For the technical implementation of fire protection systems, special cable networks based on insulated wiring are used. Communication lines of this type must withstand increased loads in harsh operating conditions, which determines their features. At the same time, wires for fire alarms are available in various versions, which allows direct consumers to individually approach the arrangement of communication networks.
Regulatory documents
In the choice of means and materials for the organization of fire safety systems, one should first of all start from the technical regulations prescribed in the Federal Law No. 123. This Federal Law is of paramount importance as a regulator in this area. However, it does not describe everything.technical nuances of projects of fire safety systems, for which sets of rules (SP) and GOSTs were compiled separately. For example, GOST R 53315 and SP 5.13130.2009 clearly prescribe the procedure for installing and connecting electrical devices. This primarily concerns the selection, laying and connection of wires for fire alarms with target equipment. Moreover, in the new editions of the documents, the emphasis is on the installation and connection of fire automation components under the control of programmable modules and controllers. On the other hand, the basic requirements for the protective qualities of wiring have not changed much.
Wire in the design system
Still, the main task of the cable in the fire complex is to provide power supply and communication between individual functional devices. Therefore, at the basic level, the trace characteristics are calculated for voltage, current frequency, service life, etc. Typical solutions include a wire for a fire alarm 2x 0.5, that is, a two-core cable with a cross section of 0.5 mm2. Such models are able to withstand voltage up to 2 kW at a frequency of 50 Hz, and the time between failures can reach 5000 hours.
On such wires, routes are placed leading to sensors, detectors, annunciators and control equipment responsible for processing signals about signs of fire. Based on the parameters of the room or the building as a whole, individual communication circuits and connection points are calculated. As a rule, for each segment of the connection10-15% is added along the length "in reserve". In addition, in accordance with the regulations, about 10% of the wires for the fire alarm loop should be laid for the implementation of complex laying sections. Most often, these are bypass zones of architectural structures, involving a change in the configuration of the gasket, which cannot be calculated in advance.
Brands of used wires
There are several specialized and appropriately marked types of cables on the market that are approved for use in fire alarm systems. These wires include:
- KPS and KPSE - this is the designation of wiring for mounting fire protection in different configurations.
- KShSE and KShM are specialized solutions for installing fire alarm sensors and mounting alarm loop routes.
- KUNRS is a brand of wire for fire alarms, which is used in the power supply circuits of security devices.
- KSB is a family of interface conductors through which automatic fire protection systems are connected.
- KSBG - flexible wiring for organizing alarm systems in the infrastructure of industrial facilities.
Performance requirements for fire alarm wires
It is not enough that the wire in a fire protection system meets electrical and structural performance requirements. It is important to take into account the specifics of the conditions for the use of such cables, therefore it is essentialfactor in the choice of material is the degree of its external security. First of all, it must be a non-flammable wire. For fire alarms, such products are produced in special shells with varying degrees of thermal protection, which will be discussed below. In addition, such products should be characterized by reduced smoke emission. For example, if we are talking about laying cables on escape routes, then abundant smoke will make the evacuation process difficult. The same goes for toxicity. The same insulation, for example, from polyvinyl chloride often releases harmful substances that, at facilities where a large number of people work, can cause mass poisoning in a fire.
The concept of fire-resistant cable
Since fire is the main threat in the operation of fire protection systems with their components, the fire resistance property deserves special attention. It must be emphasized right away that this is a very specific numerical indicator, expressed by the time interval from the beginning of the contact of the cable insulation with the flame to the process of its combustion. At least this indicator is 30 minutes, that is, the conditional 10 and 15 minutes in the marking mean that the cable is not fire resistant. The most protected non-combustible fire alarm wire has a fire resistance limit of 180 minutes.
Differences in flame retardant cables
It is also necessary to distinguish between fire-resistant wiring and cables that do not support the spread of combustion. In the first case, we are talking about savingthe electrical performance of the circuit in the specified time period, and in the second - the material may lose its functions from the very first minutes of the temperature rise, but in the future, even with group laying, it will not contribute to the spread of the flame in principle.
Types of insulation for fireproof cable
An increased level of protection against thermal effects is achieved through the use of a special sheath in the wire structure. In particular, the following insulators are used:
- Combination of metal and magnesia coating. The cores are placed in a rigid tube made of stainless steel and filled with magnesium oxide. Such a shell does not emit any toxic substances or smoke when in contact with fire.
- Glass mica coating. Winding based on mica-containing components providing an effective thermal barrier. In order to increase structural protection, additional layers based on polymers and rigid PVC plastics can also be used. Theoretically, laying wire for this type of fire alarm is possible in places with a design heat load of up to 750 °C. Under conditions of peak thermal exposure, such an insulator maintains its working qualities for 180 minutes. However, during this time, toxic products and smoke may be released, albeit in minimal volumes.
- Ceramic rubber based insulator. Also a kind of polymer coating with the same protective performance as in the case of glass-mica shells, but with one advantage. Ceramic forming rubberdistinguishes itself favorably with its resistance to various electrical loads, including voltage fluctuations, short circuits, etc.
Design features
Despite the complexity of the external protective coatings, the internal structure of the wire for the fire protection system is quite simple. The working structure of the cable is in most cases formed by two copper cores, which are also covered with special insulation. The technique of twisting the cores into bundles is also practiced, which are then placed in aluminum foil, which protects the conductor from electromagnetic interference. Outwardly, you can recognize the wire for a fire alarm by a red or orange sheath. Moreover, it should be taken into account that such wires can be equally used both for direct data transmission systems and for power supply of fire extinguishing executive bodies.
Fire alarm cable testing
Since we are talking about the use of cables in critical areas, pre-conductors with insulators are subjected to special tests. A typical testing scheme involves applying high voltage to the cable when the alarm is turned on. This is the first step in which the basic function of fire alarm wires is tested without outside interference. At the next stage, the place of conditional laying of the route is heated to critical temperatures of about 700 °C. From this point on, the compliance of the wire with the declared fire resistance limit is evaluated, that is, whether it is capable of transmitting data intime range from 30 to 180 min.
The practice of using fire-resistant cables
Consumers themselves agree that the use of specialized fire-resistant wires increases the reliability of the fire safety system. The problem of fulfilling this task during installation is reduced to economic and technical and structural factors. The fact is that the need for increased protection of the circuit designed to serve the needs of a fire alarm is far from always obvious. Wires for the installation of such systems can be included in common power supply routes with an even higher level of security, and the presence of its own multi-level fire-resistant shell, on the contrary, will become an obstacle to such a combination. Therefore, many people decide to use simpler, cheaper, but no less effective cables. Formally, this will be a violation of the requirements of the regulation, but from the point of view of practical expediency, a differentiated approach to the creation of an electrical communication infrastructure most often justifies itself, therefore, a corresponding change in the standards themselves is not excluded in the near future.
Conclusion
The organization of fire protection systems in any case requires the most complete calculation of operational conditions, on the basis of which a project is developed with requirements for communication networks. As a minimum, the designer must determine the optimum electrical characteristics of the signaling wire.fire, as well as its resistance to possible negative factors of external influence. Moreover, in addition to contact with fire and an increase in temperature as such, it is often necessary to take into account specific threat factors within the framework of certain industries. In industrial production conditions, for example, thermal protection can be supplemented by requirements for resistance to chemical and mechanical stress.
