Direct twisting of copper veins of different diameters creates point resistance, which instantly turns the contact site into a local source of heating and potential fire. Unlike standard connections, where the parameters of conductors coincide, the joint heterogeneous wire requires strict compliance with engineering standards, since the current passing through the thin vein will exceed the permissible loads for its cross section, if correct switching is not applied. Ignoring the physics of the process when building up a cable or connecting powerful equipment to a weak line often results in melting the insulation, even if the contact itself is made qualitatively.
The main difficulty lies in the uneven distribution of current density and mechanical stress at the connection point. If you try to twist a 1.5 mm2 wire with a 4 mm2 cable, the thicker vein will act as a heat sink, but the transition site may not ensure that all fibers fit tightly, which will cause sparkling. Electric current is distributed evenly across the conductor only under ideal conditions, and any thinning or thickening along the path of energy creates a path of energy. transitional resistanceThis should be minimized by special adapters.
There are regulated ways of combining lines with different parameters that are allowed by the rules. PUE (Rules of Electrical Installation Devices). The use of specialized terminals, sleeves or solderings allows you to safely connect different diameters, maintaining the reliability of the entire power grid. However, simple mechanical twisting without additional protection elements is strictly prohibited, as this is a violation of basic principles. electrical safety.
Physics of the process: why does heating occur
When the flow of electric current through the conductor occurs heating, the intensity of which depends on the strength of the current and the resistance of the material. In the place where wires of different cross-sections are connected, the contact area is often smaller than the cross-section of a smaller vein, which leads to a local increase in the number of wires. current-density. This phenomenon is described by the Joule-Lentz law, according to which the amount of heat is proportional to the square of the current strength and the resistance of the chain section. If the resistance at the junction point is high due to poor contact, the energy starts to be released as heat, melting the insulation.
In addition, metals tend to expand when heated and shrink when cooled. Since copper veins of different diameters have different mass and thermal inertia, heating-cooling cycles cause microshifts at the joint site. Over time, this leads to weakening of the contact, increasing the gap and the appearance of sparkle. This is especially dangerous in hidden wiring, where access to the accident site is limited, and the burning of insulation can spread to building structures.
It is important to understand that transitional resistance It depends not only on the area of contact, but also on the quality of surface treatment. Copper oxides formed in air conduct current much worse than pure metal. In the connection of heterogeneous wire thicknesses, oxidation occurs faster due to the instability of the temperature regime. Therefore, any compounds must be sealed and protected from oxygen.
The dangers and risks of improper switching
Ignoring the rules of connecting wires with different sections carries a direct threat to property and people's lives. The most common consequence is overheating, which may not be accompanied by visible flames at the initial stage, but will lead to the destruction of the insulation layer. The result is a short circuit, which can trigger the circuit breaker or, in the worst case, a short circuit. fire.
⚠️ Attention: The use of twisting to connect wires of different diameters is prohibited by the rules PUE This is a gross violation of electrical safety standards.
Another hidden threat is the degradation of contact with time. Even if the connection initially seemed reliable, vibrations (especially in cars or industrial equipment) shake the twist. In the place of poor contact begins to release heat, which accelerates the oxidation of copper. This process is avalanche-like: more oxides - higher resistance - stronger heating. As a result, the wire can burn out at the joint, leaving part of the circuit without voltage or creating an arc discharge.
It is also worth considering the load on automatic switches. The machine is selected under the cross section of the weakest part of the chain. If you connect a thick wire with a thin one, but the machine is powerful (designed for a thick wire), then when overloaded, the thin section will burn up before the protection works. This creates a false sense of security when defense-automatic It's not doing its job.
Allowed methods of wire connection
For a safe association of lived of different diameters, there are time-tested and practice-tested methods. Each of them has its own application features and requires certain skills or tools. The choice of method depends on the operating conditions, availability of the connection site and the required reliability.
- 🔌 The terminal pads: the most versatile option, allowing you to reliably fix veins of different diameters without direct contact of metal with metal, using a screw press.
- 🔥 Pike: provides a monolithic connection and minimal transient resistance, but requires the ability to work with a soldering iron and fluxes, and is also impossible under voltage.
- 🛠️ Cartridge-pressing: The professional method, which provides high mechanical strength and tightness, is ideal for hidden wiring and automotive networks.
Clemmen like Wago or screw clips, allow connecting wires with a cross section from 1.5 to 4 mm2 or more. Inside such devices is often a contact paste that prevents oxidation. It is only important to choose the size of the terminal correctly for the maximum diameter of the wire to ensure sufficient pressure. Some models have a transparent body, which allows you to visually monitor the contact state.
Pike requires prior servicing of the veins. When connecting wires of different cross-sections, a thin vein can be wound onto a thick one and soldered, creating a reliable alloy. However, this method is time-consuming and not always applicable in cramped conditions. Pressure is performed by special mites and sleeves, which after deformation become a single whole with the wire. It's linkageNo maintenance required during operation.
