Types and application of metal hoses for cable laying

Installation and laying of electrical wiring is accompanied by equally important additional processes, such as marking and installation of protection. The most effective product for increasing resistance to mechanical stress is a metal hose for cables.

This device fully meets the expectations of installers and is often used as the main protective element for electrical systems in wooden houses. The sleeve is easy to install and operate; wiring can be pulled through it without resorting to the use of special devices, and the risk of bending the cable inside it is minimized.

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.

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).

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.).

Specifications

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

1. 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.
2. Conditional pass. The minimum permissible diameter of turns, which is used as a guide when purchasing connecting elements.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.

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).

On a note! Unlike rigid metal hoses made of solid sheet metal, flexible pipelines do not change the configuration of the internal passage when bent.

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.

Types of metal sleeves

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.

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).

How to choose a metal hose?

When choosing a metal hose for laying cables and wires, you should be guided by the following criteria:

All metal hoses are measured by internal nominal diameters DN (DN). DN is a standardized designation for internal diameter. Nominal diameter DN, nominal diameter, nominal bore, nominal size, nominal diameter, nominal bore, internal diameter. All these concepts mean the same thing. The unit of measurement for diameter is length. For the Russian standard, the internal diameter is measured in mm. Based on this, having information about the brand and outer diameter of the cable, a metal hose is selected according to DN. It should be taken into account that the filling of the metal hose with cable or wire should not exceed 70% of its internal diameter.

Example: the outer diameter of a 3x2.5 cable is 10.3 mm. Accordingly, to lay this cable, it is necessary to use a metal hose with an internal diameter of at least 13.5 mm, which corresponds to a metal hose with 15 mm.

For a more accurate selection, you can use special correspondence tables presented in technical reference books.

Metal hose parameters

Also, when choosing a metal hose, one more parameter should be taken into account - the length of the line being laid. It is necessary to choose a metal hose of such a length that will allow you to create a smooth bend in the cable line and ensure its integrity. Otherwise, it is necessary to use special fastening elements - fittings that allow connecting sections of metal hose to each other, as well as to other products (electrical wiring pipes). It is clear that with short lengths there is no need for this, however, most often (especially on an industrial scale) the construction length of the cable coils exceeds the length of the metal hose coils and connecting fittings (fittings) are used to improve the quality, durability, convenience and aesthetics. Fittings such as metal hose-metal hose, metal hose-pipe, metal hose-shield are intended for connecting and inserting metal hose into equipment.

All information about the technical properties of the metal hose: type, internal and external diameters, coil length, tensile strength, weight and dimensions, fittings for connecting the metal hose (fittings) can be found on our website, as well as in the accompanying documentation.

The electrical fittings plant produces metal hoses in PVC insulation, as well as without insulation, of various diameters and designs.

Compatibility of SD/SO staples with metal hose

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Installation rules

We list the main recommendations and conditions that are important to fulfill before installing an electrical cable in a corrugated metal hose:

1. At the first stage, you need to create a diagram of the future cable route, and then mark it. Thanks to this, you will calculate in advance all the bending angles and other features of the line.
2. Inspect the purchased product and make sure there are no mechanical damages.
3. There should be no traces of dirt on the outer and inner surfaces.
4. Before installation, remove any unnecessary elements - transport film, fasteners, etc.
5. Be careful and attentive at all stages, but especially when unwinding the corrugation in the bay. Do not overtighten it, as stretching can significantly reduce its strength.
6. Professional specialists are required to select and install corrugated products. The above information is good for guidance purposes only, but the final decision should be made by a qualified installer based on specific conditions.
7. Avoid sparks from the welding machine, which may damage the product. Moreover, if there was dust inside the sleeve, a fire may occur.
8. Check the integrity of the corrugated pipe again upon completion of installation, as you did before this process.
9. If welding is required during the installation of the cable route and laying wires in the corrugation, then care must be taken to protect the metal hose from overheating.

