fire alarms

[james king]

hi all. i was just wondering if some could possibly tell me the dirrfrence between bi-wire, addressable and conventional fire systems. i am confused about the bi wire system as its just loop in and out eg. 2x cables in one smoke head! but then what is the diff between that and bi wire? any diagrams would be good cheers

 

[Guest123]

Here is a VERY basic guide to fire alarm terms & definitions.....

Basic Guide to Fire Alarm Installation


Fire alarms are not something to be taken lightly as at the end of the day they can prove the difference between life and death. There are some good training courses here.....

FIA Training Courses

 

[james king]

thanks lenny but stil does not explain the differnce between the 3. im just wondering as i have only staterd my 1st year apprentiship

 

[accordfire]

hi all. i was just wondering if some could possibly tell me the dirrfrence between bi-wire, addressable and conventional fire systems. i am confused about the bi wire system as its just loop in and out eg. 2x cables in one smoke head! but then what is the diff between that and bi wire? any diagrams would be good cheers

If only that's all there was to it.

Twin wire (NOT Bi-wire - that refers to wiring of audio speakers in a specific pattern) systems are exactly that - they use two wires to accomplish connection of field devices, warning devices and ancillaries to the control equipment.

Conventional systems do much the same thing - though field devices are run on different circuits than warning devices.

Addressable systems......can be analogue or conventional hybrid. As the name applies, each device is "addressed" so as to be individually identifiable by the control equipment.

To be honest, if you are confused about basics such as the topology of a system, diagrams aren't going to help you any at all.

Best thing to do would be to learn about why a fire alarm system might be needed in the first place, what it does, what its application might be in a given situation, and most of all, about proper design of fire alarm systems in buildings - and in that way, you will not only answer the question you have asked, but you will also come to understand why "how the system is wired" is one of the last things you need to bother about - unless you're installing to someone else's design, in which case, you need to learn about proper installation procedures - and compliance with BS5839.

Sorry, my friend, but fire safety is NOT about throwing a few smokes in and job done.

 

[telectrix]

conventional alarm

 

[james king]

ok i was only asking!! im not installing anything just sat at home bored and thought about it, that was all! i was just wondering why it is called a 2wire system if a convention system id 2 wire as well. eg loop in- out

 

[accordfire]

ok i was only asking!! im not installing anything just sat at home bored and thought about it, that was all! i was just wondering why it is called a 2wire system if a convention system id 2 wire as well. eg loop in- out

The fundamental difference is that a twin wire system will contain, on each pair of wires, both field devices (e.g. smoke detectors, call points) and warning devices (e.g. sounders, strobes). A conventional system will only contain one or the other on each pair of wires.

There are other differences too, but that is the essential difference.

 

[james king]

so there fore has a quicker install time??? less running of cables? so am i correct in saying that 2zone panel will contain of 2zones being smoke,call point and heat, then a seprate circuit for sounders?

 

[telectrix]

conventional system is 2 wire, daisy chain, no spurs, . radial cct. for each detection zone . ditto for sounder ccts. EOL device at final point of each cct. addressable are more complex. Bill is our acknowledged expert on Fire.

 

[accordfire]

so there fore has a quicker install time??? less running of cables? so am i correct in saying that 2zone panel will contain of 2zones being smoke,call point and heat, then a seprate circuit for sounders?

In theory, yes, a quicker install time and less cable.

Separate sounder circuits are conventional. On twin wire systems they go on the same pair of wires as the field devices.

So, what you're describing above is a conventional system.

 

[james king]

i get it now. are the 2wire systems used more often, in say flats?

 

[accordfire]

i get it now. are the 2wire systems used more often, in say flats?

No, not necessarily.

Flats are subject to specific fire rules as they are HMO properties.

This is why it is imperative to learn about fire alarm design first. There is no hard and fast "use this type of system for this type of property" rule.

The choice of wiring system is determined by the design requirements of the installation, by the British Standard, by Risk Assessment criteria, and by other authority input, usually in that order. It isn't something you can "just do".

Twin wire systems specifically are most often used because of constraints placed where an earlier system was already installed. They are also used, as you said, to save labour time, though they have inherent weaknesses too, which must be addressed at the system design stage.

If by "two wire" system - you actually meant conventional, this time - well, they are used almost everywhere - it is the de facto standard for installation of a fire alarm system, even today.

Analogue addressable systems are used primarily for larger systems.

 

[james king]

i see. we went to see a job the other day (me and my boss) and the flats were flooded!!! the insurance want all smoke, heat, sounders and call points changed. i was trying to see inside the smoke when he was taking it off but could really see much. how is a 2wire system wired diffrently from a convenional? i rememer he said some thing about the -wire goes across the resistor and +wire connects in to one terminal ?? u have been very helpfull and i am greatfull for you respnonse

only trying to learn

 

[accordfire]

i see. we went to see a job the other day (me and my boss) and the flats were flooded!!! the insurance want all smoke, heat, sounders and call points changed. i was trying to see inside the smoke when he was taking it off but could really see much. how is a 2wire system wired diffrently from a convenional? i rememer he said some thing about the -wire goes across the resistor and +wire connects in to one terminal ?? u have been very helpfull and i am greatfull for you respnonse

only trying to learn

Trying to learn is ALWAYS a good thing. It's what you do with what you learn.......the point I was trying to make, and often try to make, when people come into the forum asking away for help with things like you have, is that there is a danger they may use that knowledge, thinking they're doing things right, when in fact, they're not.

The thing about fire alarms, is if you get it wrong it can cost a life very easily. That's why design knowledge is essential, and why it's good to be very specific about why you're asking the question - it's not personal in the way you took it earlier - it's meant to make sure nobody gets into a dangerous situation.

Anyway - essentially, a twin wire system is wired in much the same way as a conventional system - i.e. devices are wired in parallel across a positive and negative line. Twin wire systems such as Rafiki generally have built in end of line selectors, so no additional end of line monitoring is required - you simply set the last device on the line to be "end of line".

With conventional wiring, which is what I suspect you saw the other day with your boss, the principle is similar. You have a positive, and a negative. However, on the base you will have a diode (not a resistor) - through which the positive (not the negative) must go - so you'll have something like "L1 IN" and "L1 OUT" plus an L2 on the base.

Simply the positive feed from the last device (or panel) goes to L1 In and the positive feed to the next device connects to L1 OUT. L2 is for your common negatives (i.e. in and out).

Resistors are used for end of line monitoring, so you would only have seen a resistor in the base, had it been an end of line, in which case, there should only be one cable present.

The purpose of the diode across L1 In and L1 OUT is to detect head removal. Twin wire systems accomplish head removal detection by use of electronics inside the device itself.

 

[james king]

i thought i seen the black wires connected acros the diode and the reds all connected to gether! i had a look at the diargam for a smoke in his van on the way home and it said the -should go across the doide not the possitive?? confused are there any diargams i can see! just wan to get my head around it