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Why was there a spark when I used a test probe?

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mistermac

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Since my oscilloscope ground probe was a small jaw type, it was inconvenient to measure screw terminals of a control board. I decided to attach it to a loose voltmeter probe that had a long metal tip for convenience sake. At first I decided to measure a terminal that had around 230 VAC voltage. At some point I may have detached the oscilloscope ground lead from my loose voltmeter probe, leaving it attached to the 230 VAC voltage. Eventually later I took out the voltmeter probe and then attached the oscilloscope ground lead to it. The moment I placed this on a screw terminal that was outputting 120 VAC voltage, there was a spark and the signals were lost from the board.
Does anyone know why the spark happened? Was it because there was still some high static voltage present on the loose voltmeter probe because I just left it at a 230 VAC terminal without attaching the other end to any device? I thought that even if the voltmeter probe still had some static voltage on it, the moment I attached the ground probe of the oscilloscope to it, any static voltage would dissipate into the ground line of the oscilloscope.
Can anyone help me out? Thank you very much!
 

Thunderchild

New Member
I think you accidently shorted something on your circuit, this is easily done when you are probing particarly when your using multiple leads, going from 230 V to 100 V would not be an issue on an osciloscope. be very careful when probing circuits
 
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