Unless your employer provides your test equipment, you’ve probably made a significant investment in at least one good digital multimeter (DMM). Maybe two. And you’d like to avoid that outlay again for a while. So would your employer, if your DMM is employer-provided. And if you’d like to improve your test equipment arsenal, replacing is going to deplete funds that could have been spent on acquiring more testing capability.
To avoid damaging a DMM, steer clear of these mistakes:
• Using the wrong jacks. At a nuclear power plant, an electrician turned his DMM into a molten mass. He accomplished this job-ending feat by measuring from a 480V bus to ground while having his test leads plugged into the current jacks. That 2A fuse isn’t designed to protect against this sort of abuse.
• Using the wrong setting. Most meters have some protection against this. For example, you have the DMM set on the 20VDC scale, but are measuring 120VAC. This typically will not harm the meter, you’ll just see “OL” on the screen. But try this stunt when the meter is providing power from its battery to the resistance terminals and you could seriously damage the meter.
• Storing it for “immediate access” rather than keeping it in a meter case. Most DMM cases have a pouch for the test leads, and you should use that. Wrapping the test leads around the meter and tossing it into a gang box (or shoving it into a tool pouch) is a sure way to degrade the integrity of those leads. If someone borrows your meter and returns it with the leads wrapped around it, replace the leads before using the meter.
• Using the wrong meter. If your meter is rated CATIII, don’t use it at the service switchgear. If it’s rated up to 1,000V, don’t even get it out around medium-voltage equipment.
• Using the current jacks. This isn’t in itself a problem, but if you’re in an industrial setting, it probably is. That’s because a typical DMM can measure small current values that are greatly exceeded by those you’d really care about in an industrial setting. Quick, how much current is that 100 HP motor drawing? Don’t use your DMM current jacks to try to read that. Instead, use a current clamp or other accessory. Typically, these will convert the current to a voltage you can read on the meter’s display as the amount of current. You can safely use the DMM’s current jacks, but be very aware of the application and environment before even considering doing so.