Electronics > Projects, Designs, and Technical Stuff
DMM Lead Arc getting voltage from power strip
edpalmer42:
--- Quote from: DW1961 on July 26, 2020, 07:15:09 pm ---
--- Quote from: TheMG on July 26, 2020, 04:53:43 pm ---
--- Quote from: tooki on July 26, 2020, 12:37:08 pm ---Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
--- End quote ---
That would be pretty difficult to do on a north american receptacle. The slots for live and neutral are very narrow, in fact the probes on most DMMs insert very snug into them, which doesn't allow for any side-to-side movement of the probes so there's no way you'd be able to short the probes to each other, at least not without bending them.
It is possible however on poorly made power strips if the probes are relatively long for the probe to poke past the back of the receptacle and through the insulation of a wire, or a grounded chassis, but this would be rather unusual as most DMM probes are not much longer than a standard plug end.
--- End quote ---
The lead tip is about 3/16th longer than the plug spade. I was having a hard time getting a reading in the power strip. I do remember that and it was not like doing it in a wall receptacle, so maybe I did ground it out. It's a very good explanation.
--- End quote ---
That happened to me many years ago with an old 3-way adapter. I pushed the DMM probe in and shorted to either the neutral or ground. Quite an impressive light show!
If your power bar is screwed together, pull it apart and inspect it. If not, unplug it (!!) and then see if you can get continuity to neutral or ground by probing into the hot lead with the smallest insulated wire you've got. If you do, that power bar is dangerous! Cut the cable off and throw it away!
ozcar:
--- Quote from: edpalmer42 on July 26, 2020, 08:08:42 pm ---
That happened to me many years ago with an old 3-way adapter. I pushed the DMM probe in and shorted to either the neutral or ground. Quite an impressive light show!
If your power bar is screwed together, pull it apart and inspect it. If not, unplug it (!!) and then see if you can get continuity to neutral or ground by probing into the hot lead with the smallest insulated wire you've got. If you do, that power bar is dangerous! Cut the cable off and throw it away!
--- End quote ---
I’ll admit to doing that once too, also on a triple adapter – so long ago that power strips/boards/bars had not been invented (at least, I had never seen such a thing). It only took one probe to do it.
Perhaps two “melt points” might be visible on the probe?
Or, as suggested, if the power strip can be opened up, see if there is any way that the probe could have come in contact with two of the conductors, and look for “melt points” there too.
DW1961:
--- Quote from: edpalmer42 on July 26, 2020, 08:08:42 pm ---
--- Quote from: DW1961 on July 26, 2020, 07:15:09 pm ---
--- Quote from: TheMG on July 26, 2020, 04:53:43 pm ---
--- Quote from: tooki on July 26, 2020, 12:37:08 pm ---Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
--- End quote ---
That would be pretty difficult to do on a north american receptacle. The slots for live and neutral are very narrow, in fact the probes on most DMMs insert very snug into them, which doesn't allow for any side-to-side movement of the probes so there's no way you'd be able to short the probes to each other, at least not without bending them.
It is possible however on poorly made power strips if the probes are relatively long for the probe to poke past the back of the receptacle and through the insulation of a wire, or a grounded chassis, but this would be rather unusual as most DMM probes are not much longer than a standard plug end.
--- End quote ---
The lead tip is about 3/16th longer than the plug spade. I was having a hard time getting a reading in the power strip. I do remember that and it was not like doing it in a wall receptacle, so maybe I did ground it out. It's a very good explanation.
--- End quote ---
That happened to me many years ago with an old 3-way adapter. I pushed the DMM probe in and shorted to either the neutral or ground. Quite an impressive light show!
If your power bar is screwed together, pull it apart and inspect it. If not, unplug it (!!) and then see if you can get continuity to neutral or ground by probing into the hot lead with the smallest insulated wire you've got. If you do, that power bar is dangerous! Cut the cable off and throw it away!
--- End quote ---
Excuse my language but FUCK ME. I got continuity. I'm sure that's what must have happened. I had to search a little, but I got it.
Gyro:
--- Quote from: DW1961 on July 26, 2020, 08:46:37 pm ---Excuse my language but FUCK ME. I got continuity. I'm sure that's what must have happened. I had to search a little, but I got it.
--- End quote ---
Well it appears that I owe RockSeed an apology (well apart from the fuse [Edit: crap stuff] anyway).
Time to get the cable cutters! :)
DW1961:
--- Quote from: Gyro on July 26, 2020, 09:30:38 pm ---
--- Quote from: DW1961 on July 26, 2020, 08:46:37 pm ---Excuse my language but FUCK ME. I got continuity. I'm sure that's what must have happened. I had to search a little, but I got it.
--- End quote ---
Well it appears that I owe RockSeed an apology (well apart from the fuse crap anyway).
Time to get the cable cutters! :)
--- End quote ---
Yeah I'm not such in a hurry to dismiss what the guy said about the fuses either. Remember we have a language gap too. I'll ask him for a schematic, if he has one. The unit seems to do exactly what they say and it doesn't in ANYWAY feel cheap, or light, or anything like that. The dial is positive and clicks firmly in place, the read out is clear, the backlight works well, and the measurements for voltage and current were right on according to my math calculations and comparing it to my other DMM. I know it can do all of those things and still be spooky, too. I'll see if there is a way to tear it down without destroying it. I asked if the fuses are replaceable.
I did see another DMM with only two leads and it said it could do everything with only two leads, no current lead. That is spooky, but I'd want to understand it before blowing it off.
Yeah that power strip. Man. "Get the cable cutters."
Done.
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