- Fire safety standards
- Correct compilation of SKL
- Alternative methods of fire protection
- Installation of installation products inside the PPS
- Open wiring option
From the article you will learn why the installation of electrical wiring in walls covered with expanded polystyrene is associated with a high degree of risk and how to prevent possible negative consequences. We will tell you about fire safety standards, give advice on the installation of cable lines and wiring accessories.
Undoubtedly, expanded polystyrene (PSP) made a revolution in the field of building and insulation materials, but its use makes the construction object super-category in terms of fire safety. PPP is not only highly flammable and burns very quickly at high temperatures. The main danger to human life is represented by highly toxic combustion products: a few breaths are enough for a lethal outcome..
The installation of wiring in the PPP is also closely related to the difficulties of fixing and bricking cable channels: in soft and loose foam it is often almost impossible to firmly fix the socket and junction boxes. How, with such an abundance of difficulties, to electrify objects built using fixed formwork?
Fire safety standards
The main fire hazard is short circuit and heating due to prolonged overloading of cable lines. The only effective protection for the cable is an all-metal sheath – a steel pipe with a wall thickness of at least 1.2 mm. This is due to the requirement for a high localization capacity of protective shells. The fact is that the peak value of the current during a short circuit reaches 2000 amperes, while at the place of breakdown at least 3 kJ of thermal energy is released. This is quite enough to burn through a corrugated tube and even a metal hose.
In addition to the cable, all wiring accessories also need protection: sockets, switches, etc. Fire can be avoided by bricking the installation boxes with abundant use of gypsum binders. Naturally, the presence of connections on the cable inside the channel is completely excluded, the sections of the wiring between the inspection points must be solid. Consider the basic requirement for hidden cable routing: the bending radius must be at least six conductor diameters.
The situation is complicated in cases where the construction object is a municipal institution, residential or administrative building and requires acceptance before being put into operation. Consequently, the package of acceptance documents must include an act for hidden electrical work, and no conscientious contractor will issue it without observing all real precautions.
Correct compilation of SKL
In order to minimize the work on fire protection, it makes sense to think about drawing up a complete project for the internal power supply, and, first of all, a section of the structure of cable lines. The main goal of the project and the main specification should be to minimize the installation of wiring inside the coatings from PPP by any means, even if this causes a moderate increase in price. Here’s how you can do it:
- Avoiding horizontal cable routing along walls.
- Installation of cable products in a cement floor.
- Installing sockets on both sides of interior walls (walk-through).
- Complete or partial absence of junction boxes.
- Laying of cable ducts in the thickness of concrete even at the stage of pouring the walls.
The last solution will be possible only when drawing up a high-quality construction project with a well-developed electrical part.
Alternative methods of fire protection
Of course, not only “solid” insulation of cable lines can provide full protection against fire. The quality of cable products plays a huge role. Conductors of brands PVA, SHVVP, PUNP and the like are strictly prohibited to be used even when laying on non-combustible grounds. And in the case of PPP, their use can be a fatal mistake. It is allowed to lay only VVG ng LS cable, and the products must be certified in accordance with the standards GOST 12.1.044–89 and 16442–80, as well as the DBN standards of the corresponding structure category. It is equally important that the manufacturer has international product quality certificates such as IEC 60331, IEC 60228 and IEC 60245.
The electrical system of the building must have a reliable ground loop, tested by an electrical laboratory. The main parameter – resistance to current spreading – should not exceed 2 ohms. The type of grounding system is TN-S, the power supply circuit for single-phase consumers is three-wire, for three-phase – five-wire. All protective metal shells must be connected to the protective conductor, while a current leakage protection device is installed in the main switchboard. In the event of a breakdown of insulation to a grounded shell, a current leak will inevitably occur, so the power will be disconnected within one half-period, which is too little for metal burning. In this case, the use of a metal hose of proper quality is considered acceptable..
A third method of protecting against fires is to install reliable and properly calibrated protective devices. First, it is necessary to draw up a complete map of loads and determine the maximum current values for each line, taking into account inrush currents, daily and instantaneous voltage drops. The permissible class of trip units of the circuit breaker is B, while the value of the trip setting should not exceed 1.3 of Inom. Today, the best quality of protection is provided by microprocessor-based trip units controlled by digital network analyzers. Such equipment unmistakably detects the presence of a short circuit even before the current reaches its peak values and switches off almost instantly..
Installation of installation products inside the PPS
Expanded polystyrene is a rather loose material, so the installation boxes fixed in it loosen over time and fall out. Therefore, it is recommended that the sockets be secured to an existing solid base. It is very important to mark in advance the location of the concrete pillars in the walls of the “thermal house” using steel wire poles. Then you can choose two mounting options.
With a PPS thickness of less than 5 cm:
- Cut off some of the foam at the installation site, exposing a solid backing.
- Apply alabaster on the supporting layer with a layer of at least 2.5-3 cm.
- Install the socket outlets, aligning them along the plane of the wall and abundantly coated with alabaster.
- Allow the composition to completely solidify.
- Reinforce the “pull-off” fastening with two quick fixing plugs using wide washers.
If the PPP layer is thicker than 5 cm:
- Cut a 10×10 cm niche in the foam.
- Replace the cut foam with a block of aerated concrete of the appropriate size and depth.
- Fix the block with ceramic tile adhesive, pre-treating the base with a primer.
- If necessary, reinforce the fastening with quick fixing plugs.
- Install the socket using the standard method.
If the inner walls of the house are covered with gypsum plasterboard, there will be no difficulties with mechanical strength, but each socket box must be surrounded by a layer of refractory material. In residential premises, asbestos fabric cannot be used; instead of such insulation, glass tape or plastering with stucco is perfect..
Open wiring option
If the aesthetic aspect does not bother, you can avoid fire safety problems by installing open or combined wiring. For example, by hiding the main wiring lines in the floor, and laying the outlets for sockets and switches in decorative plastic cable channels. Manufacturers such as Hager and Schneider-Electric have a whole series of products of this type, allowing you to lay the wiring in the open without significant deterioration in appearance..
With open wiring, it is important to have a refractory layer of at least 1–2 cm, it can be plaster or gypsum plasterboard with an air gap. There are also additional requirements for cable products. In residential premises and public buildings, only smokeless cable brands are allowed: VVGngd, VRGng-FRLS or FRHF, as well as NYM.