Electrical protection assures:
• Protection of circuit elements against the thermal and mechanical stresses of short-circuit currents
• Protection of persons in the event of insulation failure
• Protection of appliances and apparatus being supplied (e.g. motors, etc.)
The aim is to avoid or to limit the destructive or dangerous consequences of excessive (short-circuit) currents, or those due to overloading and insulation failure, and to separate the defective circuit from the rest of the installation.
A distinction is made between the protection of:
• The elements of the installation or circuits (cables, wires, switchgear.
• Persons and animals
• Equipment and appliances supplied from the installation
The protection of circuits:
• Against overload; a condition of excessive current being drawn from a healthy (unfaulted) installation
• Against short-circuit currents due to complete failure of insulation between conductors of different phases or between a phase and neutral conductor or between a phase an PE or earth.