What is an effective grounding procedure to the electric shock prevention?

Earth of the appliance is very effective in the prevention of the electric shock . If the ground resistance is low, the effect doesn't limit any grounding procedure as the same. There are an effective grounding procedure and a grounding procedure with low effect.

Grounding procedure with small effect of electric shock prevention

The effect of the electric shock prevention : as a small earth example.

The high pressure of 6600V has been converted into 100V or 200V of the domestic use with the transformer on the utility pole in this figure. The second side of this transformer and the core of the transformer are grounded in the place in the utility pole (earth). Moreover, the leak breaker is assumed to be the one not used.

The voltage side of the power supply (hot side) is expediently assumed to be 100V to calculate potential, and the earth side of the power supply (cold side) is assumed to be 0V.

Then, the earth of the human body is shown to the independent one in this figure with the earth of the appliance. Therefore, the metal the exterior part of the appliance becomes 60V, and the voltage of 40V hangs to the human body though the potential of the human body when not getting an electric shock becomes 20V of the potential of the depth of the earth. And, it is not a current by dangerous in this case though flows to the human body the current of 4mA and gets an electric shock a little.

The voltage of 100V hangs in the human body if there is no earth in the appliance. Moreover, it is understood that the smaller the ground resistance of the appliance is, the lighter the level of the electric shock is when the earth of the appliance is away like this.

It is general that the leak breaker is set up recently. Because the power supply cuts by the leak of about 15-30mA even if the current leakage doesn't flow by as much as 400mA like this example, it is safe.

Grounding procedure with large effect of electric shock prevention

Next, the effect of the electric shock prevention : as an example of a large method.

The voltage side of the power supply (hot side) is expediently assumed to be 100V to calculate potential, and the earth side of the power supply (cold side) is assumed to be 0V.

Then, the ground resistance of the human body comes to have been connected with the earth point of the appliance (It is the same as the metal the exterior part) as shown in this figure. Therefore, the metal the exterior part becomes 60V, too and the current doesn't flow to the human body though the potential of the human body becomes 60V.

Even when the ground resistance of the appliance is larger than that of 100Ω, the electric shock can be prevented for this example.

When it is general, it is thought that it enters the state in the middle for the above-mentioned case and the postscript. Then, it is necessary to lower the ground resistance of the appliance as much as possible to prevent the electric shock generally.

Concrete grounding procedure that prevents electric shock

In conclusion, I think that a concrete grounding procedure that prevents the electric shock is good when as follows is done.

  1. The appliance individually does earth construction by the beeline.
  2. All those earths are connected by the ground lead in parallel and the ground resistance is lowered.
  3. They are evened up by setting up the earth in the four corners of the site, and in addition, the ground resistance falls further when everything runs parallel, and the potential of the earth in the site can be evened up. (Do not get an electric shock anywhere ..in the site... )

I am always doing the earth construction by a method near this. Individual earth construction can easily assume below 100Ω the ground resistance even if it is easy and can prevent the electric shock.