Types and features of using metal hoses for cables

Regardless of the method of laying the power cable: open (including street), hidden, suspended, it needs high-quality protection. Firstly, the wire itself must be protected from mechanical and chemical influences. Any influence (impact, compression, moisture or aggressively active substances, ultraviolet radiation, heating) reduces the quality and dielectric properties of the insulating coating. Secondly, additional protection protects against accidental contact with the power cable, and prevents the spread of fire in the event of a cable fire.

Therefore, wiring is often laid in an additional sheath - a special sleeve. This can be a plastic or steel pipe with smooth walls, dielectric or metal corrugation.

The last option: a flexible metal hose for the cable, we will look at it in more detail.

A variety of metal sleeves

Depending on the conditions in which the cable will operate, the following types of metal hoses are offered to protect it:

1. Made from galvanized steel strip.
2. For the production of which stainless steel tape is used.
3. In PVC insulation.

Practice shows that at home and on an industrial scale, the most popular are hoses made of galvanized steel. Stainless steel is an expensive item; its scope of application extends to exclusive cable laying areas, where it may be exposed to aggressive chemical environments.

Explanation of markings

In domestic standardization, designations like P3-TsP are used. When deciphering, we get the following information: the metal hose is leaky and made from galvanized steel tape. The letter “P” indicates the presence of a protective shell made of polyvinyl chloride. If an alphanumeric designation appears in the name (for example, ng-25), then the manufacturer wants to say that this product does not support combustion and is even self-extinguishing. Numerical designation – nominal diameter (mm).

Specifications

Coaxial cable: types, scope and installation features

First, let's look at the main parameters of a metal hose made of galvanized steel. The starting material for the manufacture of this type of hose is a galvanized metal plate with a thickness of within three microns. The gap between the turns of twisted plates is sealed:

• cotton fabric for products of the RZ-TsH brand;
• polypropylene film for products of the RZ-SL brand.

The features of this design provide flexibility for the installed cable routes, reliable protection from damage and exposure to dust and dirt, and the option with a polypropylene seal allows it to withstand intense moisture loads. These characteristics allow these hoses to be successfully used when installing both open and hidden wiring. The use of this type of cable protection is recommended in electrical circuits serving ventilation, heating and air conditioning systems. Thanks to the metal shell, which provides a high degree of fire protection, the hose can be used for installing exposed wiring in wood. The metal plate from which the electrical product is twisted serves as a shield and protects the wiring from electrical noise. Based on the material presented, we can highlight the main advantages of the metal hose:

1. Durability and ability to withstand mechanical damage.
2. Ability to provide protection from dust, dirt and moisture.
3. High degree of fire safety.
4. Ability to withstand electrical interference.

Taking into account the needs of electrical installations, manufacturers have mastered the production of a very wide range of internal diameters of metal hoses, from 10 to 100 mm.

Technical characteristics of metal hoses of the RZ-TsKh and RZ-SL brands:

Now let's look at a metal hose insulated with polyvinyl chloride (PVC). Popular brands: RZ-TsP and MRPI. The manufacturing technology of this type of hose and the set of positive qualities remain the same as for previous products. The difference is that they are made with an insulating PVC coating, which provides a higher degree of protection. The presence of an insulating layer classifies this type of metal hoses as a hermetically sealed structure with high resistance to corrosion, which makes it suitable for use in underground communications, tunnels and explosive areas.

It is especially important to know that this type of hose is in no way suitable for working under water, or for laying outdoors in regions with low temperatures. The fact is that the PVC shell is destroyed in the cold

It should be noted that this option has one more important significant advantage - in the event of a breakdown of the cable sheath, the insulating layer localizes the spread of current leakage beyond its boundaries, which will protect service personnel from electric shock upon contact with it.

Technical characteristics of metal hoses RZ-TsP and MRPI:

Classification of metal hoses

I would like to note right away that the first classification of metal hoses for electrical wiring is based on the ability to withstand mechanical damage and loads. Here we see three types of metal corrugations:

— Leaky metal hose (light corrugation). In the notation the series P3. It has thin walls and a leaky design, which do not allow it to be used for hidden wiring under layers of mortar, as well as in places of possible mechanical damage.

Excellent for wiring under ceilings and walls, as well as for open and hidden wiring. The sleeve prevents the cable from bending and protects the room from fire in case of accidents with the wiring.

