Directly connecting the CIP cable to the machine is one of the most common mistakes in installing introductory boards, which is often ignored by home craftsmen. Self-supporting insulated wire has a multi-wire structure of the vein, woven from thin aluminum threads, which creates significant differences from the standard copper cable VVGng. When such a wire is tightened into the terminal of the automatic switch under the influence of the screw pressure, the thin veins are deformed, flattened and eventually lose elasticity.
As a result of this physical process, a microscopic gap is formed at the contact site, which leads to heating, oxidation of aluminum and, ultimately, to melting the machine body or even fire. aluminum It has the property of "flowing" under constant pressure, and without the use of special adapters, reliable contact is almost impossible to ensure. The critical point is that a visual inspection of the tightened terminal will not show the beginning of the process of degradation of the contact until the smoke goes.
Modern standards of electrical installation and requirements of PUE (Rules of Devices of Electrical Installations) clearly regulate the ways of connection of heterogeneous metals and wires of different design. For safe operation of electrical wiring, it is necessary to use special transition sleeves, tips or terminal pads that allow you to correctly switch from the SIP to the copper input or directly to the automatic machine. Ignoring these rules turns the introductory node into a potential emergency point.
Why you can’t just put the SIP directly into the machine
The main problem lies in the physical and mechanical properties of materials used in electrical engineering. aluminumThe sip is much softer than copper used in contact groups of machines. When you tighten the plug screw, the screw tip crashes into the soft metal, but due to the multiwire structure, the load is distributed unevenly. The outer veins may be squeezed and damaged, while the inner veins will not provide proper contact.
In addition, aluminum is subject to strong oxidation in air. If an oxide film is formed at the place of contact with the copper plate of the machine, the resistance of the site increases sharply. galvanic pair Copper aluminum in the presence of moisture (which can condense inside the shield) triggers electrochemical corrosion. This process destroys the contact from the inside, making the connection unreliable even with a strong initial puff.
⚠️ Attention: Direct contact of the aluminum vein with the copper clip of the machine without the use of quartz-vaseline paste or bimetallic adapters accelerates corrosion at times. This can lead to a burnout of the input within one season.
Another factor is thermal expansion. When the current passes, the conductor heats up and expands, and when cooling, it shrinks. Since the expansion coefficients of aluminum and copper (plastics of the machine case) differ, there is a constant micromotion of the vein in the clamping. Over time, this leads to a weakening of the contact, the appearance of sparkling and characteristic crack inside the shield.
What happens inside the terminal when heated?
During cyclic heating, aluminum expands more than copper. This creates the effect of a “pump” pushing the wire out from under the clamping plate. The resulting gap gets air, causing oxidation and resistance growth, which leads to even more heating - there is a vicious circle, ending in fire.
Use of transitional cartridges and tips
The most reliable and professional way to solve the problem is the use of transition sleeves of the type GPA (sleeves transition aluminum-copper) or aluminium-copper tips. These products are a tube, one part of which is made of aluminum (for pressing SIP), and the other of copper (for entering into the machine). The connection of metals inside the sleeve is made by friction welding, which excludes electrochemical corrosion.
The installation process requires the presence of a special tool - press ticks. Conventional passages or hammer will not be able to provide the necessary compression density, which is achieved only when using the correct size matrices. Pressure It should be carried out in several methods, starting from the center of the sleeve to the edges, to avoid deformation and ensure the monolithic connection.
☑️ Quality check of the pressing
After pressing, the copper tail of the sleeve or tip can be safely clamped into the terminal of the automatic switch. In this case, you are already working with a monolithic or high-quality copper wire that behaves predictably. For additional protection, open parts of aluminum (if they are left outside the sleeve) are recommended to be treated with conductive lubricant.
It is important to choose tips with a narrow shoulder blade if the machine has narrow terminals. Standard copper tips of the TM series may not fit into the seat of the modular machine, and they will have to be sawed, which violates the integrity of the coating. There are special series of tips designed specifically for connecting to automatic switches.
Use of terminal pads and tyres
An alternative to pressing is the use of special terminal adapters. In the electrical engineering market, products such as terminals are widely represented. ZAP (or their analogues from IEK, TDM), which have an aluminum part for SIP and copper for connecting to the machine. Inside such terminals often already contains a contact paste, protecting the compound from oxidation.
This method is less time consuming, as it does not require a hydraulic press, but it takes up more space in the shield. The plug must be fixed to the DIN-rail or on the mounting panel, which is not always convenient in compact boxes. However, for branches from the main SIP to several machines, this solution is optimal.
- 🔌 Allows you to make a branch without breaking the main highway of the SIP.
- 🛡️ Provides galvanic decoupling of copper and aluminum.
- 🔧 It does not require special tools for installation, a screwdriver is enough.
- 📏 It takes up additional space (2-4 modules) in the shield.
When using a bus connection (comb or homemade tire), you can connect several machines at once to enter the SIP through the transition pad. This ensures uniform load distribution and simplifies the maintenance of the shield. If necessary, the replacement of the machine will not have to touch the main input wire.
