To Measure 12V to 220V AC and DC Voltage. To locate break point of an insulated wire. To check flow of current in an insulated wire from outside In phase line where board is open lamp hold will not work at 440 V bulb will be damaged where as 3 in 1 tester will indicate this different phase of 440 V by glowing more brightly If we get phase from one wire and at the other end bulb does not glow indicate wires are from same phase Fully insulated blade ensures shock proof working Easily attachable extension cord with a Test Probe. Easily checks, live, or Neutral wire, continuity or break in circuit.