— Hermetic sleeve of medium strength. Suitable for hidden wiring in screeds, under the plaster layer, in the ground. Series P2.

— High-strength corrugation. Withstands pressure up to 1.4 MPa. Used for wiring with increased safety requirements, including in explosive areas. Series P1.

What is a metal sleeve

A metal hose is a flexible metal pipeline designed to protect cables, wires and pipes laid inside it from premature wear as a result of external influences (ultraviolet radiation, moisture, mechanical damage, etc.).

A metal hose in PVC insulation differs from a conventional one in the presence of a surface protective sheath made of polyvinyl chloride (PVC)

It provides reliable tightness, tensile strength without loss of flexibility, resistance to corrosion and, most importantly, fire safety of the circuit and protection from electric shock.

The schematic structure of a metal hose with PVC insulation is shown in the photo below:

Interesting! The ancestor of the modern metal sleeve is considered to be a necklace made using the gooseneck technique at the end of the 19th century by the jeweler Heinrich Witzemann.

Metal sleeves are used for laying:

• electrical wiring;
• communication lines (telephone, radio and Internet);
• elevator power cables;
• ventilation and heating pipes;
• hoses for air conditioning, ventilation and smoke removal systems;
• transportation lines for bulk products, etc.

Where to choose

Application of metal hose for cable laying

The criterion for choosing the type of metal hose should be the state of the environment in which it will operate.

An unsealed metal sleeve with a cotton seal can be used in interior spaces where the humidity level does not exceed the norm. With a polypropylene seal - indoor spaces with high humidity levels, in bathhouses, laundries, showers, as well as outdoors.

The sealed version with PVC coating is recommended for installation in trenches, tunnels, ventilation shafts, hazardous areas, and underground workings.

The use of metal hoses for electrical wiring made of stainless steel is advisable in rooms with a high concentration of aggressive chemicals, in storage facilities for acids, alkalis and salts.

Important! To carry out installation work on laying cables in a metal hose, you will need a whole list of related devices, such as fastening brackets and couplings that ensure connection and insertion of hoses into distribution devices. Couplings can be straight or angular; they belong to the category of threaded connections with a thread pitch identical to the pitch of the plate turn

Finally, we recommend watching a video review of a metal hose for electrical wiring:

So we looked at the types, sizes and technical characteristics of metal hoses for cables. We hope the information provided helped you decide on the appropriate design option for your own conditions!

It will be useful to read:

• Types and sizes of cable channels
• How to ground a metal hose
• How to stretch a corrugated cable
• What types of cable couplings are there?

Types of metal sleeves

VVG power cable: technical characteristics and application features

Metal hoses are available in various sizes:

• The cross-section diameter varies from 10 to 80 mm.
• The length of the pipes ranges from 10 to 50 meters.

Types of corrugated metal hoses

According to the molding method, the sleeve is divided into:

• Accordion type. It is completely sealed and holds its shape perfectly. It is usually made of stainless steel. It has two serious drawbacks: it is very expensive, and limited in flexibility. Curvature radius up to 20 sleeve diameters. If you bend it too much, it will simply burst. It is used to a limited extent, only for use in special conditions.
• Mass corrugation of turn type. The most common hose: used without restrictions both in industrial facilities and in residential premises. Complex configuration of joints: on the one hand, allows you to obtain a strong, unbreakable pipe, on the other hand, the hose can be bent to small radii. The only drawback is that the coil sleeve is not sealed. If moisture gets inside, it stays there for a long time.
• Corrugated with PVC coating. A polyvinyl chloride sleeve is located on top of the coil spring. Flexibility is reduced, but the pipe becomes completely sealed. The strength characteristics are unchanged: steel coils protect from mechanical stress. Fire safety is also not reduced: flame propagation does not occur in a closed environment.

According to the material of the main shell:

• Mostly, the coiled metal hose is made of galvanized steel. This is a relatively inexpensive material that resists corrosion for a long time. If the corrugation is static after installation, its service life is measured in decades.
• For suspended installation, when the hose can move, it is better to use stainless corrugation. The galvanic zinc coating on the coils does not wear off; the steel is more durable than galvanized steel: such a hose is almost eternal.
• A sealant is placed between the turns to provide tightness and reduce friction. This can be asbestos thread, cotton fabric, or polypropylene film. Of course, 100% tightness is not ensured, but the gasket protects against raindrops and local splashing.

