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The Trainer #47: What measuring voltage on the ground side means

Making sense of what your Digital Voltmeter is trying to tell you
Sunday, November 1, 2015 - 08:00
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“Hey Pete! I checked the power and ground to the (insert any electrical component name here) but it still isn’t working.”

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“How did you check the power and ground?” I ask.

“I unplugged the connector and got 12.5 volts on the power side, then used my ohmmeter to check for resistance to ground on the ground side.”

When I worked fulltime in the shop, I can’t begin to count the number of times I went through this scenario. Trying to test the integrity of an electrical circuit statically and/or with an ohmmeter may have worked once upon a time, but that time passed about the same time I started in this business – and that was a long time ago.

I’ll also be among the first to admit that I struggled with electrical troubleshooting for many of those years. Heck, I still have to stop and think a minute about the meter reading I’m getting to fully understand what it’s trying to tell me. Becoming confident in your ability to handle electrical concerns is one of those “light bulb on” moments. You study and practice, watch and learn, ask questions and try again, until finally — you get it!

And once you do, you’ll realize that it is really rather simple to understand.

It begins with understanding some basic rules on how electrons act, what causes them to act the way they do, and a few basic testing methods that allow you to quickly see what rule is being broken. So come hang out with me in the November 2015 edition of The Trainer and let’s see if we can make today your “light bulb on” moment.

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