Cable laying in a metal hose

The main task that needs to be solved before installing a corrugated pipe is to make sure that there are no obstacles when pulling the power cable. When planning the laying, try to create a line on which there will be no unnecessary joints. If the length of the section is too long and it is impossible to use a single piece of metal hose, then you can make the correct joint using a crimp coupling. When choosing a connector, you need to focus on the nominal bore and outer diameter of the product.

All junction points must be located on a straight route - in the neutral zone. No external forces should exert any load or cause bending.

The table below shows the dependence of the length of the neutral zone on the nominal diameter:

To insert a metal hose into a distribution box or electrical panel, you need to use couplings and fittings. This fittings are necessary to solve several problems:

1. Increased strength when gripping the sleeve. The load during a longitudinal jerk should not break the connection.
2. Improving tightness (if necessary).
3. If a single grounding of the shell and metal box is required, then it is important to monitor the quality of contact between the coupling, corrugation and shield.
4. Elimination of differences at the joints, which could lead to difficulties during cable laying.

The sleeve fastening depends on the cable laying method:

1. Grooves are fixed with adhesive or clips.
2. Open wiring on the wall - fastening is carried out with special cable racks with ties or mounting fittings.
3. Suspended state - cables with clamps. The coil corrugation cannot be used as a self-supporting corrugation, since the coils may diverge due to prolonged load under its own weight.

The wire is pulled after installing the metal corrugated pipe. This is ideal if there are no bends in the route. In this case, a steel wire is pulled through the corrugation (some manufacturers sell a metal hose with wire), to the end of which a cable is attached.

If the cable line bends at an angle of about 90 degrees, then it is advisable to pull the wire in advance. To do this, lay out the components of the corrugations on a flat surface in a straight line, run the cable, leaving a reserve for disconnection in the mounting boxes. Next, the hose is assembled and attached to panels and distribution boxes using couplings.

Important! When installing electrical wiring in a metal corrugated pipe, ideally you should use a double-insulated cable. This will increase the cost of network production, but will reduce the risk of damage to the insulation during the process of pulling the wire along the turns of the sleeve.

Metal hose grounding process

The protective case is secured using a high-quality and durable bracket. Before performing this action, you need to thoroughly clean the area of ​​the girth. Next, a grounding screw is attached, which is connected to the bracket with a jumper. As a jumper, you can take a copper wire with a diameter of at least 4 mm. In accordance with the PUE, make sure that you do not pinch the metal hose and avoid stretching and twisting.

Metal sleeve protection

Manufacturers of metal hoses produce two types of products - with and without a protective shell. The first is designed to increase the level of fire and electrical safety and prevent the ingress of moisture, dust and dirt. Due to the shell, the service life of the corrugation and the cable laid inside it significantly increases.

By the way, an insulated metal hose costs much less than a wire or cable that has additional protection. The most effective and efficient to use is the PVC sheath, designed to protect against leakage currents.

The use of metal corrugated pipes when laying various communications and cable routes is not always justified. If, with hidden wiring, the useful properties and qualities of the metal hose are realized in the best possible way, then when the lines are placed openly, it is advisable to use protective elements made of other materials approved by the PUE. It is more expedient and economical.

Metal hose for cable: dimensions, technical characteristics, photos

Metal hose for cable: dimensions, technical characteristics, photos

First of all, it is necessary to answer the question regarding the structure of the metal hose and the materials for its production. In this case we are talking about an elastic, sealed and corrugated high-pressure pipeline, which is produced using galvanized tape. This metal sleeve provides the cable with additional protection. It is important that the wires are not squeezed or pulled. It must also be insured against cuts, electromagnetic radiation and other negative environmental influences.

The method by which such products are produced is not complicated. That is why prices for metal hoses are not high. A company with any financial capabilities can purchase them. An ideal option for saving on the possible repair of communication systems if the network is broken.

Basic properties

Among the main features of the metal hose, the following should be highlighted:

· Radiation safety;

· Resistance to fire;

· Explosion safety;

· Chemical safety;

· Electrical safety.