Metal hose design

The metal hose is made of galvanized steel or stainless steel tape, on top of which a protective polymer shell is applied (see Figure 1). The polymer shell ensures complete tightness of the metal hose, protects against harmful environmental influences and significantly increases the tensile strength of the metal hose. The material used to make the polymer shell is listed in Table 2.

A cotton thread is laid between the turns of steel tape for compaction. The metal hose is manufactured in the following versions:

• “P” (increased strength) - made of a thicker metal strip and has a greater tensile strength;
• “HL” (cold-resistant) - operating temperature from -60°C;
• “ECHL” (for extremely cold climates) - operating temperature from minus 70°C;
• “T” (heat-resistant) – metal hose resistant to elevated temperatures, operation up to +200°C;
• “M” (oil and gasoline resistant) - a shell resistant to oil and gasoline (tests according to GOST IEC 60811-2-1-2011);
• “X” - chemical resistance to acids and alkalis;
• “ZG” (rodent protection) is a shell of increased hardness, resistant to rodents, ants and termites. It has maximum abrasion resistance - essential for underground installation. Resistant to ultraviolet and solar radiation. Excellent chemical resistance to many acids and alkalis.

Tips for choosing

To install flexible secure communications, you need to competently approach the issue of choosing a metal hose with an insulating PVC coating:

• The climatic class of the product is taken into account, which is indicated by the manufacturer in the technical data sheet.
• The diameter of the internal cross-section is selected based on the total volume of cables required for installation in the trunk. To do this, the total diameter of the cables is multiplied by a factor equal to 1.5 or 2. The filling of the corrugation should not exceed 70% of the volume of the pipeline.

The pipe material, type of interturn seal and wall thickness must correspond to the operating conditions of the metal hose. Models without a seal or with a cotton inter-turn gasket are intended for indoor use with normal humidity. Asbestos - in conditions of increased fire hazard and the possibility of local heating. Polypropylene - in the ground, outdoors and in conditions of high humidity, incl.

under conditions of direct immersion in water (relevant for models with a high coefficient of tightness).

For laying network cables, the shielding properties of the pipeline are of no small importance, preventing the occurrence of interference on the line. The best performance in this area is achieved by models with an accordion-type connection.

The shielding characteristics of coiled pipes are improved by grounding them. The tightness of the circuit also depends on the number of butt joints. The fewer there are, the better. Therefore, it is better to give priority to corrugations of the maximum possible length.

The markings applied to the pipes and indicated in the model name help to make the right choice:

• MRPI is a flexible metal hose with a polymer coating.
• P1 and P2 are hermetic and explosion-proof hoses, P3 is non-hermetic.
• NG – does not support combustion. PVC insulation made using self-extinguishing plasticizers is usually gray in color.

According to the selected pipes, fittings are also selected, providing fastening of individual sections of the pipeline to each other and a method of fixation on the installation plane (in grooves, on walls, in a suspended state, etc.).

approximate price

The cost of metal hoses depends on many factors: the materials from which they are made, the structure of the polymer, the tightness class, the cross-sectional area, the country of origin, etc. The price is indicated, as a rule, for 1 linear meter, sometimes for a package (coil) 25 or 50 meters long.

Temperature Range

A separate point is to consider the range of permissible temperatures when installing corrugations and cables. For example, the P3-C wire can be used within the range from -40 to +100 degrees. Celsius. If PVC is added to this abbreviation, the range is significantly reduced and ranges from -5 to +60 degrees. However, short-term exposure to elevated temperatures up to +90 °C is acceptable (for example, during installation).

The change in operating temperatures (during operation) is practically within the same limits. The only exception is for the R3-Ts-PVC cable - the minimum level is -25 degrees. Celsius.

