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Posted By Topic: Fire Alarm Cable

dmelectrical
Nov 21 2018 13:07

Just had a fire alarm guy run his call point cable (which runs at 24VDC) in the same holes as my power circuit as he didn't want to drill his own. When I mentioned segregation he said it's fine as his cable rated at 230VAC?
   

gregmcc
Nov 21 2018 13:25

3.9.8.3.....(b)
all cables or each conductor of a multi core cable shall be insulated for the highest voltage present.

So yes, but if in doubt have a look at the marking on the fire cable to see if it actually is rated for 230V.
Something to keep in mind, if it's a multiphase installation it may need to be rated for 400V if the fire cable is run next to a multiphase cable.

   

AlecK
Nov 21 2018 14:31

3.9.8.3(b) applies only to conductors within a multicore cable, so not relevant.
In fact the whole of 3.9.8 relates to conductors in the same wiring system.

In this case there are 2 separate multi-core cables, one being all cores LV and one being all cores ELV. Two completely separate wiring systems. So the clause does not apply, and the voltage rating of the F/A cable doesn't matter.
It would if they were individual wires in a trunking, or if one multicore is carrying several different services. Also if the FA cable is present where the LV cable's sheath has been removed, then the V rating of the other cable would matter.

However most F/A cable is standard TPS, just with a different sheath colour; so the V rating will be fine. Being multiphase make NO difference, as the voltage to earth is exactly the same. There simply cannot be any more than 230 V between any of the LV conductors and the F/A conductors.
Both are double insulated for 230 V, and only the LV one has to be.

Unlike data, there's no need to avoid mere proximity. With data, being too close and especially running parallel can cause interference with data due to EMR from the electric cables, but the F/A circuits are generally a simple resistance circuit.

The only negative effect would be that the extra cable in the hole could limit the ability of the LV cable to move to be > 50 mm from wall surface. That would be enough reason to say: "Don't use those holes".



   

dmelectrical
Nov 21 2018 15:48

Thanks. When I mentioned I was not thrilled with the idea of his cable he did point out that I was a pedantic dickhead which sort of soured the discussion.
   

gregmcc
Nov 21 2018 17:00

AlecK,

3.9.8.3 (B)

starts with "All cables or each conductors of a multi core cable"

So it is relevant. and it's about segregation of services, one of the means is by ensuring that one of the criteria are met, segregation by distance, by barrier and so fourth.




   

AlecK
Nov 21 2018 17:43

start at the beginning, before concentrating on a sub-para .

The first para is about HV vs LV & ELV not being in "same wiring system".

Para 2 then covers LV vs ELV , again only where in "same wiring system". And the (a), (b), & (c) bits are all sub-parts to para 2.

Theree's no definition of "wiring system" in Section 1, but it's effectively defined in 3.2 "types of wiring systems", which takes us to Table 3.1.

So this case isn't about 2 different services in "same wiring system" it's about 2 services each having its own completely separate "wiring system". One is LV, the other is ELV (but happens to be in cable rated for LV).

And there's absolutely nothing there about having to segregate different wiring systems.

So since the situation doesn't meet the trigger condition of "in same wiring system"; NONE of the following options needs to be taken; ALL can be ignored.




   

SymonS
Nov 21 2018 22:30

... which is helluva long winded way of saying, Yes, youre correct gregmcc, there's no issue with it.