Insulation resistance should be at least one megaohm for every 1,000 volts of operating voltage, with a minimum of one megaohm.

Insulation resistance should be at least one megaohm for every 1,000 volts of operating voltage, with a minimum of one megaohm.

• A. One megaohm for each 1,000 volts of operating voltage, with a minimum of one megaohm
• B. Ten megaohms
• C. One ohm
• D. No minimum value

Answer: (A)

Insulation resistance is a safety check that shows how well the insulation prevents leakage as voltage increases. The practical rule is to have at least one megaohm for every 1,000 volts of operating voltage, with a floor of one megaohm. This scaling ensures the insulation can handle higher voltages without allowing dangerous current to flow through leakage paths. So, for a system at 1,000 V, you’d want about 1 MΩ or more; for 2,500 V, about 2.5 MΩ or more; and the minimum threshold never drops below 1 MΩ for low-voltage equipment. This criterion helps detect moisture, contamination, or insulation degradation because those issues lower resistance and increase leakage. The given answer matches this standard guideline. Other options don’t fit: ten megaohms would be appropriate only at much higher voltages (around 10,000 V), one ohm is far too low for insulation safety, and having no minimum value would ignore the safety margin needed at lower voltages.

Insulation resistance is a safety check that shows how well the insulation prevents leakage as voltage increases. The practical rule is to have at least one megaohm for every 1,000 volts of operating voltage, with a floor of one megaohm. This scaling ensures the insulation can handle higher voltages without allowing dangerous current to flow through leakage paths.

So, for a system at 1,000 V, you’d want about 1 MΩ or more; for 2,500 V, about 2.5 MΩ or more; and the minimum threshold never drops below 1 MΩ for low-voltage equipment. This criterion helps detect moisture, contamination, or insulation degradation because those issues lower resistance and increase leakage.

The given answer matches this standard guideline. Other options don’t fit: ten megaohms would be appropriate only at much higher voltages (around 10,000 V), one ohm is far too low for insulation safety, and having no minimum value would ignore the safety margin needed at lower voltages.