The question of the correct connection of a self-supporting insulated wire (SIP) to the input circuit breaker causes heated debate among both beginners and experienced electricians. Many people believe that since the SIP core is quite thick and rigid, it does not require additional processing before tightening into the terminal of the machine. However, such carelessness can lead to loose contact, heating and even fire at the connection point. Correct installation - This is the key to the longevity of the entire electrical network of your home.
In this article we will analyze in detail the physical properties of aluminum conductors, regulatory requirements and practical aspects of using tips. You'll find out why galvanic couple aluminum and copper require special attention, and what tools are needed to do the job well. Ignoring crimping technology often causes failure of expensive equipment.
There is a common misconception that the insertion machine is capable of reliably fixing a twisted core without additional elements. In practice, this leads to the fact that under the influence of cyclic loads (heating and cooling), the contact weakens. Aluminum has the property of fluidity, which, in direct contact with the copper jaws of the machine without an adapter, leads to a gradual deterioration in conductivity and local overheating.
Physics of the process: why aluminum requires a special approach
The main problem lies in the chemical and physical properties of aluminum from which the conductive cores of SIPs are made. Unlike copper, aluminum quickly oxidizes in air, forming a film with high resistance. If you do not ensure the tightness of the connection or do not use special lubricants, the contact will heat up. In addition, linear expansion coefficient for aluminum is significantly higher than for copper contacts of the machine.
When current passes, the wire heats up and expands, and when it cools, it contracts. This process, repeated daily, results in a phenomenon known as “metal fluidity.” The core gradually deforms under the pressure of the screw, the gap increases, and sparking begins. Usage transition terminals (adapter terminals) or lugs allow you to compensate for these expansions and create a stable connection.
⚠️ Attention: Direct contact between the aluminum core of the SIP and the copper busbar of the machine without the use of quartz-vaseline lubricant or bimetallic adapters accelerates the process of corrosion and destruction of the contact significantly.
It is also worth considering that stranded SIP conductors (although they are often single-wire for sections up to 50 mm², but there are also stranded ones) when directly clamped with a screw can be flattened unevenly. This reduces the effective contact area. Application crimping turns a bundle or rigid core into a monolithic element that cannot be damaged when tightened.
What happens inside the terminal when it heats up?
When heated, aluminum expands more than copper. If there is no elasticity reserve or adapter, a gap remains after cooling. Sparks jump through this gap, oxidation intensifies, resistance increases, and heating increases. A vicious circle leading to a fire.
Regulatory requirements and standards of PUE
Addressing Electrical Installation Rules (PUE), you can find clear instructions regarding the connection of aluminum wires. Clause 2.1.21 states that connection, branching and terminating of wires and cables must be carried out using crimping, welding, soldering or clamping (terminals) in accordance with current instructions. Direct tightening of a bare aluminum core into a machine terminal that is not specifically designed for aluminum is often interpreted as a violation of technology.
Manufacturers of electrical products such as ABB, IEK or Schneider Electric, in the passports of their products they often indicate the type of permitted conductors. Most modern modular machines have combined clamps (copper and tinned), but even they do not guarantee reliable contact with the SIP without a tip due to the shape of the core. GOST R 50571.5.52 also regulates the selection and installation of electrical wiring, emphasizing the importance of matching materials.
If you ignore the requirements of the standards, you risk not only the security, but also the legitimacy of the connection. When accepting the metering unit, energy supply organizations may require alteration of the switchboard if they see irregularities in the installation of the input cable. Use of certified tips resolves all questions from the inspection authorities.
- 🔌 PUE 2.1.21 requires the use of special termination methods for aluminum conductors.
- ⚡ GOST regulates the types of connections and prohibits twisting and straight clamping without preparation.
- 🛡️ Safety precautions dictates the need to eliminate sparking in input devices.
Choice of tips: pin or ring?
To connect SIP to a circuit breaker, the most suitable option is pin lugs (type NShp or imported analogues). They are a copper or bimetallic tube, one side of which has a flat shank, and the other has a sleeve for the wire. The copper shank fits perfectly into the terminal of the machine, providing maximum contact area.
Ring tips (NKI type) can also be used, but they are less convenient for modular automation, since they require unscrewing the screw and inserting it under the washer, which is not always structurally possible in the narrow body of the machine. Bimetallic tips (aluminum-copper) are an ideal, although more expensive, solution, since they completely eliminate electrochemical corrosion.