Technology of pressing: step-by-step instructions
Pressing is considered one of the most reliable ways of connection, especially in conditions of vibration and high humidity. To perform the work you will need special shells (copper or tin) and press mites. The sleeve is selected so that the wires enter it tightly, but without excessive effort, which could deform the veins before the beginning of crimping.
The process begins with cleaning the insulation. The length of the section to be cleaned shall correspond to the length of the sleeve. Vests of different diameters are inserted into the sleeve from opposite sides to the junction in the middle. If the sections are very different, you can use a sleeve designed for a larger diameter, but then the free space is filled with scraps of copper wire for dense padding. This ensures uniform transmission of force during pressing.
The crimping itself is made at several points along the length of the sleeve. It is important not to overdo it and not to eat the sleeve with ticks, but also unsafe is also unacceptable. After mechanical fixation, the connection must be isolated. For this purpose, a shrink tube is used, which, when heated, tightly fits the connection, or a high-quality insulation tape. Thermosaur It is preferable because it provides better sealing.
Comparison of methods: characteristic table
To choose the best way for your situation, you need to compare the basic parameters of the available technologies. Below is a table showing the differences in reliability, complexity, and applicability of the methods.
| Method | Reliability | Difficulty | The necessary tool |
|---|---|---|---|
| Scooper | Low. | Minimum | Passenger |
| Clemmn | Medium/High | Low. | Screwdriver. |
| Pike. | Tall. | Tall. | The soldering iron, flux. |
| Pressure | Maximum | Medium | Press-ticks |
As you can see from the table, the twist loses in all respects except simplicity of execution, but this simplicity is illusory because of the risks. The terminals are a good compromise for household use, allowing you to quickly and reliably connect the lines. soldering and pressing require more time and skills, but guarantee a longevity of the connection for decades.
Pressing and soldering are the only methods recommended for hidden wiring and places with high vibration.
Frequent Mistakes and How to Avoid Them
Even knowing the theory, masters often make mistakes that negate all efforts. One of the most common is the use of aluminum and copper wires together without special adapters. A galvanic aluminum-copper pair in the presence of moisture creates a current that destroys contact. For such cases, there are bimetallic shells or terminals with quartz-vaseline lubrication.
⚠️ Attention: Never connect copper and aluminum wires directly, this will cause the contact to quickly break down and fire.
Another mistake is insufficient cleaning of the insulation or, conversely, too long cleaned part, which can stick out of the terminal and cause a short circuit. Also often forget about mechanical strength: the wire at the connection should not experience tension. If the cable is hanging on a twist or terminal, the contact will sooner or later be broken. Use clamps and fixtures to fasten the tourniquet.
Sometimes to increase the contact area in the twisting wires are preliminarily huddled. This is a valid method, but it turns a flexible wire into a rigid rod that breaks when bending. Therefore, tinted twisting cannot be used in moving elements or places subject to vibration. In such cases mechanical flexibility It is more important than chemical protection of the surface.
Technical nuances of servicing--
spoiler: When serving, use only acid-free fluxes (canifol) to avoid corrosion in the future. Acid residues destroy copper in a few months.
FAQ: Frequently Asked Questions
Can you connect wires of different cross-sections with a twist if they are made of the same metal?
Rules. PUE The twist is prohibited in any form, regardless of metal and cross section. The scroll can only be used as a preparatory stage before soldering or welding. Direct twisting of wires of different diameters does not provide a tight fit along the entire length, which leads to heating.
What is the maximum cross-sectional difference allowed in one terminal?
It depends on the specific model of the terminal. Usually manufacturers specify a range, for example, from 1.5 to 4 mm2. It is impossible to exceed the upper limit, since the screw will not create sufficient force. Connecting 1.5 mm2 and 10 mm2 in one small terminal will not physically work.
Do I need to sell the connection if a high-quality terminal is used?
No, modern spring or screw terminals do not require soldering. On the contrary, the soldered end of the wire in the screw terminal may eventually "flow" under the screw pressure, and the contact will weaken. A solid vein or a flexible multi-core wire with a tip is inserted into the terminal.
What to do if you need to connect a multi-core and single-wire wire?
It is best to use terminals with a clamping bar or shells. In screw terminals, the polycore wire must be necessarily terminated with a bushing tip so that the screw does not bite the thin veins and does not break contact.
Is it dangerous to roll on a short 1 cm section?
Yes, dangerous. The length of the site does not eliminate the risk of poor contact and oxidation. Even a short section of twisting of different diameters has a high transient resistance and can become a fireplace when the current load is exceeded.
For temporary connection in the field, use nut clamps or quick-clamp terminals, but replace them with a stationary solution at the earliest opportunity.