Earthing Protection Systems Common Terms

Exposed Conductive Part

Any accessible metal parts of electrical equipment item other than the live part and which can accidentally become live.

Electrical Fault

Accidental connection between two points at different potentials, such as insulation fault.

Fault Voltage

Voltage, in case of an insulation fault, across an exposed conductive part and an earthing reference.

Direct Contact

Contact of persons with the normally live parts of electrical equipment

Non Direct Contact

Contact of persons with exposed conductive parts accidentally live due to an insulation fault.

Double Insulation

Insulation including both:

• Basic insulation required for protection against direct contact, and
• Supplementary insulation required for protection against indirect contact in case   of a fault of the basic insulation.

Discrimination

Coordination of the automatic switching devices such that only opening of the device cuts off the faulty part of the installation located immediately upstream of the fault.

Protective Conductor PE

Conductor used for protection against indirect contact and for interconnecting exposed conductive parts to one another; to extraneous conductive parts and to earthing electrodes or earthed parts.

Service Voltage

The rated operating voltage of a system, which together with the rated current of the system determines the load. For three-phase systems, it is the voltage between phases.

Residual Current

In case of an insulation fault, the residual current is the leakage current returned to the source through the earth and the protective conductor.

Residual Operating Current

Value of the residual current, which causes a residual current device to operate.

Shock Protection Device

This device must automatically separate from the source any part of the installation on which there is a fault hazardous to life. Depending on the system earthing arrangement of the installation, this device is either a residual current device, or an over-current device (fuse or circuit breaker)