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When purchasing any electrical equipment - from the refrigerator to the washing machine, it is necessary to understand that it may one day not just break, and its emergency condition to endanger life person. To protect equipment against abnormal operation modes such as short circuit and overload, use protective devices and techniques.
First level "defense" human against electric shock due to abnormal operation of the electrical appliance is represented by a variety of devices, such as stoppers and machines. However, they are not always able to respond to disruption. Such cases is a disturbance or the appearance of the inner insulation voltage to the metallic device casing. To the person did not receive an electric shock when touching the equipment used special techniques reduce the voltage to safe values.
One such method is grounded. The compound metal live elements with electrical earth (ground loop), which normally not under voltage, but may be under him as a result of damage isolation. The slowdown is also required RCD devices.
Example: downlight without ground with damaged insulation is guaranteed to be energized. When trying to change a light bulb in a human electric shock device, with a high probability of discharge would be fatal.
Another method of protecting a vanishing - metallic compound of not live electrical parts with zero (zero conductor network). The function of this method performs the same as the ground - to protect humans, but doing it differently. So the network with the vanishing of electrical disconnection occurs, which has come under strain because of the insulation failure.
The choice of protection method depends on the electrical system. In installations up to 1000 V used five ground systems: TN-C, TN-S, TN-C-S, TT, IT. The vanishing also used in systems with EN, PE and N conductors in networks with solidly earthed neutral TN-C, TN-S and TN-C-S.
Continuing the theme 17 cribs on the arrangement of the stylish and comfortable home and not only.
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A source: https://novate.ru/blogs/080119/49044/