Most experts know that the requirements of electrical standards (PUE, in particular) for connection of conductors it is allowed to use welding, as well as crimping, soldering and special contact squeezes. It usually doesn't matter which of these connectors is used specifically. The main thing to pay attention to is that the contact area has very little resistance.
What it is?
To understand this issue, first of all, you need to find out what the transition resistance is and how it is formed in general. A contact joint is a special area between two tightly pressed electrically conductive materials. Due to the presence of microscopic irregularities on the surface of metals, electrical contact is formed not over the entire area, but only at a few points (photo below).
If you just press two bare conductors, the contact will turn out to be very unreliable, not providing the necessary conductivity in the contact zone. In this case, the resistance of the transition will be relatively large, which means one thing: it will lose or, more correctly, dissipate some part of the power transmitted through the circuit.
The specified indicator is called contact or contact resistance. For the normal functioning of electrical circuits, it should be as minimal as possible. The decisive factor that determines its value is the effort with which the connection is made.
Change over time
Even with the most reliable contact, the transition resistance in the working area will change over time, which is explained by the action of the following reasons:
- Influence of the environment (humidity and temperature).
- Features of the metal structure.
- Material temperature in the contact area.
note: At room temperature, about 20 grams. even stable copper oxidizes slightly over time.
As a result of this chemical process, an oxide film is formed on the surface of copper blanks, which significantly affects the quality of possible contact.
When the temperature in the contact area rises to 70 degrees (due to strong currents or poor connection quality), the rate of its formation increases sharply.
The situation is much worse in the case of incorrectly selected material. If you make contacts based on aluminum alloys, for example, the oxide film will appear even faster. Unlike copper, it will not be easy to destroy. If we take into account that the resistance of the oxide in this case is 10-12 Ohm / cm, it becomes clear that using this metal for electrical wiring is completely unacceptable.
In conclusion, we note that regardless of the method of connecting wires or cores in the working chain, the main attention is paid to the reliability of their contact. To assess its quality, you should use the developed and proven methods for determining the contact resistance.