The 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