If system voltage is 6 kV, the insulation resistance criterion IR > ?

If system voltage is 6 kV, the insulation resistance criterion IR > ?

• A. 6 Ω
• B. 6 MΩ
• C. 1 MΩ
• D. 60 MΩ

Answer: (B)

Insulation resistance shows how well the insulation blocks leakage current. For high-voltage equipment, a practical rule is to require about 1 megohm per kilovolt of system voltage, so the leakage stays at a safe, low level during testing. At 6 kV, that means a minimum insulation resistance of 6 megohms. With V = 6000 V and R = 6,000,000 ohms, the leakage current is I = V/R = 1 mA, which is a common target for insulation tests. If the resistance were only 1 megohm, leakage would be about 6 mA—too high; if it were 60 megohms, leakage would be about 0.1 mA—better than needed, but the criterion focuses on the minimum acceptable value. A value like 6 ohms would yield about 1 A leakage, which is unsafe. So the required criterion for a 6 kV system is 6 megohms.

Insulation resistance shows how well the insulation blocks leakage current. For high-voltage equipment, a practical rule is to require about 1 megohm per kilovolt of system voltage, so the leakage stays at a safe, low level during testing. At 6 kV, that means a minimum insulation resistance of 6 megohms. With V = 6000 V and R = 6,000,000 ohms, the leakage current is I = V/R = 1 mA, which is a common target for insulation tests. If the resistance were only 1 megohm, leakage would be about 6 mA—too high; if it were 60 megohms, leakage would be about 0.1 mA—better than needed, but the criterion focuses on the minimum acceptable value. A value like 6 ohms would yield about 1 A leakage, which is unsafe. So the required criterion for a 6 kV system is 6 megohms.