Understanding Fire Alarm

[Alan Marriott]

Hi
I’m after some advice please I understanding a fire alarm system. I get how the conventional and addressable are wired. By my question is about when an alarm goes off. So...
In healthy state I assume there is a 24v or 12v running through the circuit? But when alarm goes off does all power drop out which I assume doesn’t or what does it do to make relays change state and also power sounders and flashing beacons?
Hope this makes sense?

Thanks

 

[Phil L]

Hi so there are 3 main types of system

2 wire - effectively in alert state the polarity is switched which in turn triggers outputs (sounders/beacons)

conventional - sounders and beacons are wired from separate circuits, when an alert is received the power switches to the sounder circuits

Addressable - a change in state of the alarm triggers a pre determined group of devices and activates there output

Thats a brief description on the 3 main types

 

[Darkwood]

Excluding domestic here...

2 primary types of system are conventional where you connect to a predetermined zone as a radial from the panel and it monitors a resistive value which is generated using common rated resistors usually in the devices and one at the end of the cable line as a monitor.

Addressable systems use a bus loop, you have a loop card and wire a large loop to which you attach your addressable devices and assign their location, type and even what you want the device to do with all in one units, addressable systems usually send a data streams constantly around the loop asking the same questions thousands of time on any given minute...

What device are you..
Are you ok...
Are you in normal state or alarm state

The panel also knows the position of each device and if say it device 8 react as OK and the next device is device 10 then it knows something is wrong as device 9 has not responded ...
This is a very crude simplified explanation here and addressable can vary too from soft addressable to hard addressable and even integration of convectional points via a special addressable connection unit, addressable panels often tell you what is wrong, where it is wrong and can isolate the problem and continue to provide cover in certain scenarios although multiple issues tend to be much harder to identify and clear.
Conventional panels only really tell you which zone is in fault and it is often a investigation to find where the problem lies.

 

[Alan Marriott]

Thanks for this info guys. So when say a call point is activated does that break the circuit to create an alert or does it change the resistance?
Also we have some interfaces for automatic doors so wanted to know also when alarm is activated how the relay is changed from say NO to NC?

Thanks again

 

[Phil L]

Ok so for a call point

Conventional is a change of resistance
Addressable is a change of analogue value (what the system looks for to indicate status)

In relation to interfaces that is effectively a relay that changes state

conventional system usually wired from the fire relay (not sounder as once silenced power is lost) fire relay applies voltage which allows interface to switch,

addressable system interface will sit on the loop and change status alongside the alarm group, when programmed to react to specific events,

 

[Alan Marriott]

Ok so for a call point

Conventional is a change of resistance
Addressable is a change of analogue value (what the system looks for to indicate status)

In relation to interfaces that is effectively a relay that changes state

conventional system usually wired from the fire relay (not sounder as once silenced power is lost) fire relay applies voltage which allows interface to switch,

addressable system interface will sit on the loop and change status alongside the alarm group, when programmed to react to specific events,

ok thank you for this. So just to clear it up when alarm goes on conventional system the relay is wired on it own from panel and voltage is applied to change its state?
And with addressable the panel on alarm sends signal etc to interface to switch state via A1 and A2 coil?
Sorry for newbie questions

 

[Phil L]

ok thank you for this. So just to clear it up when alarm goes on conventional system the relay is wired on it own from panel and voltage is applied to change its state?
And with addressable the panel on alarm sends signal etc to interface to switch state via A1 and A2 coil?
Sorry for newbie questions

Yes on a conventional system relays are usually taken direct from the Control panel, on an Addressable a signal is applied to the alarm groups on activation which changes the state of the interface

 

[Alan Marriott]

Yes on a conventional system relays are usually taken direct from the Control panel, on an Addressable a signal is applied to the alarm groups on activation which changes the state of the interface

Spot on. Thank you for your time and help on this!! Much appreciated

 

[Darkwood]

Spot on. Thank you for your time and help on this!! Much appreciated

Can we enquire, why the interest?

 

[Alan Marriott]

Sort one last question if you don’t mind please. I understand that a conventional system is wired where sounders are on one circuit and smokes and call points on another and EOL resistor placed on last point of each circuit, And an addressable is just a ring circuit around every device on system
But how is a 2 wire one wired please?

 

[telectrix]

2 wire have the detectors and sounders wired all on same radial/s. the sounders are connected reverse polarity so in a non-alarm state they don'tsound. when the panel goes into alarm, it switches the polarity over so the sounders then activate. this works because detectors are not polarity sensitive.

 

[Darkwood]

@Alan Marriott

Can you please answer the question you were asked before we continue with this thread, the numerous questions here about different systems and the way they are asked is becoming suspect, what is the interest here, is this for homework, an assignment etc or are you trying to repair, install or add to an existing fire alarm system?
Apologies for the interrogation here but we cannot advise further until we know why you are asking for such advice.

 

[Alan Marriott]

Sure no problems. I work for an electrical contractor and been qualified 2 years now. I come across different systems installed by sub contractors and am always curious to know and learn as sometimes we have to break into circuits to add devices and thought it’d be beneficial to learn and understand how these systems work for my own knowledge. Currently I’m ripping out an old conventional system as a new addressable one has been installed.
I appreciate the help and info as cleared some things up I couldn’t get my head around.

Thanks again everyone who has commented

 

[Darkwood]

Excellent, apologies again, we have to ensure you are not using the forum to effectively answer homework or assignment questions, carry on