Cables for fire automatic systems.
In this article, I would not like to dwell in detail on the fact that the current regulatory framework clearly requires that the cables used maintain the operability of the system during the entire evacuation period.
In fact, all cables and wires must have the FR (fire resistant) index, confirmed by the appropriate certificate, and be secured with non-combustible materials (this also applies to dowels, which many forget).
This requirement is quite new and not very well thought out yet. It is formulated rather vaguely, and in different ways in different documents (especially if we take into account the non-cancelled fire safety regulations).
If applied literally, this provision even requires the use of fire-resistant wires inside, say, loudspeakers or other products, even if the products themselves are not fire-resistant. And in general, the operability of the system depends not only on the cables.
So, let's leave aside the issue of fire resistance for now, the practice of applying the standards, I hope, will clarify the actual requirements, and there will certainly be many amendments to the regulatory documents. Let's discuss what types of cables are actually used in fire systems. And in the spirit of today, let's discuss what are the opportunities for saving on cable products.
The main cables are the loops for connecting detectors (sensors).
In the case of notification of the 3rd or more types — also cables for connecting the notification.
These are the main kilometers and kilometers of cables, and therefore they often make up the main cost of the system.
The cost of cables depends on the amount of copper in them, i.e. on the cross-section, however, for FRHF cables the price is now often determined by their shortage and is many times higher than similar cables in the usual design. But this is probably a temporary phenomenon.
In the foreseeable future, non-flammable cables will, of course, remain more expensive than ordinary ones, but their price will also mainly depend on the amount of copper.
How can you save on the cost of a cable system?
Addressable systems usually allow you to save a little on detectors, but not much on cable length.
Worse, addressable systems often require the use of much thicker wires or even shielded twisted pairs with standardized wave resistance, and this eradicates all savings.
Moreover, such cables are now almost unavailable in a fire-resistant version.
Many modern addressable systems are less critical to the cable, and for them, as for conventional non-addressable systems, the only limitation is the current consumption.
Good modern detectors consume no more than 200 µA (and some even less than 100), so even when installing several hundred detectors on one loop, it is permissible to use very thin cheap cables.
As for the alarm cables, in the case of alarm types 1–2, addressable systems can provide some savings when using addressable alarms (otherwise, you will have to lay out the alarm wires separately).
Unfortunately, most addressable systems do not provide the ability to connect sufficiently powerful alarms to the addressable line or require increasing the cable cross-section of the entire line, so no savings are achieved.
Significant savings can only be achieved by using alarms (or voice alarm amplifiers) with local redundant power supplies.
In this case, the power cables do not have to be fire-resistant and can run, roughly speaking, from the nearest outlet, and control signals can easily be transmitted via an addressable loop without increasing the cost of its cable.
A separate category of cables is communication cables.
The Ethernet-based systems that have become popular recently are very convenient — new buildings always have a structured cabling system, laid out with a large reserve.
However, this path is closed for a long time for fire systems – there are practically no fire-resistant SCS cables (I mean cables for data transmission of at least category 5).
For classic systems based on the RS-485 interface, this problem is not so acute: if the data transfer rate is 9600–19,200, and the cable length does not exceed 100–200 m, any cable can be used (and not just specialized twisted pair).
If it is necessary to connect system components located at a great distance, then it will be necessary to use fiber optic cables (they are quite available in fire-resistant design).
Finally, power cables.
The requirement for fire resistance here also leads to the need to revise old stereotypes.
If previously a popular solution was to install one central uninterruptible power supply unit and distribute independent 220 V power from it to all components, now it is often more economical to install distributed uninterruptible power supplies.
However, for some systems, such as fire extinguishing pumps or smoke exhaust fans, it is imperative to use fire-resistant cable for power wiring, not only from the control controller to the fan itself, but also from the building input to the control controller.
Such cables are quite affordable, but the range of domestic fire-resistant cables is not very wide yet, it may turn out that for large buildings and powerful loads it will be necessary to use imported cables.
So, although I was unable to completely distract myself from the problem of fire resistance, I still tried to highlight some of the features of cable selection that are becoming important now, when, due to changes in the regulatory framework, familiar solutions are subject to revision and it is necessary to remember again, why certain cables are actually used.