Earthing Protection systems 1: common terms used

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

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