TPI SDIT300 Digital Insulation Resistance Tester with AC Volts, 2000 Megaohms Resistance, 1000V, 600VAC Voltage Digital megohmmeter has three test voltages250, 500, and 1,000Vfor measuring insulation resistance to 2,000 megohms, and also measures low-resistance to 200 ohms Indicates with visual and audible warnings when a live circuit is detected Residual voltage is automatically discharged from the circuit under test when the test button is released Test button can be locked for extended measurement sessions. Model with AC voltage measurement is rated for CAT III installations to 600V, and model without AC voltage measurement is rated for CAT II installations to 1,000V