How to choose a metal hose in PVC insulation: table of types of shells, markings and prices

Welcome!

Today it is difficult to imagine a house without electricity, telephony, Internet, television and other benefits of civilization. Behind this prosperity are billions of kilometers of cable and wires laid on and under the ground, inside and on the surface of the walls of buildings. Special boxes and metal hoses, in particular metal hoses in PVC insulation, help to minimize the aggressive impact on the environmental highway. This is what we will be talking about in today’s review.

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.

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.

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.

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.

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.).

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).

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.

Metal hose diameter tables.

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