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james.wilson

Do Fire Alarm Circuits Need To Be Segregated From All Other Circuits

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There has been a thread here about this.

I thought it better to create a seperate thread to debate this as there is obviously a difference of opinion.

 

It is my position that fire cables DO need to be seperate or segregated from all other circuits.

 

From BS5839

The circuits of fire alarm systems need to be segregated from the cables of other circuits to minimize any potential for other circuits to cause malfunction of the fire alarm system arising from:
— breakdown of cable insulation of other circuits and/or fire alarm circuits;
— a fire caused by a fault on another circuit;
— electromagnetic interference to any fire alarm circuit as a result of the proximity of another circuit;
— damage resulting from the need for other circuits to be installed in, or removed from, ducts or trunking containing a fire alarm circuit.
In order to facilitate identification of fire alarm circuits, cables should preferably be red in colour, unless another form of colour coding is appropriate. By this means, the possible need for appropriate segregation can be identified, and there will be less likelihood of inadvertent manual interference with the circuits of fire alarm systems (e.g. during work on other electrical circuits).

The belief that 7671 overides in this area appears to be incorrect. As it IMO only applies to the incoming power supply cable not the elv cables

As stated in 25.2h) wherever possible the circuit supplying a fire alarm system need not be protected by an RCD. The 17th Edition of the IEE Wiring Regulations (BS 7671:2008) introduces a number of new requirements for the installation of RCDs. Regulations 522.6.6; 522.6.7; and 522.6.8 concern cables concealed in walls or partitions.
Reference should be made to these regulations when considering which cable type will be used for the mains supply for the fire alarm system, as not all cable types that meet the requirements to be classified as “standard fire resisting cables” or “enhanced fire resisting cables” in BS 5839-1 will provide an adequate level of mechanical protection to satisfy the requirements of 522.6 in BS 7671.
It should be noted that the requirements for mechanical protection in 522.6 are specifically aimed at the issue of penetration of concealed cables by nails, screws and the like.
Consideration could also be given to running cables supplying fire alarm systems on the surface in some cases.$

Another Quote

k) To avoid the risk of mechanical damage to fire alarm cables, they should not be installed within the same conduit as the cables of other services. Where fire alarm cables share common trunking, a compartment of the trunking, separated from other compartments by a strong, rigid and continuous partition, should be reserved solely for fire alarm cables.
l) To avoid electromagnetic interference with fire alarm signals, any recommendations by the manufacturer of the fire alarm equipment in respect of separation of fire alarm cables from the cables of other services should be followed.

and

Segregation needs to be in accordance with the recommendations of 26.2l) and Clause 28 and by using cable suitable for the highest relevant voltage in the fire alarm system and in the other circuits relevant to the segregation.

Seems pretty clear that if it is not segregated its a variation and must be noted as such


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The "shoulds and coulds" are a joke in this document (5839) and imo variations need looking at as well because theres nothing stoping you wiring it in coax and using a variation!

We have always asumed in 5839 that shoulds are "musts" and install to that idea, the only variation we have used is mcp hight to match other switches ect on new build

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as james says,tho ive seen it in the same trunk as power be it short or long runs,i treat it as alarm cable only for short runs adj power if no other option,tho i do prefer it in its own trunk/conduit or tray when surface ran,not a fan of clipping when its on show

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Put it in plastic trunking inside the metal then!

Technically still seperate!lol

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As I stated in my other thread I believe 5839 is wrong on this issue and it hasn't been thought through by the people writing the standard. In James first post i'll just highlight what is wrong and why. I am of the personal belief that fire alarm cables can be ran along side mains with no issues what so ever. I have ran this idea past many tradesmen, technicians and manufacturers and not one has yet to disagree other than "regulations say so" 5839 is a good practice guide for the installation of an electrical circuit. Nothing more, nothing less. It doesn't have different characteristics and doesn't behave any differently from any other type of circuit and should be treated exactly the same in terms of use, protection and segregation. What is stipulated in 5839 is GREY at the best of times and to me, is just plain old best practice. We all know best practice is what we strive towards and work with but it's not always achievable. The situations that i'm referring to when I say that 5839 is when there is no segregation available, the situation is too awkward to provide it or you have the chance to save yourself some money and hours. 

