Technical Papers: Distribution systems and protection against indirect contact and earth fault

The earth fault, caused by an insulation loss between a live conductor and an exposed conductive part, represents a plant engineering problem which may cause damage to the electrical installations and above all may jeopardize people; as a matter of fact, people could get in touch with an exposed-conductive-part not normally live but which, due to the fault, might have a dangerous potential to ground.

The scope of this technical paper is providing the reader with the necessary information about the main normative aspects regarding protection against earth fault and indirect contact, clarifying the relevant problems and illustrating the solution proposed by ABB SACE.

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This document is divided into three main parts:

• Normative      aspects        (definitions,  classification            of distribution systems, prescriptions regarding protection, etc.)

• ABB    SACE solutions        for       protection      against           earth   fault    and indirect contact

• Discrimination          of         the      protections    against           earth fault.

In addition, to complete this document, there are some annexes analyzing thoroughly further aspects of the protection against electric shock, in particular protection against indirect contact, combined protection against both direct and indirect contact, considerations on the neutral and protective conductor, etc.

The scope of this publication is providing the reader with the necessary information about the main normative aspects regarding protection against earth fault and indirect contact, clarifying the relevant problems and illustrating the solution proposed by ABB SACE. Particular attention is paid to the protection devices and to the way they operate (from the residual current devices to the last generation electronic trip units) and how to obtain selective co-ordination is thoroughly described.