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Earthing purpose and points to be earthed

Short answer

Earthing connects system neutral or equipment frames to earth for safety, fault clearing and surge protection. Example: an earthed washing machine body allows a large fault current to trip the MCB, preventing shock. Points to earth include transformer neutral, motor and switchgear frames, metal conduits, cable armour, lightning arresters, portable appliances, structural steel and capacitor frames.

What is earthing? Explain its purpose with an example. Mention the points to be earthed in an industrial plant.

Earthing

Earthing is the connection of the neutral point of a supply system or the non-current-carrying metal parts of electrical equipment to the general mass of earth through a conductor of very low resistance, so that the earth connection is always at earth (zero) potential.

Purpose, with example

  1. Safety from shock: keeps exposed metal parts at earth potential.
  2. Fast fault clearing: gives a low-resistance path so the fuse/MCB trips.
  3. Stable system voltage: earthing the transformer neutral fixes the phase-to-earth voltage (230 V) and prevents it rising during faults.
  4. Lightning and surge protection: surge currents are discharged to earth.
  5. Discharge of static charge in places with fuel, dust or belts.

Example: a 230 V washing machine has its live wire touching the metal body because of worn insulation.

  • If the body is earthed (earth resistance about 1 Ω), a large fault current (about 230 A) flows to earth. The MCB/RCCB trips at once, and the body is dead before anyone touches it.
  • If the body is not earthed, the body stays at 230 V. A person touching it completes the circuit to earth through the body and gets a dangerous shock.

Points to be earthed in an industrial plant

  1. Neutral point of each supply transformer and generator (system earthing).
  2. Transformer tank, generator and motor frames.
  3. Metal enclosures of switchgear, panels, MCCs, distribution boards and bus ducts.
  4. Metal conduits, cable trays, trunking and the armour and sheath of cables.
  5. Lightning arresters and the lightning protection system (down conductors).
  6. Metal bodies of all portable and fixed appliances through the earth pin of sockets.
  7. Structural steel, cranes and crane rails, metal pipes and tanks (equipotential bonding).
  8. Capacitor bank frames and the secondary of CTs and PTs.
  9. Handles of operating mechanisms of switches and isolators.
  10. Fences and gates of outdoor substations, and stay wires of overhead lines.
  11. Equipment in hazardous areas (fuel storage, paint shops) to discharge static.

✓ Answer checked by Claude Opus 5.5 (high effort)

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