DISPELLING MYTHS & ENSURING A RELIABLE LV GROUNDING SYSTEM
When it comes to electrical safety, earthing is always the first line of defense. The Earthing system must be constructed in such a way that it is not required to be maintained.
Though the methodology of Earthing has been well defined for MV and HV systems, there are a lot of misconceptions and myths about the practices adopted in the LV grounding systems. The design resistance value of the LV earth system is important because the relay settings and coordination are finalized based on the fault currents which depend on the earth resistance value.
In India, the concept of maintenance free Earthing is gaining popularity while at the same time the Maintenance free concept is being more misunderstood.
Below are facts Dispelling Myths & Ensuring a Reliable LV Grounding System:
- MYTH: Use of Copper Electrode helps to obtain a low resistance.
FACT: The type of Metal used has no significance on the earth electrode resistance. None of the formulae given in any of the international standards factors in the type of metal in a calculation of the earth resistance. However, in highly corrosive areas, Cu or Cu coated electrodes are recommended due to better corrosion resistance. - MYTH: Low resistance can be obtained by using a special electrode.
FACT: As per IEEE80, IS3043 and BS7430, the resistance can be lowered only by altering the medium adjacent to the electrode — which is the backfill material — and not the electrode itself. - MYTH: Resistance to Earth Electrode with or without highly conductive backfill will remain the same.
FACT: In fact, there is an improvement of over 31% in value of resistance by using carbon-based backfill. - MYTH: The instrumental/electronic earth in a facility shall be maintained separately than electrical earth.
FACT: As per IEEE 142 & IEC 61000, if the electronic and electrical equipment earthing are maintained separately, dangerous overvoltage may be induced in the system during lightning/severe fault conditions, causing catastrophic failure of electronic equipment. - MYTH: Neutral of the source transformer and the Lightning Protection Earth must not be connected to the general Earth Grid.
FACT: BS7430, IEC 61000, IEEE 80 & IEEE 1100 recommend interconnection of Lightning Protection System earthing with the general earthing grid. Also IS3043 vide clause 22.1.3 & 22.3.1 recommends the adoption of Protective Multiple Earthing System for all installations with a dedicated source transformer.
Please let us know if you need further assistance or have any requirements: [email protected]
