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It's probably not new to you, but sometimes we want to analyze a powered circuit with a multimeter. I love to do that, but I'm a little worried that I might burn some components or the whole circuit.

Are there any best practices, do's and don't for using multimeters on circuits and components ?

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When set for voltage measurements a multimeter will normally have an impedance measured in megaohms. Although that impedance combined with capacitance may affect the operation of some circuits I can't think of many practical situations where damage is likely to occur. When set for current measurement it's a different story because the shunt resistor may effectively present a short-circuit.

By far the most likely cause of damage (which I've done myself on the odd occasion) are the probes slipping and shorting something out. Apart from being careful in general putting some heatshrink over most of the probe to leave only the tips exposed may help. Also consider getting a set of appropriate test clips for what you're working on so they are physically secure.

Also consider personal safety if you're working at high voltages and make sure any probes you use have an appropriate voltage rating and reduce the chance of your hands slipping onto dangerous voltages.

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    \$\begingroup\$ +1 for the most dangerous thing being a short circuit. Can't count the number of times I've accidentally put one probe a bit too close to both Vcc and Gnd! - it never stopped the circuit from working though \$\endgroup\$ – Matt Taylor Apr 22 '13 at 9:33
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    \$\begingroup\$ Also remember that the ohm meter & continuity test modes apply a voltage to the circuit under test, which may not always be appropriate. \$\endgroup\$ – Chris Stratton Apr 22 '13 at 13:15
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If you're not sure about what you're doing, then don't measure currents but only voltages. By measuring currents you might introduce a short-circuit. Measuring voltages should be fine (as long as you don't blow up your multimeter, so be careful with the voltage range).

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    \$\begingroup\$ I don't really think that someone who is using a multimeter for the first time is going to find voltages to even damage the multimeter, let alone blow it up. \$\endgroup\$ – Anonymous Penguin Jun 17 '13 at 21:10

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