When assembling or upgrading an electric shield, almost every home craftsman faces a classic dilemma: how to properly distribute the load if the number of circuit breakers is limited. Often there is a situation when it is necessary to power several consumers, and there are not enough free seats on the DIN-rail. At this point, it is tempting to twist two or three wires under one clamp, believing that copper is copper, and it will pass the current.
Electricity does not tolerate approximate solutions. Safety of operation The power grid depends on the quality of the contact connections. Trying to save space or time during the installation phase can lead to heating of contacts, melting of insulation and, in the worst case, to fire. It is important to clearly understand the physical processes occurring at the site of the connection of heterogeneous metals and wires of different cross-sections.
In this article we will discuss the technical nuances, refer to the rules. PUE We will see if there are exceptions to the rule. You will learn why equipment manufacturers are categorically against connecting several veins under one screw and what legal ways exist to solve the problem of shortage of seats in the shield.
Physics of the process: why two wires are a problem
The main problem of connecting two or more wires under one clamp of an automatic switch lies in the contact area. When you pinch a single wire, the pressure of the screw or spring is distributed evenly across the surface of the vein. If two separate veins fall under the terminal, a microscopic gap inevitably forms between them, even if the connection seems dense visually.
Over time, under the influence of cyclic (heating during operation and cooling down when idle), the metal expands and contracts. Conductors with different cross-sections or different rigidity behave differently. A thinner vein can be passed, and a thicker one can be unpressed. At the place of poor contact, a transient resistance occurs, which leads to local overheating.
⚠️ Warning: Heating at the contact point can reach critical temperatures sufficient to ignite the plastic body of the machine or insulate the wires, even if the machine itself does not work from overload.
In addition, copper veins have the property of “flowing” under constant pressure. If you twist together a rigid monolithic wire and a flexible polycolial, the latter will lose shape over time, the contact will weaken, and sparkling will begin. Copper oxidation At the heating point, it will only accelerate the degradation of the compound.
What do the rules of PUE and the guest say?
If you look at the regulatory documentation, the answer becomes unambiguous. Rules for the installation of electrical installations (PUEs) paragraph 3.1.19. states that the wires shall be inserted into the apparatus so that there is no mechanical stress on the contact clamps. Although there may not be a direct ban on the number of lives in one clamping in the old editions, modern requirements for the quality of installation are treated strictly.
Electrical equipment manufacturers, such as ABB, Legrand or IEKIn their instructions for use clearly state: each clip is designed to connect conductor. Violation of this rule automatically removes warranty obligations from the device.
It is believed that if the wires have the same cross-section and material, they can be combined. However, even in this case, the risk of weakening the contact remains high. Control authorities when accepting objects into operation often reject shields with violated installation rules, requiring alteration.
Nuances for professionals
In some industrial series of machines there are special adapters or double terminals certified by the manufacturer for connecting two tires or wires. However, in the household series (modular machines on the DIN-rail) such options are not provided.
Risks of connecting different sections and types of living
The most dangerous mistake is to try to connect wires of different sections under one screw. For example, when the input of the machine 16 Ampere trying to bring input 6 mm2 and withdrawal 2.5 mm2. In this case, the thin conductor simply won’t be clamped properly due to the geometry of the thick neighbor.
The situation is aggravated if the types of living are different. Single-wire connection (monolithic) and multiwire wires are not allowed without a special end. The soft veins of the multiwire wire under the screw pressure spread to the sides, the contact becomes unstable.
- 🔥 The risk of local overheating and melting of insulation at the twisting site.
- ⚡ The probability of arc discharge when the contact is weakened.
- 📉 Increased transient resistance leading to voltage losses.
If there is an urgent need to combine the lines, you should use special devices, which will be discussed below, and not rely on the "maybe". Electrical safety It should be priority number one.
Legal ways to connect multiple lines
What if the shield space is limited and the line is divided? There are several proven and safe methods. The most technically correct use switch-up or tires. They allow you to apply the phase to a group of automata without unnecessary connections in the terminals.
The second option is the use of special terminal pads or cross-module. In this case, the input wire is connected to the terminal, which has several outputs, and already from it go separate lines to consumers or machines. This ensures reliable contact and the ability to control each connection.
You can also use it. double-machine (if the network configuration allows) or replace several single-pole machines with one multi-pole with the necessary uncouple, although these are rather exceptional cases for specific tasks.
Instructions: how to properly connect the machine
The installation process must be carried out with a completely de-energized network. Before starting work, be sure to check the absence of voltage at the introductory terminals using an indicator screwdriver or multimeter.
☑️ Checking before connection
Clean the end of the wire so that the insulated part does not fall under the clamp, but the bare part does not stick far beyond the terminal. Put the wire in the nest to the point. Tighten the screw with the force recommended by the manufacturer (usually 2-3 Nm for home machines), using a dynamometer screwdriver for accuracy.
After tightening, slightly pull the wire to make sure the fixation is reliable. If a multi-core wire is used, be sure to use tips Nshwi. This will prevent the individual veins from being bitten by a screw and improve contact.
| Type of connection | Admissibility | Recommended application |
|---|---|---|
| One wire under the terminal | Permitted. | Standard installation of any line |
| Two wires of the same cross section | Not recommended | Only in extreme cases with control |
| Different cross-sectional wires | Forbidden. | Use transitional terminals |
| Monolith + Multi-core | Forbidden. | Only through the guild or the terminal |
Common mistakes in the installation of the shield
One of the common mistakes is to “save” the length of the wire. When the wire is pulled, a mechanical stress is created at the contact point. When heated or vibrating, this contact quickly weakens. Always leave a small margin of length for easy installation.
Another mistake is to use tape to fix wires inside the shield instead of proper cable management. Not only is it ugly, it's also fire-hazardous. Plastic insulation It may not withstand temperature effects in the enclosed space of the shield.
Use a special contact paste (quartz-vaseline) when combining aluminum with copper or to protect against oxidation in areas with high humidity, although this is rarely required in dry home shields.
Don't ignore the markings. In a few years, when something has to be repaired, the lack of signatures on the machines will turn a simple search for a malfunction into a long and dangerous process.
Outcome recommendations and conclusions
To sum up, the technical ability to shove two wires under one screw does not mean the safety of such a solution. Rules electrical It is based on analysis of thousands of emergency situations.
If you want to make sure your home is protected, use only a single-wire connection. For branching lines, use additional terminals, combs or increase the number of modular places in the shield. This is the case where greed or laziness can actually lead to a fire.
The golden rule of the electrician is: One clamp, one wire. No exceptions for domestic conditions.
⚠️ Note: Any work in the electrical panel is carried out only after the complete disconnection of the introductory switch. Life and health are more expensive than the time saved in the installation.
☑️ Final check of the shield
Can I connect two wires of different cross-sections under one machine?
Absolutely not. A smaller cross-section wire will not be clamped properly, leading to heat and fire. Use the intermediate terminal.
What if there is not enough space in the shield for new machines?
Don't twist the wires. It is better to replace existing machines with more compact (if possible) or, more correctly, replace the entire shield box with a more roomy one.
Do I need to use tips for a monolithic wire?
For a rigid monolithic wire, tips are not required and may even worsen contact. Tips. Nshwi It is only required for flexible multi-core wires.
How often do I need to tighten contacts in the machines?
It is recommended to carry out prophylactic stretching of contacts every 1-2 years, since copper has the property of “flowing” under load, especially in the first year of operation.