 

 

The circuits of fire alarm systems need to be segregated from the cables of other circuits to minimize any potential for other circuits to cause malfunction of the fire alarm system arising from:

— breakdown of cable insulation of other circuits and/or fire alarm circuits;
— a fire caused by a fault on another circuit; Irrelevant. The cable is fire rated.
— electromagnetic interference to any fire alarm circuit as a result of the proximity of another circuit; By following 7671 this is a non issue.
— damage resulting from the need for other circuits to be installed in, or removed from, ducts or trunking containing a fire alarm circuit. By By following 7671 and good practice as an electrical installer this is minimized to the extent of is again being a non issue. 
In order to facilitate identification of fire alarm circuits, cables should preferably be red in colour, unless another form of colour coding is appropriate. By this means, the possible need for appropriate segregation can be identified, and there will be less likelihood of inadvertent manual interference with the circuits of fire alarm systems (e.g. during work on other electrical circuits).

 

 

 

 

[k) To avoid the risk of mechanical damage to fire alarm cables, they should(Should! because it's best practice, not for any technical reason) not be installed within the same conduit as the cables of other services. Where fire alarm cables share common trunking, a compartment of the trunking, separated from other compartments by a strong, rigid and continuous partition, should be reserved solely for fire alarm cables.

l) To avoid electromagnetic interference with fire alarm signals, any recommendations by the manufacturer of the fire alarm equipment in respect of separation of fire alarm cables from the cables of other services should be followed.By following 7671 when installing cables this doesn't matter because your screened cable has minmised the effects of interference.

 

 

I understand that if you work in this way it's not to best practice and requires a variation. Which in itself is silly because you can do anything you want to a fire alarm as long as you pass on the responsibility so hey, who cares? But 5839 is too grey to be considered a concrete technical document. If they don't want people to interpret and implement then they need to remove the factors that allow it in the first place. In my opinion a solid technical idea should be used over best practice. The inspectorate would rather you spend time and money and have everything done to the letter of the law because at the end of the day it's not their time, nor their profit that they are pissing down the drain. They get to come at the end of the job, when all the hard work and swearing has been done and then pick things off. 

Edited by Scotmod

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Quote

— electromagnetic interference to any fire alarm circuit as a result of the proximity of another circuit; By following 7671 this is a non issue.

Scotmod. What part of 7671 are you quoting on this? 

 

Previously I have run mains cabling and fire alarm/ELV/data in the same tray but with a divider to separate them. This was agreed by everyone and signed off by the Clients consultant. 

 

in the NON-mains side, I was under the impression that the voltages in fire alarm, data and security (Power Over Ethernet - in our case) were so low that they would not cause any interference with each other. 

 

This has always been a grey area in 5839. I think a lot of older generations do not agree with running fire alarm and data together!  

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As per the OP, BS5839 states that as fire alarms are a safety system, cables must be segregated from all others and therefore have there own containment or segregation within tray or trunk.

 

In reality interference will be minimal if kept with ELV circuits but that's what in stated in the standard.

 

Not seen Scotmod around for a while, so bumping this old thread may not answer your question. However, the way I read it is that by conforming to BS7671 you cannot get interference, I don't agree.

 

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Posted (edited)

Certainly the Fike manual tells you to keep fire cables at least 20cm (IIRC) from any other electrical cable - and if you wanted to rely on BS7671, that also compels you to follow manufacturers instructions, so...

 

As above, @Scotmod hasn't signed in for about 3 years, so better to start a new thread. And, welcome :)

Edited by datadiffusion

So, I've decided to take my work back underground.... to stop it falling into the wrong hands

 

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1 hour ago, datadiffusion said:

Certainly the Fike manual tells you to keep fire cables at least 20cm (IIRC) from any other electrical cable - and if you wanted to rely on BS7671, that also compels you to follow manufacturers instructions, so...

 

As above, @Scotmod hasn't signed in for about 3 years, so better to start a new thread. And, welcome :)

You try keeping it away by 20cm in allot places very difficult 

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It’s seems daft to me when you think that the cables in the panel like the zone, loops, sounder circuits etc  are close to the mains cable and connections

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Inductance is measured over a conductors parallel length, this is why you may cross cables perpendicularly but they must have separation/segregation when parallel.

  • Upvote 1

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21 hours ago, al-yeti said:

You try keeping it away by 20cm in allot places very difficult 

Agreed, virtually impossible at times.


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11 hours ago, sixwheeledbeast said:

Inductance is measured over a conductors parallel length, this is why you may cross cables perpendicularly but they must have separation/segregation when parallel.

:yes:


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