What is a metal hose for wires

During electrical installation work, the wiring may be damaged (bent, stretched, damaged by rodent bites, etc.). Protection from negative influences is provided by a metal sleeve, which is divided into the following types depending on the material:

galvanized. Flexible cable channel, not sealed. Using it, they install power electrical networks and cable communication lines. And since it shields electromagnetic interference, it is used when connected to protective grounding. The material of the sleeve is galvanized steel tape with joints sealed with cotton fabric. For a corrugated sleeve supplemented with fabric, the maximum permissible maximum temperature is 3 times lower than for a regular one. At the same time, the product is in demand as it protects against vertically falling drops and UV rays;

Galvanized sleeve

• made of tinned tin. Another common protective element is made of tinplate, which is additionally treated with electrolytic tinning (using tin plating). Distinctive features of such products are long service life and high resistance to rust. This is ensured by tin coating and packaging made of polypropylene, which can withstand harsh operating conditions;
• with PVC sheath. Sealed sleeve type. Using them, they protect wires from mechanical influences, chemicals, UV radiation and moisture. The peculiarity of a metal hose with a plastic shell is that it is suitable for external and hidden installation (the installation location can be channels, trenches, tunnels and even explosive zones). The material of the channel itself is galvanized or stainless steel. PVC coating significantly increases the protective characteristics of the product, including dust and water (provided that sealed connecting elements are used).

Cable channel made of tinned sheet metal

Note! There is another type - stainless steel. Despite its excellent performance characteristics, it is less often used, which is explained by its high price.

Protection of electrical wires

The metal corrugated tube has two very important purposes:

• Protection of the electrical cable from moisture, kinks, damage, electromagnetic radiation and chemical reagents;
• Protecting the building itself from fire resulting from wiring problems. Even in the event of a short circuit and melting of the cable insulation, the metal hose will not allow the flame to spread.

Most often, metal corrugated tubes are used where the risk of fire is especially high. They are indispensable in production workshops and industrial buildings. In addition, metal hoses are often used when installing wiring in wooden housing construction, which the portal Rmnt.ru wrote about in detail. Metal cable protection is also used in frame houses, in walls made of adobe and plasterboard, and in plastic structures.

There are four types of metal corrugated cable ducts:

1. Galvanized. They are not sealed, it is a tube that is twisted from a thin galvanized strip. The joints are sealed with asbestos fabric;
2. Made from tin plate. They are also not hermetically sealed, but before twisting, the tin is protected from rust and external influences using electrolytic tinning. As a result, the metal hose lasts longer and can be used in rooms with high humidity;
3. Made from stainless steel. Durable, not afraid of corrosion, can be used in rooms with aggressive chemical environments. Durable and reliable, but quite expensive option for protecting electrical wiring;
4. In a polyvinyl chloride shell. It has good sealing properties and is not afraid of humidity, mechanical stress, or chemicals. Such corrugation can be buried in a trench when running a cable to the house, and can be used in outdoor conditions and industrial workshops.

We list the basic rules for installing wiring in metal corrugated tubes:

• We must not forget about such important fittings as clamps, brackets, couplings that will connect the ends of the tubes;
• A wiring plan is necessary to accurately determine the length of the metal hose and reduce the number of unnecessary bends and connections;
• Before installation, the corrugated tube must be checked for defects, burrs, and damage. There should be no dust or dirt inside;
• The cable channel is laid without tension, because this will lead to the appearance of gaps between the turns of the corrugation;
• Sagging should also not be allowed;
• There should be no sharp bends;
• For dry rooms, it is quite possible to use the most inexpensive galvanized metal hose; for wet rooms, choose sealed options, and cover the joints with special couplings or electrical tape;
• If you will be welding, protect the metal corrugation during this time, because the metal is quite thin and can be damaged.

Important! When choosing the dimensions of a metal hose for wiring, you need to take into account that its filling should not exceed 70% of the internal diameter

Metal hoses are divided into 12 categories by size, from 5.1 millimeters to 78 millimeters of internal diameter and from 9.8 to 87.1 millimeters of external diameter. For example: you have a 3x2.5 cable with an outer diameter of approximately 11 millimeters. That is, it requires a metal hose with an internal diameter of at least 13 millimeters. You should choose a metal hose of category 15 with an internal diameter of 14.7 millimeters - this is the closest to the desired value.

Most often, corrugated metal tubes are sold in coils of lengths of 30, 50 and 100 meters, but you can get pieces of the required length using tools for smooth cutting of metal products.

