Measure Three-Phase Voltage

When taking voltage readings on a three phase piece of equipment, the voltage between each leg is measured and then averaged.  Here are the steps of this test:

• Set your True RMS electrical multi-meter to read “AC” or to the V with the wavy line. Select the approximate voltage you intend to test. If measuring HVAC equipment the approximate voltage can be found in the engineering data published by the manufacturer.
• Insert the black probe into the meter’s Common (COM) port and the red probe into the Test port (Normally to the right of the common port.)
• When testing assure your hands do not come in contact with the live electrical circuit or the metal end of the probe. Touch only the plastic or insulated handles of the probe.
• When you and others are all clear, energize the equipment.
• Place the black probe on an exposed ground wire or terminal.
• Place the red probe on the left hot leg (Phase One). Read and record voltage on phase one.
• While keeping the black probe on ground, place the red probe on the second hot leg. Read and record the voltage on phase two.
• Then with your black probe still on ground, place the red probe on the third hot leg. Read and record the voltage on the third phase.

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