Introduction
An earthing network carries leakage current and fault current from equipment, common mode current from external cables (electricity and telecoms mainly) and direct lightning currents into the earth.
Description
Physically, weak resistance (relative to a distant earth), does not concern us as much as the local equipotentiality of the building. In fact the most sensitive lines are those that connect equipments together. In order to restrict the circulation of common mode currents on cables which do not leave the building, it is necessary to restrict the voltage between interconnected equipments within the site.
A mechanical ground is any hardware conducting part which is exposed, which is not normally live, but which could be in case of a failure.
Follow all local and national safety codes and standards.
| DANGER | |
|---|---|
HAZARD OF ELECTRIC SHOCK If you cannot prove that the end of a shielded cable is
connected to the local ground, the cable must be considered as dangerous
and personal protective equipment (PPE) must be worn. Failure to follow these instructions will result in death or serious injury. | |
Principle
Basically nothing else has any effect on people's safety, in particular the earthing resistance or the method of connecting the mechanical grounds to the earth.
Equipments and electronic systems are interconnected. The best way to ensure that everything works properly is to maintain good equipotentiality between equipments. Besides the safety of the personnel, which is a LF (Low Frequency) constraint, equipotentiality between equipments must be satisfactory, especially for digital equipments even at very high frequencies.
Follow all local and national safety codes and standards.
| DANGER | |
|---|---|
HAZARD OF ELECTRIC SHOCK If you cannot prove that the end of a shielded cable is
connected to the local ground, the cable must be considered as dangerous
and personal protective equipment (PPE) must be worn. Failure to follow these instructions will result in death or serious injury. | |