Multimeter, Earthing, Megger, Motors fundamentals

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🔌 Fundamentals of Electrical Engineering – Key Industrial Practices

1. Checking Electricity Supply

  • Always use a digital multimeter to verify supply voltage in an industry.

  • A line tester (test pen) may fail over time, and it starts glowing even at 5 V leakage, which may mislead.

  • A multimeter ensures accurate and safe readings.





2. Insulation & Winding Resistance Testing

  • For motor winding resistance and insulation testing, use a Megger (insulation resistance tester).

  • A standard multimeter may not provide correct insulation values due to low test voltage.

  • Megger applies 500V–1000V DC to check insulation strength accurately.

3. Importance of Earthing Grid

  • In industries, multiple earth pits should be interconnected in a grid.

  • Since resistance in parallel decreases, the overall grid resistance is lower.

  • During an earth fault, fault current safely flows to ground through the grid.

4. Separate Grids for Electrical & Electronics

  • Create separate earthing systems for power equipment and sensitive electronic systems.

  • This avoids electromagnetic interference (EMI) and improves equipment safety.

5. Single vs Double Earthing

  • Three-phase systems require double earthing for safety and redundancy.

  • Single-phase systems generally need only single earthing.

6. Nature of Electricity

  • Electricity is not exactly “flow of electrons”; in AC systems, it is more about the oscillation/vibration of electrons around a mean position.

  • In DC, electrons move in a drift motion.

7. Reversing 3-Phase Motor Direction

  • To change the rotation direction of a 3-phase motor, simply interchange any two phases.

8. Role of Capacitor Banks

  • Capacitor banks supply reactive power (kVAR) to improve power factor.

  • They do not consume active (kW) power.

9. Capacitor Bank Rating

  • Rated in kVAR (kilo volt-ampere reactive).

  • Formula:

    Q(kVAR)=V×I×sin⁡ϕQ (kVAR) = V \times I \times \sin \phi

    where ϕ\phi is the phase angle.

10. Earth Resistance Measurement

  • Use an Earth Resistance Tester (Earth Pit Tester) to measure resistance of earth pits/grid.

  • Ensures proper earthing quality for safe fault current dissipation.


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