To properly install the cable in a metal corrugated tube, you will need the following fittings:

• Threaded couplings. They have a special scratch nut. Couplings can be straight, angular, with internal and external threads. They will provide additional grounding for the hose. Straight couplings are needed to connect the two ends of a metal hose, and lead-in couplings are needed to install wiring to equipment, a box or a panel. The pitch of the coupling thread must correspond to the pitch of the hose turn;
• Clamps, both plastic and metal. Necessary for fixing corrugated tubes.

published econet.ru

If you have any questions on this topic, ask them to the experts and readers of our project here.

Characteristics of the metal hose

To select a suitable cable channel, you should take into account its technical and operational parameters:

• inner diameter. It does not always coincide with the external one, which depends on the shape of the profile. The diameter of the outer sheath of the wire is multiplied by 1.5 or 2, this will be the required sleeve size. If two cables are laid in one metal hose, the diameters are plused;
• conditional pass. Defines the minimum diameter of the profile coil. Connecting and input couplings are selected taking this parameter into account;
• outside diameter. Wave size of the outer turn, if any;
• tightness (according to IP standard). There is a domestic classification (P1-3). Depends on the seal between the turns and what it is made of. This is also reflected in the operating conditions, for example, cotton - for indoor installation (non-aggressive environment), asbestos - at elevated temperatures, polypropylene - for outdoors or in contact with liquids;
• climate class. Now there are about 50 varieties of this parameter available (it is indicated in the sleeve passport);
• ability to pass interference. The best screen is an accordion, but a helical corrugation is also suitable if grounded.

Important! Also, when laying the electrical network, the length of the line is taken into account. You need a length that will allow you to make a smooth bend in the sleeve so that it does not deform.

Characteristics table

Cable laying in a metal hose

The main task of preparing the route of a corrugated pipe is the unhindered pulling of the power or signal cable inside. When planning the installation, it is advisable to provide a seamless circuit. If the length of the section does not allow using a single piece, the correct joint is made using a crimp coupling.

To select a connector, two characteristics are used: nominal bore and outer diameter.

At connecting points, it is necessary to ensure the straightness of the route, the so-called neutral zone. This section should not bend under the influence of external forces. Depending on the nominal diameter, the length of the neutral zone is determined by the table:

There are also couplings and fittings for installing metal hoses into distribution boxes and panels. This hardware solves several problems:

• Ensuring a strong grip on the sleeve: it should not become detached during a longitudinal jerk.
• Creating a certain tightness (if necessary).
• If the box is metal, and it is necessary to ensure uniform grounding of the shell, there must be reliable contact between the coupling, sleeve and box.
• Formation of a smooth flange, against which the cable laid in the metal hose will not be damaged.

The sleeve is attached to the route, depending on the laying method.

• In grooves - on a quickly setting mixture (glue) or clips.
• Open method along the wall - on cable ridges using ties, or on mounting fittings.

• In a suspended state - on cables using clamps. The coil hose cannot be used as a self-supporting hose. With prolonged pulling load, the coils may diverge.

Usually the cable is pulled after installing the metal hose. If there are no bends along the route, this is the best option. A steel wire is driven into the corrugation (if there was none in the new sleeve), and with its help the wire is wound up.

But it is possible to lay the power cable in advance: especially in the case when the hose is bent by 90° after installation. The cut pieces of the hose are laid out on a flat area of ​​ground (or floor), and wiring is inserted into them with a reserve for wiring in the wiring boxes.

After that, the assembled hose is attached to the final devices using fittings and couplings: switchboards, distribution boxes.

Important!

When laying the power cable in a metal corrugation, you should use wires with a double layer of insulation. Although it is somewhat more expensive, it reduces the risk of damage to the insulation when pulled through the turns of the metal hose.

Specifications

When selecting corrugated metal hoses, you should focus on the main technical and operational characteristics:

