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I was trying to measure the voltage across two connectors that connect to a 3-pin, 13 A plug as part of troubleshooting, to verify I had circa 230 VAC present.

However, when I connected my multimeter to each terminal, it sparked and actually tripped my main electrical feed. It also melted some of the plastic around the connectors.

The plug socket is able to power my laptop and a fan (two devices I just had to hand to test the socket).

The two connectors definitely did not touch one another and were separated by quite some distance. I had them removed from the device I was trying to power and they were just floating in the air connected to my multimeter probes.

I can't figure out what or how this happened, and why other loads such as my laptop charger work just fine. The multimeter is rated for 600 VAC and was not put into any other mode. It's fine and suffered no damage.

Any help would be greatly appreciated as I can't move on without solving this. I went through a different plug and fuse now and the same thing happened.

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    \$\begingroup\$ Did you have it set for voltage or current? \$\endgroup\$
    – JRE
    Commented Sep 28, 2022 at 16:50
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    \$\begingroup\$ Do you have a history of knowing how to use a multimeter? For example, measuring current vs voltage? \$\endgroup\$
    – DKNguyen
    Commented Sep 28, 2022 at 16:50
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    \$\begingroup\$ Post a photo of your setup. \$\endgroup\$
    – Justme
    Commented Sep 28, 2022 at 16:51
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    \$\begingroup\$ It's easy to believe the probes didn't touch and that the meter is set to an appropriate range, but is it possible you made a mistake? It certainly sounds like it was set to read current or you shorted it by accient without noticing. \$\endgroup\$
    – jonathanjo
    Commented Sep 28, 2022 at 16:51
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    \$\begingroup\$ Does the meter have two sockets for the probes? Or more? My favorite meter has a common and then one for voltage, one for low current and one for 10A... \$\endgroup\$
    – Solar Mike
    Commented Sep 28, 2022 at 17:28

2 Answers 2

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Most multimeters have 3 sockets to connect the probes:

  • One is negative for all measurements.
  • One is positive for all measurements except 10A current.
  • One is positive for 10A current measurement only.

If you plug the positive probe into the 10A current socket, it's wired for a current measurement (no matter what the dial is set to!) and this causes the described symptoms.

The reason there's a special socket for 10A current is so that the high current can bypass most of the internals of the multimeter, which have too much resistance for this type of measurement.

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Q: it possible you made a mistake? It certainly sounds like it was set to read current or you shorted it by accient without noticing.
A: Set for Voltage, AC and the range setting was 600VAC. definitely not. I checked twice each time and followed the flow of each cable. The multimeter was definitely set to measure voltage.

If that's the case, you have a defective meter, seemingly a dangerous one.

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  • \$\begingroup\$ Would be a real shame as I just bought it this morning... I was using crimp connectors and the cables were well separated so I can see why a faulty meter might be to blame \$\endgroup\$
    – Brandon Kellett
    Commented Sep 28, 2022 at 17:11
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    \$\begingroup\$ Try measuring a (small) battery on DC, try measuring a resistance. Be careful! \$\endgroup\$
    – jonathanjo
    Commented Sep 28, 2022 at 17:15

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