In this article, Our tips site will tell you why you need a metal sleeve, aka corrugated metal tube for electrical wires. We will find out what metal hoses are, determine the criteria for their selection, and also study the basic rules for wiring in such protection.
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 as a result of 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, corrugated metal pipes are used where the risk of fire is especially high. They are irreplaceable in production halls, industrial buildings. In addition, metal hoses are often used when installing wiring in wooden housing construction, which the portal wrote about in detail. Also, metal cable protection is used in frame houses, in adobe and drywall walls, plastic structures.
There are four types of metal corrugated cable trunks:
- Galvanized. They are not airtight; they are a tube that is twisted from a thin galvanized strip. The joints are sealed with asbestos cloth;
- Tinned tin. They are also not 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;
- Stainless steel. Robust, not afraid of corrosion, can be used in rooms with aggressive chemical environment. Durable and reliable, but quite expensive option for protecting electrical wiring;
- In polyvinyl chloride sheath. Differs in good hermetic properties, is not afraid of moisture, mechanical stress, chemicals. It is quite possible to bury such a corrugation in a trench, leading a cable to the house, and use it 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, which will connect the ends of the pipes;
- A wiring plan is necessary to accurately determine the length of the metal hose, reduce the number of unnecessary bends and connections;
- Before installation, the corrugated tube must be checked for defects, scoring, damage. There should be no dust and 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 hermetic options, and cover the joints with special couplings or electrical tape;
- If you will be doing welding work, protect the metal corrugation during this time, because the metal is thin enough and can be damaged.
Important! When choosing the dimensions of the metal hose for wiring, it must be borne in mind that its filling should not exceed 70% of the inner diameter.
Metal hoses are divided into 12 categories in size, from 5.1 millimeters to 78 millimeters of inner diameter and from 9.8 to 87.1 millimeters of outer diameter. For example: you have a 3×2.5 cable with an outer diameter of approximately 11 millimeters. That is, it needs a metal hose with an inner diameter of at least 13 millimeters. Choose a metal sleeve of category 15 with an inner diameter of 14.7 millimeters – this is the closest to the desired value.
Most often, metal corrugated tubes are sold in coils of 30, 50 and 100 meters in length, 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 need the following fittings:
- Threaded couplings. They have a special scratching nut. Couplings can be straight, angled, with internal and external threads. They will provide additional grounding for the hose. Straight couplings are needed to connect the two ends of the metal hose, and the lead ones are needed for wiring to equipment, a box or a panel. The thread pitch of the coupling must match the pitch of the sleeve;
- Clamps, both plastic and metal. Required for fixing the corrugated tube.