Extech 380320 insulation measuring device 100 250 500 v cat iii 1000v extech 380320 p the extech 380320 analogue high voltage meg ohmmeter features three insulation test ranges with a live circuit indicator as well as low resistance and ac voltage measurements the power lock on feature allows hands free operation this manual ranging insulation tester is ideal for 250v 500v and 1000v test voltages this professional meter is shipped fully tested and calibrated and with proper use will