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DMM Mistakes Not to Make

DMM mistakes not to makeThe digital multimeter (DMM) is popular and useful. But mistakes with it can lead to poor test results or even disaster. Let’s examine a few of those.

  • Using the wrong CAT rating. If you’re working on 480V circuits, don’t use a CAT-I DMM designed for electronics. For services or feeders, use a CAT-IV DMM. The designation is on the instrument.
  • Using a “wiggie” instead of a DMM to test energization for lockout/tagout. One problem is the wiggie cannot positively verify that power isn’t present because the indicator is a light and not a voltage measurement. Another problem is its low CAT-rating range.
  • Using cheap knock-off DMMs. That $40 meter could cost you your life. The markings on it are almost certain to be false. You simply can’t build a safe industrial DMM for that price. One common problem is the posts are too close. Another is the case material isn’t sufficient for industrial use.
  • Hooking up the DMM before verifying the meter settings and correct test setup. That 2A meter fuse is not going to protect you or the meter from a connection error on a 2,000 480V bus.
  • Hooking up the DMM with a lead in each hand. One problem is you are exposing both hands to the energy source, and that means a current path across your heart. Another is you can set up an ionization path between the leads. Hook up one lead at a time, one-handed.

Source: Mark Lamendola | Mindconnection