metal ties

[David Rooney]

A good electrical contractor (there are one or two) friend of mine keeps telling me cables need to be metal clipped/tied every 300mm (ish) in order to retain their fire integrity and comply with 5839.

Our BAFE man is happy for plastic ties every 300mm and metal ties every 1m.

Any thoughts ??

[Big_Fella]

You're indeed right David, we are LPS1014, and then insist the metal tie wrap every 1 metre and plastic as you have stated

[Allen Higginson]

You aren't allowed to use plastic as the sole means of support but as intermediatery support between metal fixings.Our contractors are around the 1 metre mark for metal ties - cuts down on cost on big systems!

[Thomas Brookes]

I agree with all the above BS5839-1 says

f) Methods of cable support should be !non-combustible and" such that circuit integrity will not be
reduced below that afforded by the cable used, and should withstand a similar temperature and duration
to that of the cable, while maintaining adequate support.

!NOTE 8" In effect, this recommendation precludes the use of plastic cable clips, cable ties or trunking, where these products are the sole means of cable support.

Maybe your contractor friend only read the first part of the standard, although I do feel this is left a little to much to interpretation and should be completely clarified. Who knows if they do a update  of the standard we can get it clarified a little better.

[colin todd]

Tam, It is clear. Ask yourself if you want ties at 1m spacing holding up a length of char. If you are happy with that then its fine, but I am not sure that the cable manufacturer would be in most circumstances.

[David Rooney]

This is the issue.... to maintain the cable integrity the manufacturer (not 5839) is stating the cable must be supported as per regs... eg every 300mm using metal ties....

[Thomas Brookes]

Colin,

I think this thread proves its not clear.

Davids Bafe man said 1m metal ties with plastic in between.

Big fella's LPS1014 said the same.

I have FSA/ECA  inspections for my A3 scheme who will only accept metal ties/clips all round.

the manufactures I have spoke to want metal if not supported in another way (but not plastic clips).

So what is the correct one?

As far as I remember (please someone correct me if I am wrong) this came about because a fireman got tangled in some fire cable and unfortunately lost his life. Now if this is so would metal ties at a metre spacing cause the cable to sag sufficiently to tangle someone.

[kurnal]

Thomas
I believe the fireman losing his life however unfortunate is a red herring. In any building the fire alarm cables are less than 1% of the total electrical wiring and even if the fire alarm cables were secured on metal clips the other 99% of cables would not be so it would make no significant difference.

I believe its all about manufacturers specification - the configuration they submitted for fire testing. From trade literature and fire test reports most appear to submit their samples for testing secured with 300mm spacing between metal clips in the horizontal plane and 400mm in the vertical plane and so if relying on that fire test data we must replicate it in the field. Otherwise we are using effectively untested cable for our fire alarm system. Is that a significant hazard?  Well maybe not for some circuits on some alarm systems. I still know of many BS5839 - 1980 systems with PVC twin and earth on detector circuits. But for sounder circuits on older systems and for loops on analogue addressable systems its a different matter. In my opinion.

Meanwhile the majority of installers use plastic tie wraps as far as I can see.  And nothing at all where they think their work is unseen. 

[colin todd]

As the old genteleman says, its nothing to do with firemen getting tangled in cables. We told the world about this donkeys years ago. Sadly, the world did not listen.

[Thomas Brookes]

My opinion for what it is worth,

I believe that it is not sufficient merely to say that manufacturers  recommendations should be part of a risk assessment.
The recommendations of the individual manufacturer should be the guiding factor for such crucial
installations.
But I would welcome a move towards a consistent recommendation that can be
supported by a defined methods of verification.
Or for simplicity state in 5839-1 that any fire cables that have to be supported by clips/ ties etc must use metal fixings at maximum of 300mm.
Just on this forum we have several different "correct" methods of cable fixingi, surely this shows that it is not clear.
I was recently at a big warehouse in Carlisle, and saw that the brand new fire alarm system is totally held up with plasic ties (not a single metal fixing anywhere) and this was a fair sized fire company not a sparky contractor.

[Wiz]

I think the BS recommendation on this point is clear and perfectly written. I don't think it needs to be elaborated.

A leading manufacturer of fire resistant cables explained to me that a certain amount of movement of a cable during a fire may affect it's continued fire resistance. Hence the need for the fire resistance of the support of a cable being at least equal to the fire resistance of the cable.

The affect of movement was explained to me as follows: If a fire resistant cable is subjected to enough heat, a chemical reaction occurs that causes the otherwise flexible fire resistant cable to become brittle whilst still maintaining it's fire resistant properties. However movement of the cable in it's brittle condition can cause the the brittle layer to crack open and allow flames access to the cable cores and destroy them quickly.

The need for correctly supporting a fire resistant cable is therefore of paramount importance.

However, It is up to each cable manufacturer to confirm at what intervals their particular cable needs to be supported to maintain fire resistance.

If the BS was to include a specific recommendation, say for example, every 600mm, and I invented a cable that only needed to be supported every 1000mm, I would be prevented from using this greater fixing distance intervals as a unique selling point for my cable because of BS!

[GregC]

However, It is up to each cable manufacturer to confirm at what intervals their particular cable needs to be supported to maintain fire resistance.

With my patented marking scheme of H stamped every 300mm and V every 400mm it would make life a lot easier.

btw, who would issue a commissioning certificate with variations if they found the cables with plastic clips or ties or in MMT2/conduit with no metal support anywhere, and who would not issue a commissioning certificate until it was rectified?

[Big_Fella]

The commissioning engineer is responsible for ensuring the system is fully testing and operational, it's not necessarily the commissioning engineers responsibility for the installation of the system.

The engineer 'should' check where pratical the installation of the system complies, but realistically this may not be possible (cables at high level/concealed etc).

This would relate to the installing party when it comes to issuing the installation certificate.  Will they provide such documentation to confirm that the system is installed correctly?  Many a times the installation certificate is never produced !!

[Wiz]

However, It is up to each cable manufacturer to confirm at what intervals their particular cable needs to be supported to maintain fire resistance.

With my patented marking scheme of H stamped every 300mm and V every 400mm it would make life a lot easier.

Greg C, your patented marking scheme of H every 300mm and V every 400mm will be no good for my imaginary newly invented cable that enables wider spacings 

However, I will mark the cable with H's and V's at the appropriate spacings to suit my cable, because your idea is a good idea.

Obviously where the H's and V's coincide it will say H & V and everyone will just think it is a cable for the air-conditioning unit!

[GregC]

Obviously where the H's and V's coincide it will say H & V and everyone will just think it is a cable for the air-conditioning unit!

Dammit, foiled again......