Protective Earthing
To prevent the destruction of people for short to ground, all the corps of receivers of electricity, all designs are made of metal, etc., which are a result of damage to the insulation may be under the influence dangerous voltage must have safety ground. Protective earth – this is just a ground, by executing it creates between the device (which is protected) and the ground is electric compound whose resistance is so small that if the closure happens to the body, the human touch to this body (parallel connection) will not be able to call through the human body such magnitude current, which could endanger his life or his health. It follows that for the current flow through the earth, you must have a closed circuit (sometimes imagine that the current "goes into the ground" – this is not true) and that for to secure suitable not any ground, but only the ground, which has a resistance, possibly small and in any case not above a certain value. If the safety ground is made in strict accordance with the requirements of emp, that is grounded satisfied with a sufficiently small resistance, then when you touch a grounded housing immediate danger does not arise. In some cases, despite the fact have completed the safety ground to ensure the security necessary to apply more additional steps (quick disconnect, equipotential bonding). Thus, in particularly adverse conditions (eg, damp places such as peat extraction, mining, etc.), as well as on those lines that feed the very expensive equipment, we have used a special high-speed protection that allows for the closure of the housing disable the alarm site. We have reviewed the above protective earthing and its purpose. In electrical installations have the grounding and other necessary operating conditions, such as grounding arrester, grounding the neutral of the transformer, etc. In contrast to the name of safety ground they are called the working ground.
