🔍 Key Concepts

• Insulation resistance testing with a megohmmeter (insul. res. tester) • Difference between low resistance (kΩ) and high resistance (MΩ) readings to ground • How the test leads are connected in figures 1 and 2 to specific phases (a, b, c) on Circuit #1 and Circuit #6

💭 Think About

• Look at figure 1 and trace exactly which phase on Circuit #1 is tied into the insulation resistance tester. Is that the phase giving the 8.3 kΩ reading? • Compare that with figure 2: which phase on Circuit #6 is connected to the tester giving 6.7 MΩ? What does that suggest about whether that phase is grounded or clear? • Ask yourself: on a healthy lighting circuit, would you expect a reading closer to a few kΩ or several MΩ? Which of these readings points to a ground fault?

✅ Before You Answer

• Verify which phase letter (a, b, or c) is being tested in each figure, based on the way the tester is drawn and connected to the bus and circuit arrows. • Confirm that 8.3 kΩ vs 6.7 MΩ represent very different conditions: one is essentially a fault path, the other good insulation. • Make sure the circuit breakers for #1 and #6 are open as shown, and think about whether any parallel paths could affect the readings, or if each measurement mainly reflects that circuit’s insulation condition.