Compatability of fire alarm wiring

[FireDave]

Dear All

Can anyone advise me please on the compatability of enhanced wiring for a fire alarm system in relation to standard wiring.

I won't bore you with the history, but I have a situation in a hospital where a fire alarm system was installed pre 1996 and has been updated recently with the provision of new devices but the original wiring has been retained and the original system was install using standard wiring.

We are now in a position to improve the standard of coverage to L1.  The current BS 5839 and HTM 05-03 Part B both state that hospitals should have enhanced wiring.  However the option of replacing all the wiring is a non starter due to the cost implications.  My query is are the two types of wiring compatible and would the sensible approach be to accept the additional circuits in standard wiring so that at least we have the full coverage and use the certification to identify the variation from the BS.

Thanks for any advice you can give

[Wiz]

'Enhanced' grade fire-resistant wiring is recommended by BS5839 where the fire alarm system is installed in unsprinklered buildings of greater than 30m in height or where the occupant evacuation strategy involves 4 or more stages or on critical parts of a networked system. It can also be recommended in any system on the basis of a fire risk assessment.

Hospitals are given as a potential example and not as a definitive example of where 'enhanced' grade is required due to evacuation strategies.

The category of system has no bearing on the potential requirement for enhanced grade cable.

A variation can be notified for any deviation from BS recommendations.

Whether any such variation is acceptable to the 'relevant persons' is another matter entirely.

[FireDave]

Thanks Wiz, your comments are greatly appreciated

[Galeon]

Enhanced cabling , only in relation to alarm / sounder circuits , thats how I read it as it was all to do with the ability of soft skinned cables in relation to the burn test and the additional water spray test . 

[David Rooney]

Enhanced cabling , only in relation to alarm / sounder circuits , thats how I read it as it was all to do with the ability of soft skinned cables in relation to the burn test and the additional water spray test . 

Ayyy ?

Sorry lost me there...!

[Wiz]

Galeon, the grade of cable is required throughout the critical signal path. This is from the point of detction, for example, mcp, right through to the alarm warning device, for example, sounder.

Standard grade fire resistant cable will withstand the test for 30 mins and the enhanced grade for 60 mins.

Any type of cable (not just soft skinned types) would need to meet the relevant test.

[Galeon]

When the BS was written the only cable that met this was mineral , still only certain soft skin cable now only meet equal and approved to mineral , not withstanding that mechanical protection must be provided on soft skinned where damage ie drop to call points might occur.

[Wiz]

Galeon, I think you are spot on with your recollection that only MICC cables achieved the required fire resistance recommended at the time of the introduction of the 2002 version of BS5839 part 1.

Whilst mineral insulated copper clad cables were formerly often the most recognised cable for use as a fire resistant cable in fire alarm systems (and often only required on the alarm warning device circuits and not the whole of the csp as today) other cables such as steel wire armoured and even pvc singles in metal conduit were deemed to provide sufficient fire resistance in some circumstances.

The actual current fire resistance ('standard' and 'enhanced' grade) tests were obviously developed to provide a benchmark that any cable could aspire to reach to be considered as having an acceptable fire resistance for use in fire alarm systems.

The BS recommendation for mechanical protection to fire alarm cables in some circumstances has nothing to do with fire resistance and everything to do with protection from physical damage likely to be caused to it due to the environment and/or location in which it is installed. At the time of writing, I haven't got my copy BS in front of me, and I don't recollect this further mechanical protection recommendation being only applicable to 'soft skinned' cables. Maybe someone can check if they have a copy of BS5839 Part 1 2002 +A2 2008 handy?

[colin todd]

You would not need additional mechanical protection for MI or SWA. They are inherently resistant to mechanical damage.