Test & Measurement

Tip of the Week: Using Your DMM to Safely Test for the Presence of Voltage

May 11, 2015

Follow these steps to avoid getting shocked.

Is it possible to use a DMM to verify that a circuit isn’t hot, and then get shocked anyhow? Yes, and you need to make that impossible. Here’s how you do it.

First, understand why the DMM might not read voltage that’s present. Several things can be wrong. For example:

• You have a broken test lead.
• The meter is selected for the wrong range.
• The meter is selected for the wrong function.
• The meter has been damaged and can’t read anything correctly.
• You think you’re measuring between hot and “ground,” but the point you’re touching with your black lead isn’t connected to anything (this sometimes happens with metallic raceway when the assumed “ground” isn’t there).

Except for that last problem, the following solution will work:

Test the meter against a known live circuit. If the reading is close to the expected (nominal) voltage, proceed to the next step.
Test the circuit for voltage. If you don’t read voltage, proceed to the next step.
Test the meter against a known live circuit, again. If it reads voltage correctly, you can be certain it correctly read the lack of voltage on the circuit you just tested.
Just to be double certain, repeat these steps again.

To avoid the “not connected” to ground problem, also measure between two phases or a phase and the neutral.

About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.