Application

During operation, the properties described above always appear. The same applies to storage and transportation issues. Metal hose can be used in a variety of fields (oil industry, gas industry, construction, etc.). Petroleum products, food and chemical substances are not dangerous to its walls. Operation is provided in the following temperature range: from -200 to +700ºС. The product can withstand pressure of 306 atmospheres.

The most important thing when choosing a metal hose is to decide on the size. Currently they produce models with sizes from 6 to 200 mm.

Specifications

Metal hoses are produced in accordance with strict technical standards. The product is based on PVC-sheathed tape or galvanized tape. In the first case, the walls of the model will be black. Metal hoses are produced with different degrees of protection. If we are talking about the IP65 marking, this means that the cable will be protected from dust and water getting inside.

Temperature Range

When carrying out installation work, it is extremely important to take temperature into account. The temperature range for cables marked RZ-C is -40 - 100ºС. For RZ-Ts-PVC cables, this value ranges from -5 to +60ºС. At the same time, installation work at a temperature of 90ºС is also permissible.

The operating temperatures are approximately the same. Important note: if we are talking about RZ-C, the PVC sheath will reduce the temperature range to the following value: from -25 to +60ºС. Remember that the described metal hoses do not support combustion.

Distinctive features

The list of distinctive features of the described metal hose includes the following:

· Available in the form of a bay;

· There is a PVC shell;

· Provides additional protection for cables from various mechanical impacts;

· Can act as an additional screen;

· Can be used in areas where transportation of large-fraction bulk solids is necessary.

This metal hose is often compared with models made of HDPE and polyvinyl chloride. Its main advantages: powerful protection of cables from shocks and fires. Rodents will also not be able to damage the metal hose.

The described product often acts as a screen (protection from electromagnetic influences). The PVC shell is an excellent insulator that prevents moisture and dirt from getting inside.

Metal hose is produced in coils. The length can be from 10 to 100 meters. Marking also implies external (from 11.6 to 83 mm) and internal (from 7.8 to 78 mm) diameters. The nominal diameter range is from 8 to 75 mm.

Design features

The metal hose is distinguished by its versatility. Such products are often used during installation work related to the installation of heating, air conditioning, and exhaust ventilation systems. If the metal hose has PVC insulation, then it can be used to provide protection against electric shock during leaks.

The metal hose described here is made from galvanized steel tape. In some cases, it is covered with PVC insulation. Metal hose colors: black, gray In the latter case, the model will be non-flammable (this is ensured by certain chemical elements contained in the composition).

Various enterprises produce metal hoses with a high level of fire resistance. In the event of a fire, such products extinguish (the basis of the insulation is a plasticizer). During production, the shell is applied to the model, which comes with the marking RZ-TsH. Protection from external damage is present. Before installation work, all hoses should be carefully checked. They should not have any defects. The minimum bend radius is also checked. If the sleeve bends more, it is considered defective.

Explanation of markings

RZ-CP is a non-hermetic hose made on the basis of galvanized steel tape. Includes a PVC coating (indicated by the letter P). If the marking contains a value of -25, this means that the product does not support combustion. The number indicates the diameter of the conditional internal passage.

Installation features

The metal hose for the cable (GOST R 51330) is laid in accordance with special technology. When this is important, aesthetic characteristics are taken into account. However, most often the products described are used for installing wiring in warehouses, garages, industrial premises, etc. A closed or open wiring arrangement is possible.

During installation work, staples are often used. They are fixed using self-tapping screws. It is also not uncommon to use clamps. The metal hose does not protect cables from fire. That is why laying cables on surfaces that are flammable is a gross violation.

Power wiring is laid only in situations where the hose is surrounded by fireproof material. During installation work, it is important to exclude the following: moisture (including condensation) should not accumulate on the surface. Connecting and input couplings act as protective fittings. The hose can be brought out into the installation box (input couplings are used).

Conclusion

At the moment, the described products are used very widely. The list of reasons for this popularity includes the following:

· High level of wiring protection from various mechanical damages;

· High level of fire protection;

· High level of flexibility;

· Easy to install. No additional accessories or fixtures are required for installation work;

· Protection from unwanted cable kinks;

· Protection from mice and other rodents.

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