- There are various formal definitions of a good Earthing, e.g., how many amp of current it can drain at a particular voltage, or resistance per surface meter.
- Good Earthing must have impedance low enough to ensure that sufficient current can flow through the safety device so that it disconnects the supply ( <0.4 sec ) and that voltage of earth doesn’t rise more than 50V.
In simple theory this will prevent a potential difference between earth and earthed parts, as well as permitting the flow of fault current which will cause the operation of the protective systems.
In an industrial plant or other facility that requires a grounding system, following factors influences requirement for a good grounding system.
- Limiting to definite values the voltage to earth of the entire electrical system. Use of a suitable grounding system can do this by maintaining some point in the circuit at earth potential. Such a grounding system provides these advantaged.
- Limits voltage to which the system-to-ground Insulation is subjected, thereby more definitely fixing the insulation rating.
- Limits system-to-ground or system-to-frame voltage to vales safe for personnel.
- Provides relatively stable system with a minimum of transient overvoltage.
- Permits any system fault to ground to be quickly isolated.