fire alarm repeater panels 

There are two types of repeater panels :
Active repeater panel :  it provides full information  or indication of events at the main panel and also provides controls of fire system from the repeater panel 
Passive repeater panel: it provides partial indication of events and no control .

Wiring of  fire alarm repeater panel

The connection between main FACP panel and Repeater paned is achieved by using two cables ,the first cable is a power cable and the other cable is a data or communication cable (RS485 cable)