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Topic Title: PVC and LSF Cable
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Created On: 06 January 2008 09:53 AM
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 06 January 2008 09:53 AM
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markLEDS

Posts: 121
Joined: 09 August 2007

Happy new year all,

Can anyone tell me if there is any documented guidance on the use of PVC or LSF cables. As in when you should use PVC and when you should use LSF?

I understand the reasons for using the LSF or LSZH cable insulation but need to understand if there is any guidance on it's use document by an 'official' source.

Many Thanks,

Mark
 06 January 2008 02:44 PM
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lyledunn

Posts: 615
Joined: 13 August 2003

You will find prescription in documentation relating to specifications for electrical installations in certain public buildings,estate services directorate for hospitals for instance. However, I am sure that you are aware of the general move from prescription to a more risk-based approach. Risk assessment is an obligation in statutory documents such as the relatively recent Fire Safety Order 2005. Thus the effects of fire in a building must be carefully considered by the responsible person and the intrinsic value of LSF type cables would be a consideration any prudent assessment would need to evaluate.

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Regards,

Lyle Dunn
 07 January 2008 08:23 PM
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markLEDS

Posts: 121
Joined: 09 August 2007

Thanks Lyle,

It was actual documentation i was looking for but your comments raise a valid point that i had not considered.

But, if this is the method of choosing cable types when will PVC ever be used? When will the risk of fumes from PVC ever be considered a managable risk that could be justified in a risk assessment when a lower risk option is available?

Thanks,

Mark
 08 January 2008 12:24 AM
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formston

Posts: 1
Joined: 18 January 2003

Hi Mark,

Whilst I'm involved in the aircraft industry, perhaps my recent investigations may help.

I'm currently performing a risk assessment involved with PVC wiring removal from older aircraft. I've realised that there are sound reasons why the US Airforce discontinued installation of PVC in 1977. A very good report is provided at Link removed/pdf/TN04-32.pdf showing the effects of burning wiring.

PVC is often advertised as "fire resistant," meaning that a fairly high temperature is required to start it burning. However, PVC starts to smoulder and release toxic fumes such as hydrochloric acid at a lower temperature, long before it ignites. If PVC is gradually warmed, more than half of its weight is given off as fumes before it gets hot enough to burst into flames. The hydrochloric acid released by burning PVC is potentially lethal to people caught in a burning building; other products of PVC combustion, such as dioxin, exert their health effects more slowly and are spread across a larger population. When it burns in an aircraft it produces copious amounts of black smoke also rendering pilot's vision extremely difficult. PVC has a low temperature rating, is more susceptible to chafing and ageing and even when the heat source is removed, exhibits the longest burn length and tends to drip.

It's nasty stuff and I would always recommend a proper safety evaluation of an installation.

Cheers
Gef Formston CEng MIET
Senior System Safety Engineer
 10 January 2008 12:13 PM
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markLEDS

Posts: 121
Joined: 09 August 2007

Gef,

Thanks for your comments, most inciteful and intersting.

It would appear though that there is no specific published guidance or standards for its use, which I find suprising.

Thanks for the comments Gents.

Mark
 10 January 2008 12:33 PM
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Jaymack

Posts: 4625
Joined: 07 April 2004

I would think the criteria in determining the use of LSF cable, would be dependent upon the likelihood of toxic fumes being released into confined spaces; or general areas, where persons, (or perhaps livestock in cases) may be present or congregate - tunnels, public theatres, concert halls, sports arenas and educational establishments etc. Specific authorities/consultants would probably have their own specifications.

Jaymack
 10 January 2008 12:40 PM
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markLEDS

Posts: 121
Joined: 09 August 2007

Jaymack,

As I have said above, when can realeasing toxic fumes ever be acceptable for a risk assessment to use PVC rather than LSF other than a building that wont ever be occupied? thanks for your comments though, they back up my thinking.

As a "consultant" (hate that term) I write specs all the time and nearly always use LSF cables for the reasons above.

The problem i have is occassionally contractors will offer the client savings to use PVC. Some clients accept what i tell them but others ask me to tell them where it states you need to use LSF cable, otherwise i'm accused of wastig their money.

Thanks

Mark
 01 May 2009 05:06 PM
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deant

Posts: 2
Joined: 29 October 2008

Hi Mark

I have struggled with this same question myself. I have asked on other forums for, which or what regs backs up your argument for using LSF cable. I had no joy and came to the conclusion like this thread its up to the risk assessment. Have you ever had a independent risk assessment, they are so much on the what if's, it prices everybody out of the market. As you have said in a public building LSF would beat PVC every time.

I have designed in train stations and hospitals, and prior to even starting it was stated LSF throughout the job.

Regards

Edited: 01 May 2009 at 05:07 PM by deant
 01 May 2009 05:19 PM
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Avatar for OMS.
OMS

Posts: 19591
Joined: 23 March 2004

One problem I find with "LSF" specs is that they fail then to prohibit significant quantities of plastic (PVC) containment - which tends to defeat the object somewhat. I find it quite ironic when looking at LSF cabling in PVC dado trunking when you consider the relative volumes of material involved

Regards


OMS

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 01 May 2009 05:47 PM
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deant

Posts: 2
Joined: 29 October 2008

Hi

I know what you mean, its go to be all or nothing.. National rail required us to use LSF cable ties as well, we did install the cable on galvanised tray though not in PVC trunking. We don't seem to have the range of LSF cables in this country as yet, try ordering a super tuff flex in LSZH cable..

can you buy white LSF trunking??

Regards
 01 May 2009 06:08 PM
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Avatar for OMS.
OMS

Posts: 19591
Joined: 23 March 2004

Well to be fair, most xlpe cables are LSF anyway. I can't say I've seen "LSF" trunking per se - although I've never seen galv steel trunking give off any fumes either

OMS

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Failure is always an option
 02 May 2009 06:56 AM
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kj scott

Posts: 2144
Joined: 02 April 2006

422.2.1 refers to cables in escape routes being low smoke production.
The specification of LSF cables is often just over precaution; by the time the wiring is producing fumes you should be out of the building; or you are probably already dead. Every thing else in the building is aready creating enough hazards; computers; furniture; carrier bags etc.
Surface wiring in significant quantities should be LSF however.

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