Fire rated cables not leaving fire compartment

Question

Been asked a couple of questions by an installer and struggling to get a definitive answer from and standards. 
 
 First, if a landlords panelboard contains life safety circuits (in this case both primary and secondary as we have two transformers on site), do the cables between the cut-out and panelboard need to be fire rated if they are in the same fire compartment? 
 
 Second, we have a dedicated DB serving lighting in a fire fighting shaft. The DB has dual supplies via an automatic transfer switch (ATS) in a 2 hour rated enclosure. This enclosure backs onto the shaft so the lighting circuit cables will penetrate the 2 hour rated wall to serve the lighting. Do these cables need to be fire rated throughout, or just where they pass through compartments. Once in the compartment, could they just be T&E? 
 
 The reasoning for both of the above is that once in the compartment, the equipment the cables are serving will not last anywhere near as long as the cable that serves it. But after a good trawl through BS 8519 and BS 9999 and BG70, I can't find anything conclusive. 
 BS 8519 would suggest that any life safety supplies need fire rated cables, so the panelboard supply would need fire rated tails. 
 I would appreciate any guidance.

lyledunn · Accepted Answer

Maybe have a look at 422.2.1 in 7671 with respect to the DB serving the firefighting shaft. Such a shaft is, of course, a protected escape route. 
 Further, my reading of Clause 28 of 9999 is that the lighting in the shaft is required to be maintained by the secondary supply and thus is a safety service requiring appropriate fire resistance. 
 With respect to your first question, I am not sure you will turn up a specific requirement. Rather, the guidance will suggest an objective. In terms of electrical services supplying life safety and fire protection equipment, 37.2.3.1 of 9999 would be a good starting point for a risk analysis.

AJJewsbury · Answer

Not my area at all, but it does occur to me that just because a fire is present within a compartment, it doesn't necessarily follow that the entre compartment is instantly affected. You might have a fire in one corner (where the cables run through) but not (for a while at least) elsewhere in the compartment (where there lights etc might be) - so there might be advantage in having fire rated cables feeding non-fire-proof lights - at least in that it might sometimes buy a little extra time.

- Andy.

mrf · Answer

The answer to your second question is no. Refer figure 1 of BS 8519:2020. The little arrangement in the top left has an ATS in a 2 hour fire resisting enclosure serving life safety equipment in an adjacent 2h fire resisting enclosure. The cables from the ATS which pass through from one enclosure to the other are shown as non-fire-resistant-cabling.

Fire rated cables not leaving fire compartment

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