Commonly asked questions regarding Voltmeters and Checking for Absence of Voltage.
What is the difference between measuring voltage and testing for absence of voltage?
Sometimes it is important to establish absence of voltage, and sometimes the intent is to determine the level of voltage. A worker needs to measure voltage to determine whether the voltage is 112 volts or 120 volts. When testing for absence of voltage, however, the only important issue is whether a voltage exists. Testing for absence of voltage is a go/no go or yes/no test.
How do I test for absence of voltage?
To ensure that both grounded and ungrounded circuits have no voltage available, a voltage test must include testing each phase conductor to every other phase conductor as well as testing each phase conductor to earth ground. The worker must ensure that the voltage rating is adequate for the circuit voltage. He or she must ensure that any adjustable controls on the meter are set to the appropriate scale also. The best practice for checking for absence of voltage is to use a single-function meter. If no adjustments are necessary and leads are hard-wired, the device cannot be set on the wrong scale.
Why is the voltmeter important?
Voltmeters are important because that are safety equipment. A voltmeter with an incorrect indication increases the risk of electrocution. If a voltmeter fails in service, an arcing fault can be the result. In fact, many injuries do occur because of voltmeter failures. Voltmeters are more important than some other safety devices because exposure to electrical injury exists in every instance. Therefore, you should keep voltmeters in a safe place and protect them from damage.
How do I choose a good voltmeter?
Voltmeters are designed and marketed for specific applications. Voltmeters purchased in electronics or home repair stores are likely to be designed for use in application in which available energy is low. Such devices should not be used on industrial equipment and circuits where significant amounts of energy are available. Workers should ensure that each voltmeter used has a third-party label, complies with consensus standards, and has a Category 4 static discharge rating.