Voltmeters

One of the most common variables measured during stray voltage investigations is voltage. Generally this measurement is made using a voltmeter. The typical types of voltmeters include:

  • The Analog Volt-Ohm Meter (VOM),
  • The Digital Multimeter (DMM), or
  • The Oscilloscope.

A voltmeter must have a resolution of 0.1 V and an input impedance of at least 5,000 ohms per volt. It should also have the ability to monitor transients and to record voltages (or currents) over time, that is, to detect events that occur only at specific times and/or for short periods. Occasionally only a more sophisticated instrument, like a differential oscilloscope, can detect the exact waveform of voltages.

Since neutral-to-earth voltage is the most common source of stray voltage, it may be worth the effort and expense to install a voltmeter permanently. This voltmeter should monitor the voltage differential between the neutral bar of the service entrance panel and a reference electrode driven into the ground at least 30 feet from the building and away from any underground pipes or wires.