When choosing a size, it is important to focus not only on the cable cross-section, but also on the pitch of the machine terminal. A tip shank that is too wide may not fit into the socket or, worse, damage adjacent modules. Always check geometric dimensions before purchasing a batch of tips.
| Tip type | Material | Application | Features |
|---|---|---|---|
| NShp (pin) | Tinned copper | Entering the machine | Flat contact, ideal for clamping |
| NKI (Ring) | Tinned copper | Bolted connections | Requires unscrewing a screw |
| AM (Aluminum-copper) | Aluminum + Copper | Humid environment, SIP | Full protection against galvanization |
| Sleeve GML | Tinned copper | Splicing | Not suitable for direct input into the machine |
Tool for high-quality crimping
The quality of the connection directly depends on the tool. It is strictly forbidden to use pliers or a hammer to crimp lugs on SIPs. This method does not provide the required contact density and can damage the metal structure. The work requires specialized press jaws (crimpers) with corresponding matrices.
For one-time work, hand pliers of the PK-2 type or similar, having replaceable dies for different diameters, are suitable. If the volume of work is large, it is worth considering a hydraulic tool. The main requirement is that the matrix must match the type of tip (hexagonal or point crimping). Correct crimping is characterized by smooth edges and the absence of cracks in the metal.
☑️ Checking readiness for crimping
It is also important to prepare the wire itself. The insulation from SIP must be removed with a special knife so as not to damage the conductors. It is recommended to clean and treat the aluminum surface before inserting into the tip quartz-vaseline paste. This will prevent air from getting inside the case and stop oxidation.
Step-by-step instructions for connecting SIP
The process of entering SIP into the machine requires consistency and accuracy. First you need to measure the required length of the cable to the machine, leaving a small margin, but not allowing any extra “beard” in the shield. Then the insulation is removed. The removal length should correspond to the depth of the tip sleeve plus 1-2 mm.
Next, the tip is put on and crimping is performed. Usually one or two crimps are sufficient depending on the length of the sleeve. After this, the shank of the tip is inserted into the terminal of the machine. The screw is tightened to the torque recommended by the manufacturer (usually indicated on the case or in the documentation). Tightening torque critical: under-pressure will lead to heating, over-pressure will damage the threads or housing.
⚠️ Attention: Do not use electric screwdrivers at high speeds to tighten the machine terminals - it is easy to strip the threads or crack the plastic case. Use a torque screwdriver or hand tool sparingly.
Use heat shrink tubing with an adhesive layer at the junction of the SIP insulation and the ferrule. This will protect the transition area from moisture and dust, especially if the shield is located outdoors or in an unheated room.
After installation, be sure to carry out a visual inspection and, if possible, thermal imaging testing under load some time after switching on. This will allow you to identify hidden installation defects before an emergency occurs. Prevention is always cheaper than repairing a burnt panel.
Common mistakes and how to avoid them
One of the most common mistakes is the use of tinned copper tips without insulating the junction with aluminum in an aggressive environment. Although tinning protects the copper, the aluminum-copper interface inside the liner can corrode without paste. It is also often forgotten that SIPs cannot be bent at an angle less than 10 cable diameters - this can damage the insulation and break the tightness.
Another mistake is using lugs with a smaller cross-section than the cable “to fit.” This leads to overheating at the narrowest point of the circuit. Or vice versa, the use of a tip that is too large, which has to be forcibly pushed into the terminal, creating mechanical stress in the contact group of the machine. Compliance with sizes - the golden rule of an electrician.
- ❌ Ignoring pasta: leads to oxidation of the contact inside the sleeve.
- ❌ Core twisting: before inserting into the tip, the SIP cores cannot be twisted, they must lie parallel.
- ❌ Re-crimping: if the tip is crimped crookedly, it cannot be crimped again side by side - only replace it with a new one.
The main conclusion: It is necessary to crimp the SIP when inserting it into the machine. This ensures reliable contact, prevents oxidation and complies with the requirements of the PUE, guaranteeing the safety of your home.
FAQ: Frequently asked questions
Is it possible to connect a SIP directly to a machine without a tip if the core is wrapped?
Technically this is possible, and the contact can work for years, but this is a violation of the rules and a lottery. The aluminum will “float” and the contact will weaken. The risk of fire and failure of the machine is too great to save on the cost of tips.
Which tip is better: tinned copper or aluminum-copper?
For the inside of the shield, where it is dry, a high-quality tinned copper tip (NShp) is sufficient. Aluminum-copper (AM) is better if there is a risk of moisture or maximum reliability of the connection between two different metals is required, but it is more expensive and more difficult to install.
Is it necessary to lubricate the contact inside the machine?
There is no need to lubricate the machine terminal itself; the necessary coating is already there. Only the entry point of the aluminum core into the tip sleeve is lubricated before crimping in order to displace air.
What to do if the pin tip is loose in the terminal of the machine?
This means that the wrong tip size has been selected (the shank is too thin). The use of copper pads or solder is strictly prohibited. It is necessary to replace the tip with a suitable size.