Test before touch

Abstract

Test before touch is a phrase that appears simple in concept but is deceptively complex. As with any voltage testing, proper PPE must be selected and worn. Test before touch requires training, planning, and knowledge of the equipment and in some situations special procedures. Three types of voltage tests are necessary for any low-voltage circuit: ground to phase, neutral to phase, and phase to phase. In addition, the minimum number of voltage tests must be considered. Typically, a high-impedance digital voltmeter is the first choice for testing a low-voltage system. A low- impedance voltmeter along with a proximity tester may be needed to verify induced low voltages. Medium-voltage systems have stronger electric fields that allow the use of proximity test devices. Precautions must be taken against a false indication of no voltage by ensuring that the medium-voltage circuit or cable section under test is not shielded. Also, as with low-voltage systems, stray voltages can be induced into medium-voltage systems. Higher currents can be developed, and special procedures to ground and remove these currents are required. Finally, the seven principles of test before touch discussed previously should be applied always, regardless of the type of system under test. In conclusion, always remember the following instruction: test every circuit, every conductor, every time, before you touch. These ten words could save your life.