A electrical circuit is a simple or complex whole of conducting S and component S electric or electronic S traversed by a Electric current.

Electric laws

A certain number of laws applies to any electrical circuit. Namely:

  • Law of the nodes: the sum of the currents entering a node is equal to the sum of the currents leaving this node.
  • Law of the meshs: the algebraic sum of the electric potential differences is null.
  • Law of Ohm: the terminal voltage of a resistance is the product of the value of this resistance and the current crossing it.
  • the transformation delta-star.
  • the Theorem of Norton: any resistive circuit is equivalent to an ideal power source I , in parallel with a simple resistance R .

  • the Theorem of Thévenin: a linear electrical communication seen of two points is equivalent to a perfect generator whose tension is equal to the potential difference to vacuum between these two points, in series with a resistance equal to that which one measures between the points when the independent generators are made passive.

  • the Theorem of Millman: in an electrical communication of branches in parallel, including/understanding each one a perfect generator of tension in series with a linear element, the terminal voltage of the branches is equal to the sum of the electromotive forces respectively multiplied by the admittance of the branch, the whole divided by the sum of the admittances.

Circuits low tension

The circuits low tension (BT) relate to the Industrie and the building.

A circuit starts on the level of the table with a specific departure with a protection independent of the other circuits. Generally, each departure comprises only one cable, whose drivers have a section adapted to protection. Current standards (France, January 2006):

  1. Circuit breaker 10 amps = cable 1,5 mm ²
  2. Disjoncteur 16/20 has = cable 2,5 mm ²
  3. Disjoncteur 32 has = cable 6 mm ²
  4. Disjoncteur 40 has = cable 10 mm ², is used as general protection on the small installations (private individuals).

Circuits very low tension

The circuits Très low tension (TBT) relate to the Automobile and the Aéronautique.

The principle is of course the same one, except that only the driver Positif can be protected: the body is connected to the negative pole of the battery and is thus used as negative driver. The Disjoncteur S are replaced by fusible of small size, gathered very often under the instrument panel in a box with fuses , formerly located under the engine cowling. Moreover, the installation, being in TBT (tension < 50  V), does not need driver of safety (ground).

Electronics

  • Seuls the power circuits are generally protected, the others bringing into play low, even very weak currents.

  • In addition to the telegraphic circuits, electronics also knows:
    • Printed circuit: electrical circuits in copper tracks, on a plane support in Bakelite or resin epoxy, connecting the various components; the support is often called itself printed circuit , by Métonymie.
    • Integrated circuit: together of electronics components, fulfilling one or more functions, integrated in only one case simple to use.

Short-circuit

A short-circuit is a contact between two drivers. It involves the direct passage of the current “to shortest”, from one driver to another instead of crossing the remainder of the circuit. If it is involuntary, it is a defect which involves an increase in the intensity of the current and a potentially dangerous rise in the temperature of the drivers. To prevent that the current of short-circuit does not destroy the circuit of food, a protection is necessary: fusible Circuit breaker, , Limiting device of current. A short-circuit can cause a fire ! However it is important to generally know that the fires are often caused by bad contacts between drivers, a badly tight bridging-over terminal. Indeed a short-circuit causes a generally sufficient overcurrent to start the protection of the meter installed by EDF (principal circuit breaker). On the other hand a bad contact causes electric arcs and a heating likely to cause a fire. There is no currently protection against this kind of defect. It is thus necessary to take care of the quality of connections. Opinion with the handymen of Sunday…

See too

Related articles

External bonds

  • to solve a problem of short-circuit

Simple: Electrical circuit

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