Use terminals with a transparent case or viewing windows to visually monitor whether the wire is inserted to the end. This will eliminate the situation when the insulation gets into the clamping mechanism.
Should I use NSHVI tips for SIP?
A frequent question is the possibility of using NSHVI (NSHVI2) tubular tips for multiwire SIP. Technically, if you insert an aluminum SIP into a copper tin tip and press it, you get a copper tail. However, there are a few nuances that make this method controversial.
First of all, galvanic aluminum and tin copper (tin/lead) inside the shell of the tip still remains. If moisture penetrates the inside of the clamp, corrosion will begin exactly where it is not visible. Secondly, the coefficient of thermal expansion of aluminum and copper differs, which, with cyclic loads, can lead to a weakening of the compression inside the sleeve of the NSHVI.
However, if the use of specialized GPA shells is not possible, this method is considered acceptable "for fishless", but with the mandatory conditions:
- ⚡ It is necessary to use quartz vaseline paste before pressing.
- 🔩 Only specialized matrices for aluminum are required.
- 🌡️ You can not use tips designed only for copper, without considering compatibility.
Professional electricians recommend avoiding such a “hybrid” solution in places of responsible input, such as a private house or cottage. It is better to spend on one high-quality transitional GPA sleeve than to risk a fire due to savings on consumables. The reliability of the input into the building is the basis of all electrical safety.
Table of compatibility of cross-sections and adapters
For the correct selection of components, you need to know the cross section of your SIP cable. The most common cables are 16, 25 and 35 mm2. Below is a table of correspondence between cross-sections and recommended types of transition elements.
| Section of the SIP (mm2) | Type of transition sleeve | Diameter of the matrix | Max. current (A) |
|---|---|---|---|
| 16 | GPA 16-10 or 16-6 | 8.0 mm | 80 |
| 25 | GPA 25-10 or 25-16 | 9.5 mm mm | 100 |
| 35 | GPA 35-16 or 35-25 | 11.0 mm | 140 |
| 50 | GPA 50-25 | 12.5 mm | 180 |
When choosing a sleeve, it is important to pay attention to the second digit in the marking, which indicates the cross-section of the copper part. It must correspond to or be less than the cross-section of the terminal of the machine, but the throughput of the sleeve should not be less than the calculated load current. Undersection The adapter is unacceptable, as it will become a weak link in the chain.
Typical errors in the installation of input
One of the most serious mistakes is to try to “improve” contact by folding the vein of the SIP in half before inserting into the machine. It's strictly forbidden. Such manipulation disrupts the calculated cross-section of the conductor at the clamp point and creates an unpredictable distribution of currents, which leads to local overheating.
It is also common to use steel washers or plates as gaskets between the SIP and the terminal. Steel rusts quickly, especially in conditions of temperature changes, and contact disappears. Metal gaskets must be compatible with the materials to be connected or be bimetallic.
⚠️ Warning: Never use a heavy-pressed SIP knife to clean up the squirts. Aluminum veins are easily broken, which reduces the cross-section of the conductor and creates a point of thermal breakdown under load. Use only strippers or a knife with a heel.
Another mistake is the lack of sufficient length of cleaning. If the insulation falls under the clamping bar of the machine, there will be no contact at all, or it will be extremely unstable. The length of the cleaned part must correspond exactly to the depth of the terminal pad or sleeve.
We should not forget about mechanical protection. The junction of the SIP and copper sledding (even through the sleeve) is experiencing mechanical stress. It is necessary to ensure the fixation of the cable so that the weight of the span is not transferred to the terminals of the machine. Use plastic screeds or clamps to attach to the shield body.
The main rule of installation: Aluminum does not tolerate direct contact with copper and mechanical loads. Always use transition elements and fix the cable, removing the voltage from the terminals of the machine.
Frequently Asked Questions (FAQ)
Can you get the end of the SIP tin and put it in the machine?
No, you can't do that. The solder (tin) under the pressure of the screw of the machine "float" (the phenomenon of fluidity), the contact will weaken in a short time. In addition, qualitatively to get a multiwire aluminum wire is extremely difficult because of the oxide film, requiring aggressive fluxes, the remains of which can cause corrosion.
What is the time of puffing for SIP in the machine?
For standard modular machines, the puffing moment is usually 2-3 Nm (indicated on the case or in the passport). However, if you use a transition sleeve, you need to tighten the copper end of the sleeve according to the rules for the copper wire of the corresponding cross section. The pulling of an aluminum vein even through the sleeve is dangerous.
Should I change the machine if it is already blackened from the SIP?
Yes, I will. If the body of the circuit breaker is blackened or melted, its internal structure is broken. Thermal and electromagnetic protection could shift their characteristics, and the machine will not work at the right time. Replacement of the automatic and transition elements is mandatory.
Will a conventional copper twist be suitable for a temporary connection?
Even for a temporary connection, a twist of copper and aluminum is unacceptable. The electrochemical reaction starts immediately. If you need a temporary solution, use at least a nut-type terminal pad or a screw clip with separate sockets for different metals.