Protective Earth

Protective Earth

Alternatives: Insulation or protective earth All components of a system or machine that can be applied with a dangerous voltage if a fault occurs must be taken into account. To guarantee safety, these components can either be double insulated or reinforced or they can be equipped with a protective earth.

Protective earth: Definition Protective earth is the earth that is mainly for guaranteeing the safety of human beings. The protective earth is a preventative measure for avoiding an electric shock caused by indirect contact, i.e., contact with a component that has been applied with a dangerous voltage as a result of a fault - failure in the basic insulation for example. NOTE: The protective earth is clearly separate from the functional earth. The functional earth is not for safety, it is a functional component; it is used as a reference voltage or for rerouting interference current for example.

Grounding arrangements and protective conductors The precision of the connection to the ground potential depends on the electrical equipment, the components and the type of current distribution (TT, TN, IT system). Some important standard principles for protective earth are:  The cross section of the protective ground wire must correspond with the maximum expected leakage current.  Electrical connections must correspond with the loads that are possible in practical operation.  The protective ground must also be guaranteed operational during service and maintenance work.  The protective earth overrides the functional earth. It may not e.g. be used to disabled to improve the electromagnetic compatibility. NOTE: IEC 60364-5-54 contains requirements for the earth system and protective grounding conductors.

Protective earth for PLCs Programmable Logic Controllers and their peripherals that belong to protective class I have a protective earth connection. There are two ways of connecting to the earth system:  The protective conductor is found in the power supply wire directly from the electric supply (mains).  The device has a protective conductor connection for connecting to an external protective conductor.

All components of the device that a person can come into contact with (e.g. frame, housing, mounts) are connected electrically and are connected with the protective conductor connection so that no dangerous voltage can enter. The protective conductor connection must remain intact when working on the device as long as the supply is connected. Requirements for the construction of PLCs and their peripherals can be found in IEC 61131-2 Programmable Controllers, Part 2: Equipment requirements and tests.