Ground (electricity)

The electric ground is a concept which represents the ground (the earthy mass, from where the name of " terre") while considering it conducting and, by convention, with the potential zero Volt.

The legal definition is: “conducting mass of the ground,” (to include/understand: ground) “whose electric potential in each point is regarded as equal to zero” (according to Légifrance, bonds at the foot of the page).

This definition rests on the assumption not really exact that the ground is perfectly conducting and that its potential is the same one in any point. What is contradicted in practice, for example the specific time of a shock of the lightning in a precise point. The potential of the ground is not homogeneous any more and locally not with the average potential of the sphere. It is thus about a convention , but, basically, there would be sorrow to obtain better " zero volt" and the ground is enough with the daily newspaper. Moreover, which imports for safety is not so much the potential in the absolute but the equipotential one.

In practice, no driver not being perfect, the potential of a zero conductor, generally named wire of ground , will be necessarily null. However, except problem of installation, this potential is always supposed enough weak not to be dangerous.

It is advisable to have only one electrode earth on the same site, all the ground connections must by concept being inter-connected to remain equipotential.

Let us note that the word " terre" in electricity a whole whole of things gathers (see the other directions of the term).

Utility of earthing

The put at the ground has two principal utilities:

Detection of defects of insulation

Indeed, if an electric cable stripped (in particular a phase) has suddenly touched the metal carcass of an apparatus and that somebody touches this carcass, this person is electrified. In many countries, the apparatuses comprising a metal carcass must be connected to the ground, to generate a current in the event of problem. That allows the release of the differential circuit breaker. Or, failing this and as a last resort, that cuts the circuit by a Fusible or a Disjoncteur because there is then a short-circuit between phase and ground. Attention, even when the neutral is connected to the ground by the electric supplier, it does not exempt a local wire of ground. If not the defect would not be detected any more by the differential circuit breaker.

It is thus well the association of a differential circuit breaker with an additional wire of earthing which is in charge of the safety of the people.

In order to be certain to have a null potential between two close metal parts, and thus not to electrocute themselves by touching the two objects (example, in a bathroom), it is obligatory (and advisable!) to connect between them the pipes, door frames and other structures conducting to guarantee this equipotentiality.

This short-circuit is radical to avoid any problem and it is advisable to do it “with shortest”. I.e. to do what is necessary so that this cable is shortest possible between two objects but also by repeating the operation in several points if the length of the objects is large. In addition, of course, one connects also these connections to the ground to so preserve the operation of the differential circuit breaker by chance a current had suddenly circulated in the metal parts (example: a defective water-heater).

Technology

Because of its specific role of safety, the socket-outlets always distinguish without possible confusion this particular driver on a specific pin. The manner of making depends on the type of electrical outlet.

For the same reason, this cable has a specific color: according to the countries (it is the case for the European Union) one can find it in jaune  et  vert            (most frequent), even in green or even without insulator (cablette). One found it sometimes in the past in gray (from now on prohibited).

Other directions of the term

Most of the time, by extension and abuse language, the term of " terre" also indicate:
  • the electrode earth i.e. the whole drivers buried and inter-connected between them and which are thus with the potential of the ground (electric ground);
  • a connector block of ground or bar of ground , in general a conducting plate dévissable which ensures connection between the earth electrode and the remainder of the installation.
  • a zero conductor wire of ground or which indicates the cable of protection in itself (connected to the ground connector block) and which traverses all the installation;
  • a stitches ground which one finds on the electrical outlets and which is of course connected to a wire of ground.

The wire of ground (green/yellow) names " driver of protection"

See too

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