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I'm using a multimeter (Mastercraft 052-0052-2) and I decided to see if the frequency of an outlet would read 60hz. I switched my multimeter to the FREQ setting and plugged the RED test lead into the NEUTRAL of the outlet. Upon doing this, a loud bang occurred with a huge spark. Yet the outlet still works and the breaker did not trip. Could somebody explain to me what may of occurred?

The multimeter works fine and no fuses were blown. The BLACK test lead was just resting on the carpet floor. (It probably didn't touch the carpet though, since it the metal probe sits 2cm above the carpet.)

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    \$\begingroup\$ Did your meter come with a manual? Did you put your leads in the COM & F plug-ins on your meter? \$\endgroup\$ – Tim Spriggs Mar 28 '16 at 21:30
  • \$\begingroup\$ @Tim Spriggs Yes, here is one for reference. manualslib.com/manual/953499/Mastercraft-52-0052-2.html#manual \$\endgroup\$ – Markusmoo Mar 28 '16 at 21:40
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    \$\begingroup\$ Technically this CAT II rated meter isn't rated for direct outlet measurements (CAT III would be). \$\endgroup\$ – David Mar 28 '16 at 21:52
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    \$\begingroup\$ @Markusmoo see ni.com/white-paper/5019/en - CAT II is suitable for appliance measurements (which will usually be separately fused and unable to deliver the same current as a main circuit). CAT III is suitable for outlets. To take the extreme of this argument, why wouldn't your CAT II meter be suitable for the incoming supply from your utility company? That is (typically) the same voltage - but far more dangerous. Regardless this doesn't answer your question, just a curiosity. \$\endgroup\$ – David Mar 28 '16 at 22:00
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    \$\begingroup\$ @Markusmoo: It sounds to me as though you somehow shorted the live wire to ground by simultaneously making contact with the socket live terminal and either the faceplate or some internal earthed metal. \$\endgroup\$ – Transistor Mar 28 '16 at 23:31
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If you drew sparks with only a single probe, it suggests that you accidentally shorted across neutral to hot somewhere on the outlet.

Studying and understanding the manual and the limits of the meter would likely help you to avoid such mishaps. (Or even worse such as fire or electrocution.) Any kind of measurement of mains power should use considerable caution.

Unless the meter is rated for measuring mains frequency, it would be better to avoid measuring high voltages like that. For practical purposes, the frequency of the utility power is the least likely to change or be worthy of measurement. Unless you were getting power from a portable generator or some "off-grid" source.

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  • \$\begingroup\$ Possibly shorted the probe across a hot terminal and some other internal hardware at neutral or ground potential. \$\endgroup\$ – KalleMP Mar 29 '16 at 8:53

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