Purpose, importance, and methods of earthing systems

Purpose, importance, and methods of earthing systems

1. What Earthing Is

Earthing (grounding) = connecting exposed metal parts of electrical equipment/system to earth (ground) via low-resistance conductor (earth electrode buried in ground), so that earth is at zero potential reference and fault current has path to ground.

2. Purpose and Importance (exam 5 points)

Purpose	Why Important
1. Safety of persons (shock protection)	If fault (live touches metal body), body becomes live at supply voltage ⇒ without earthing, touching body ⇒ current through person to ground (shock, fatal). With earthing, body is tied to earth (0V), fault current flows via earth wire (low $R$), blowing fuse/MCB quickly, and touch voltage remains near 0 (≈$I_{fault}·R_{earth}$ small)
2. Protection of equipment	Provides low $R$ fault path ⇒ high fault current ⇒ protection operates fast vs floating body that may stay live and damage
3. Voltage stabilization / reference	Ground is 0V reference for system, limits overvoltage due to lightning/static, noise reduction
4. Lightning protection	Lightning rod via earthing carries strike to ground
5. System earthing (neutral)	Neutral of supply transformer earthed ⇒ phase voltages remain stable, fault detection possible

Without earthing, faulted metal body could remain at 230V, undetected, lethal.

3. Methods / Types of Earthing Systems (exam list — 4 methods + system types)

A. Methods (electrode types):

Method	Construction	$R_{earth}$	Use
Pipe earthing	Galvanized iron pipe (40 mm dia, 2.5 m long) vertical in ground, surrounded by alternating layers of salt and charcoal (reduce $R$, retain moisture), top with funnel for watering	~5Ω (good)	Most common for buildings (excellent, long life)
Plate earthing	Copper plate (60cm×60cm×3mm) or GI plate (60cm×60cm×6mm) buried vertical at 3m depth, with salt/charcoal	~5–10Ω	Substations, larger
Rod earthing	Copper-clad steel rod (12–20 mm dia, 2–3 m) driven into ground (like pipe but rod)	~10–20Ω	Small, temporary
Strip/wire earthing	Copper strip buried horizontally at 0.5m depth in trench	Higher	Rocky soil where vertical not possible

Ideal $R_{earth}$: <5Ω for good earthing (IS:3043), <1Ω for power stations.

B. System types (earthing systems, IEC):

• TT: Transformer neutral earthed, equipment earthed separately (own electrode) — home (India TT).
• TN-S/TN-C-S: Neutral and earth combined in supply (PEN), equipment earthed to supply earth — UK.
• IT: Isolated or high-R neutral — hospitals, critical.

4. Worked Checks

Need to test earthing: use earth tester (fall-of-potential method), measure <5Ω.

Fault: live touches 10Ω body, supply 230V, earth wire 1Ω, body Rs? Without earthing, body at 230V. With earthing 5Ω, fault current=230/(5+1)=38A ⇒ fuse 16A blows quickly, touch voltage=38·5? Actually body to earth voltage= I·R_earth=38·1? Wait earth wire? Touch voltage ≈ I·R_earth =38·1? Actually depends. With good earth, voltage low.

Salt/charcoal: salt lowers resistivity, charcoal retains moisture ⇒ low R even in summer.

5. Exam Points

• Define earthing as connecting metal parts to earth via low $R$ — 3-5 marks, frequent.
• List purposes (shock safety, equipment protection, voltage reference, lightning) — 5-7 marks, very frequent (the most common earthing importance question).
• Describe pipe and plate earthing with diagram (pipe with salt/charcoal, plate size) — 7 marks, very frequent (almost certain to ask one method).
• State $R_{earth}<5Ω$ and TT vs TN — 3-5 marks, frequent.