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Step by Step Guide to Earth Pit Resistance Measurement – SOP for Accurate Testing

Standard Operating Procedure (SOP) for Earth Pit Resistance Measurement

Fig - Earth Resistance Tester Wiring

Objective

To measure the earth pit resistance accurately using an Earth Resistance Tester.

Equipment Required

  • Earth Resistance Tester (with four terminals: P1, P2, C1, and C2)
  • Two terminal rods (for current and potential measurement)
  • Measuring tape
  • Hammer (for driving rods into the ground)

Procedure

Step 1: Preparation

  1. Clean the Earth Pit Properly – Remove any debris or obstruction around the earth pit to ensure proper connection.

  2. Check the Earth Resistance Tester – Ensure the tester is in good working condition.

    • The tester should have four terminals: P1, P2, C1, and C2.
    • Check if the pointer reads zero when the equipment is not in use.
    • If required, adjust the zero adjustment screw to set the pointer at zero.

Step 2: Connection Setup

  1. Short terminals P1 and C1 and connect them to the earth pit electrode whose resistance needs to be measured.

  2. Position the terminal rods:

    • Current Rod (C2): Place it 5 to 30 meters away from the earth pit and drive it 1 meter deep into the ground.
    • Potential Rod (P2): Place it 2 to 15 meters away from the earth pit, along the same axis as the current rod, and drive it 1 meter deep into the ground.

Step 3: Measurement Process

  1. Operate the Earth Resistance Tester:

    • Rotate the handle of the tester steadily until the pointer stabilizes without oscillations.

  2. Record the Earth Resistance Value:

    • Read the resistance value displayed on the tester.
    • Record the measurement in Ohms (Ω) for further analysis.

Precautions

  • Ensure firm connections at all terminals for accurate readings.
  • The rods should be placed in a straight line from the earth pit.
  • Avoid testing during wet or extreme weather conditions, as moisture affects the reading.
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