Pipe inner diameter. It may differ significantly from the external one. When laying one cable, calculate its diameter and increase the value by one and a half to two times to find out the size of the required corrugation. When placing two or more cables, you need to sum up their diameters. Conditional pass. The minimum permissible diameter of turns, which is used as a guide when purchasing connecting elements. Outside diameter. Do not forget that corrugated products have two outer diameters, which depend on the depth of the segments pressed by the rollers. However, the outer diameter refers to the maximum wave size per turn. In the case of smooth-bore pipes, everything is much simpler. Class of resistance to dust and moisture. The international IP classification system or the domestic one can be used - P1, P2, P3, etc. If in the first case, the higher the digital value, the better the protection against dust and moisture, then in the domestic system its decrease symbolizes a deterioration in tightness, but leads to reducing the cost of the product. The tightness is affected by the sealing material located between the turns. Its choice determines the conditions of future operation. For example, cotton is suitable for indoor installation in dry rooms without exposure to an aggressive environment, while asbestos is an ideal option for operation in conditions of increased fire danger (or where local heating of the line occurs). There is also polypropylene - an excellent product for outdoor use or in rooms where the corrugation is directly exposed to any liquids. The climate class must be taken into account when laying along with other parameters. According to this criterion, metal hoses are divided into several dozen varieties. Passing interference

It is important to determine how well the corrugation reflects both incoming and outgoing interference. The best option would be to use an accordion-shaped pipe, although coiled products with proper grounding will be no less useful and of high quality.

Advantages and disadvantages of sleeves

Metal hoses used for laying cables have the following positive qualities:

• increase the service life of electrical networks;
• can be installed without the use of special tools;
• highly durable, resistant to rodents;
• protect from mechanical damage, precipitation, chemicals;
• fireproof (does not support combustion);
• using a variety with a PVC sheath, provided there is reliable grounding, protection against electric shocks increases significantly;
• if necessary, a section of the chain can be easily and quickly replaced;
• made of flexible material;
• environmentally friendly;
• turns and bends do not cause internal stresses or deformations.

Product with protective PVC coating

The product also has characteristic disadvantages:

• price;
• complicates installation and prolongs installation time;
• not suitable for places where moisture accumulates (the insulation may deteriorate).

Note! The disadvantage associated with the limitation of installation in places with high humidity is solved by installing a drainage system at the lowest point of the network. An effective way to protect wiring

An effective way to protect wiring

How does a metal hose work?

The invention of corrugated metal hoses is considered to be a revolutionary discovery, thanks to which the level of safety when laying cables has significantly increased, and additional options have appeared for organizing hidden wiring. Compared to conventional smooth-walled pipes, corrugated products have several undoubted advantages. These include high strength (reliability), flexibility and lower weight.

By placing the cable in the ground, depending on the depth of the trench, you place a serious mechanical load on it. It is known from the laws of physics that the larger the area, the less the pressure exerted on it. Smooth-walled structures are noticeably narrower than corrugated, which leads to a reduction in the load level per linear meter.

However, this approach has certain nuances. When laying a cable in the ground or screed, you must ensure that the earth or cement-sand mortar adheres as tightly as possible to the protective shell. Ignoring this rule can lead to increased deformation due to the presence of voids that disrupt the uniformity of load distribution.

How metal hoses are made

The production of corrugated metal hoses is divided into several stages. To begin, select a sheet of steel that can withstand the potential operating conditions. The thickness of the workpiece, which is subsequently rolled into a thin-walled pipe, varies between 0.2-0.3 mm. To connect a series of steel sheets, flat convex or concave washers with bolts are used.

Argon welding allows you to fix a cylindrical shape, while this process takes place on automatic lines that include laser systems. The latter are necessary for quality control of the welded joint (seam). The main condition is that the width of the seam should not exceed the thickness of the steel sheet. Next, the product is galvanized to improve its anti-corrosion properties. Stainless steel is better suited than others for the production of corrugated metal hoses, as it increases the tightness, reliability and resistance of the product to chemically active environments.

The segmented plane is formed under pressure from rollers, which are selected depending on the desired configuration and diameter of the pipe. In general, the final product has two diameters - minimum and maximum, which depend on the size of the segments. The narrowing of the diameter is insignificant and is achieved by reducing the wall thickness. This is due to the increased flexibility of the metal hose. This property eliminates the need to use fittings and other products to turn and avoid obstacles on the cable route.

Classification of metal hoses for laying electrical networks

Corrugated metal pipes, depending on their resistance to mechanical loads, are divided into three types:

1. Lightweight with increased flexibility and low mechanical strength. Installation and operation of these products is possible if one important condition is met - there is no load on them. An excellent option for installation under false ceilings or sheets of plasterboard.
2. Heavy with good mechanical strength. Such products are suitable for hidden installation in the ground, screed or under a layer of plaster.
3. Extra heavy with maximum mechanical strength. These hoses should be used in conditions of increased safety requirements. For example, when laying communication lines in public places with a large flow of people (educational institutions, metro, hospitals).

The above example of corrugation classification is simplified, since the load-bearing range is very large and can reach 4000 N/cm2.

Depending on the shape of the internal section, pipes are divided into round and ellipsoidal. The latter are used in telecommunication tunnels.

Galvanized hoses can be equipped with various materials that increase the tightness of the products. The following varieties can be distinguished:

• ordinary corrugation - without seals, not airtight, flexible, retains high strength (withstands temperatures up to 300 degrees Celsius);
• with cotton seal;
• with a moisture-proof sleeve made of polyvinyl chloride - provides protection against moisture and leakage currents, but the ability to withstand high temperatures is halved.

Important! The maximum permissible temperature of corrugated hoses with cotton thread is three times lower than during operation of conventional hoses. On the other hand, such a product is resistant to ultraviolet rays and vertically falling drops.

Advantages and disadvantages

We list the main advantages when using metal hoses in cable routes:

• increasing the durability and service life of the electrical network;
• ease of installation - no need to use special devices;
• high strength, preventing damage by rodents;
• resistance to precipitation and exposure to chemically active (aggressive) environments;
• protection against mechanical shocks;
• does not support combustion;
• when using PVC insulation and due to reliable grounding, a high level of protection against electric shocks is achieved;
• possibility of prompt and error-free replacement of a section of the cable chain;
• high flexibility;
• when turning and bending, the specified cross-section of the corrugated pipe is maintained, the appearance of internal stress and the formation of microcracks leading to a violation of the integrity of the protective shell are eliminated;
• environmental Safety.

In addition to the high cost of products and an increase in the budget when laying electrical wiring, two more points can be attributed to the disadvantages of using metal hoses:

• complication of installation and increase in cable laying time;
• the need to avoid the accumulation of moisture on the surface or near the hoses, which can lead to insulation failure.

Important! The last drawback can be eliminated easily and simply by placing a special drainage system at the lowest point of the structure.

Types and characteristics of corrugated pipes

Types of corrugated pipe

A corrugated pipe is a pipe with stiffeners. This allows it not only to carry heavy loads, but also to have a certain flexibility.

Such properties of corrugated pipe have allowed it to become widespread not only in the energy sector, but also in other areas of the national economy.

So:

• Nowadays, corrugated PVC pipes of various levels of fire resistance and metal pipes are widely used. For electrical wiring, pipes made from both materials are used.
• At the moment, the industry produces metal corrugations for electrical wiring with diameters of 16, 20, 25, 50 and 63 mm. In this case, the outer diameter of the pipe is indicated. The internal diameter depends on various parameters and is usually indicated using a fraction sign.
• To lay the wiring, you should rely specifically on the smaller internal diameter. After all, it is he who indicates the cross-section available for laying the cable. It is worth noting here that for installation you should take pipes with an internal diameter significantly larger than the diameter of the wire.
• Corrugated pipe is supplied in coils of different lengths. These can be bays ranging from 15 meters to 100 meters long.

Metal corrugation is supplied in coils

Characteristics of metal corrugated pipe

Metal corrugation for electrical wiring can have different characteristics and this should be taken into account when choosing and installing.

All of them can be seen in the labeling of foreign products. Unfortunately, not all domestic manufacturers have also adopted it.

So:

• Depending on their resistance to external loads, corrugations are divided into:
  Very light – load up to 125N/cm2,
• Light – load up to 320 N/cm2,
• Medium – load up to 750 N/cm2,
• High – load up to 1250 N/cm2,
• Very high – load up to 4000 N/cm2.
• Corrugation is also divided according to impact strength. These can be values ​​from 0.5 kg/100 mm to 6.8 kg/100 mm.
• Corrugations also differ in nominal temperature. So the minimum temperature can vary from -45°C to +5°C. The maximum temperature can range from +60°C to +400°C.
• Well, the last, but perhaps one of the most important, is the flexibility parameter of the corrugated pipe. It can be rigid, flexible, extra flexible or flexible with memory effect pipe.

Symbol when ordering an additional nut TU1690-020-45416838-2008

1 - metric thread M according to GOST 24705-2004 (ISO 724:2003) with a pitch of 1.5.2 - NPT thread corresponds to the Russian thread standard K (GOST 6111-52, tapered inch with a profile angle of 60 degrees).3 - are provided for reference, the manufacturer may change dimensions without prior notice.4 - the permissible pipe diameter for the pipe connector is indicated in table 4

How and where to use it correctly

Incorrect installation of electrical wiring can lead to disastrous consequences, so you should follow simple recommendations:

• first of all, a wiring plan is drawn up (markings are made, all bends and irregularities are taken into account);
• Before using the hose, it should be checked. There should be no nicks or deformations inside that could damage the cable or prevent it from being inserted into the tube;
• The metal hose does not need to be stretched, otherwise its strength will decrease. The likelihood of gaps forming between turns also increases. A similar rule applies to sagging;
• if wiring is done in a damp room, you will need a sealed tube (in this case, the connection points are additionally protected with insulation or couplings);
• for dry rooms use galvanized, non-sealed cable ducts;
• sharp bends can damage the cable and the corrugation itself, so you should not allow them;
• the corrugated tube is made of thin material that can be damaged during welding, which must be taken into account when carrying out such work;
• in wooden houses, instead of corrugated pipes, it is better to install cables under plaster (this method is also called open).

Important! For open wiring, plastic corrugated tubes, only those made of non-flammable material, are suitable. Hidden electrical wiring in a frame house

Hidden electrical wiring in a frame house

A metal hose is a good option for laying both open and hidden electrical wiring. It’s just that it requires grounding and costs 7 times more than plastic corrugation. It is for this reason that it is more relevant for serious networks, but also finds application in residential buildings (basements, workshops).

Installation features

Finally, let’s look at the features of installing wiring in a metal hose. Let’s not invent anything, but read the Rules for the Construction of Electrical Installations.

According to clause 2.1.4._2, a flexible metal hose is used for hidden electrical wiring in plastered grooves, under plaster, as well as in building structures during their production.

Further, in clause 1.7.76_4, we read that metal hoses must be grounded, since electrical hoses are subject to requirements for protection against indirect contact.

And one more point 1.7.123. You cannot use a metal hose as a PE conductor.

Operating principle

Corrugated protective shells are a breakthrough in the field of engineering communications. They increase the level of security of networks and open up new possibilities for hidden installation. Durable metal - a reliable and durable outer shell that is flexible, not heavy, and protects better than plastic.

If the cables are laid in the ground, the sheath has to experience increased stress. The soil pressing on the corrugation has less mechanical impact, since the stress is distributed. This allows you to significantly reduce the load per unit surface (compared to a smooth tube).

Note! There is one subtlety here - when laying the cable in the ground or screed, it is necessary to ensure that the soil adheres tightly to the surface of the sleeve. Voids lead to increased strain levels

Cables must be protected to avoid unpleasant consequences

Scope of application

In accordance with the rules for electrical installations, the wiring must be laid in a special sleeve. It can be made of plastic or steel with smooth walls, as well as metal or dielectric corrugation. The product must be used when laying cables in buildings made of flammable materials - foam composites, plastic, logs, beams, SIP panels. Flexible metal hose is used only for open wiring. When it is closed, a solid steel pipe is used.

If the cable is laid in insulation or insulation, then it must also be protected with a sheath. This applies to walls that are regularly exposed to moisture, as well as outdoor and suspended installations. A metal hose is used in rooms where there may be frequent temperature changes - in baths, boiler rooms, saunas, heat treatment shops and kitchen blocks.

The material is used for laying cables in buildings with high mechanical risks - at sawmills, workshops, car service centers and metalwork shops. A metal pipe is used underground; it is also necessary in cases where it is necessary to carry out unauthorized work.

Main characteristics

The metal hose is made of galvanized, stainless, tinned steel or aluminum and covered with a layer of elastic plastic in black or gray. The modular pipe system prevents the formation of microcracks in the body when bending.

• The steel structure and PVC coating belong to the class of fire-resistant, self-extinguishing materials that do not support combustion.
• The PVC layer acts as a dielectric.
• Working pressure – 0.5-1.4 MPa.
• Maximum temperature: 300⁰С (for modifications without seals and with an asbestos layer);
• 100⁰С (for models with a cotton layer).