DMM Lead Arc getting voltage from power strip - Page 1
Forum section: electronics / projects

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 08:10:23 pm
content: I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2020, 08:25:13 pm
content: It seems more likely that you had the meter on a (possibly mA) current range and the brief arc occurred before the meter fuse blew. What meter is it? Does it have separate terminals for the current ranges, or are the mA ranges shared with the voltage ranges (i.e. does it have 3 input jacks or 4)?It sounds as if you were lucky!

author: paul8f
author_rank: Regular Contributor
timestamp: July 25, 2020, 08:25:37 pm
content: Did you have the red banana plug connected to theAor10Aterminal of the DMM by mistake?If you did, the internal fuse will have done its job, and will be blown. On most DMMs, this will happen regardless of what function you had the dial set to.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 09:31:15 pm
content: Quote from: Gyro on July 25, 2020, 08:25:13 pmYou just put it on Volts or Amps, and then the SEL button functions as the DC /AC switch. You can also set the decimal readout with RAN button.The meter still works. It only has two inputs. Here's a picture and link:https://www.amazon.com/gp/product/B087JMPTRF/ref=ask_ql_qh_dp_hza

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 09:35:46 pm
content: Quote from: paul8f on July 25, 2020, 08:25:37 pmNo Amp plug. I could have had the dial on Amps, which could have created a short, so yeah, maybe. Would having the meter on DC while trying to measure AC do anything except produce an out of range OL reading?

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 09:36:33 pm
content: Quote from: Gyro on July 25, 2020, 08:25:13 pmThat only produces an OL reading.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2020, 09:41:04 pm
content: Hmmm. From the description it looks as if the current range is only on the clamp jaws (AC only).It looks as if you might either need to read them manual more carefully in case there are certain button selections that you need to make before measuring voltage, or the design has 'issues'.There's no way it should arc, even if the Cat II 600V/ Cat III 300V rating is fake!P.S. Actually, if there is no current range on the jacks and you have to push soft buttons to read voltage, then it has issues anyway!

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 09:50:52 pm
content: Quote from: Gyro on July 25, 2020, 09:41:04 pmThat's correct. The main function is of an AC current tool. It's the type you don't need to change Amp plugs. All the buttons do is change between DC and AC, just like a dial indicator would do.Set it to Current, and it measure AC current ONLY down to 1mA. I tested that last night using separate zip cord plugged into a lamp pulling 9 watts from the LED bulb. It did it!The RAN function just changed the decimals.SEL button changes between DC and AC voltage.SEL button changes between diode and continuity.That's it. very simple.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 09:55:55 pm
content: Quote from: paul8f on July 25, 2020, 08:25:37 pmThe fuse (if it has one) didn't blow. It still measure AC and DC voltage. I just checked the current function and it works too.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 25, 2020, 10:03:41 pm
content: Since you're all here, a couple of other things I was wondering about:1. When I use continuity and touch the leads together I still get .2. If I use my other leads, I get 000. Does this mean the leads are introducing resistance?I wanted to calibrate my soldering station or at least see if the temp is accurate, so I got this meter because it had a temperature and prob function.However, the prob is just a wire with a little bead on it.I think it would just melt if I tried to test my iron. So, I'm bummed about that. I should have paid closer attention to the description and pictures. I still need to review it. I've compared it with my other Amazon multimeter for voltage AC/DC and it's right in line, and the temp was compared to a calibrated food probe. The meter reads about 1.8-2 F higher. I've asked on Amaozn if the unit is fused or not.Other than that, the outside and function of the unit is solid. The dial is nice and positive, the unit is heavy, the clamp is strong, and the ABS is really thick on it.Other than the temp probe, I have no use for it really.

author: helius
author_rank: Super Contributor
timestamp: July 25, 2020, 10:24:17 pm
content: The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).Multimeter fuses are for protecting the current shunt, they do not do anything to the volt measurements and those still work after the fuse blows.If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 12:21:06 am
content: Quote from: helius on July 25, 2020, 10:24:17 pmGreat information. I appreciate you taking the time to share that information. It's very interesting to me. I see because the Clamp Meter is not a part of the circuit, so there is no danger of shorting it. Again, thanks a lot for that information. Read up a little on the K Thermo material, etc. Much thanks again.Is there anyway I can modify it to work as a temp probe for my soldering iron?

author: TheMG
author_rank: Frequent Contributor
timestamp: July 26, 2020, 01:07:41 am
content: Quote from: DW1961 on July 25, 2020, 08:10:23 pmThat multimeter does not have any current measuring function on the banana jacks. Thus, you should NEVER under any circumstance get any kind of arc from the leads, no matter which function you have selected! Any half decent DMM should be able to handle its full voltage rating on any voltage range, AC or DC, ohms, continuity, diode check, and any other mode it has, without any damage to the DMM itself or the leads.Basically this means your DMM is a piece of junk. It's either defective or poorly designed. You get what you pay for.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 02:08:00 am
content: Quote from: TheMG on July 26, 2020, 01:07:41 amI didn't pay for it. It was free. The product description says it will measure down to 1mA AC current. I put a 12W bulb in a fixture and used the clamp. My volts are right at 120V. It did it.It measured exactly .101 amp.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 04:52:09 am
content: Quote from: helius on July 25, 2020, 10:24:17 pmJust got this back from teh Amazon merchant:"I received this replay back fro the seller on Amazon, for what it's worth. He is saying it has both current and voltage fuses in it:"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."F-it! I can tear it apart and see if it really does?! It might be interesting. If it has fuses, I'm assuming it has a way to change them. I'll ask the merchant.

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2020, 05:07:37 am
content: Quote from: DW1961 on July 26, 2020, 04:52:09 amOh dear. A teardown should be interesting.

author: coppercone2
author_rank: Super Contributor
timestamp: July 26, 2020, 07:35:36 am
content: I have seen non obviously destructive sparks (high end meter must have had the protection circuit work) when contact was made with probes on the probe/board junction when using a DMM on voltages higher then its rating on the correct mode (i.e. 2kv). I think maybe it made LESSER sparks near the upper limit of its range.obviously a mistake (similar equipment but they raised the voltage level between models that had near identical circuit topology/components)

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2020, 11:48:16 am
content: Quote from: DW1961 on July 26, 2020, 04:52:09 amYep, they're talking complete bollocks.DMMs use VDRs and PTC thermistors for voltage ranges, and those only come into play when it is subjected togrossoverload.It will be using a current transformer for the current jaws (hence AC only), but it's easy to clamp the high impedance current output - actually a fuse opening on the output [Ed: of the] transformer would turn it into a very high internal voltage source!I'd return it as defective - only do a teardown if you don't have to break any seals and hide the serial number. Try to find one that isn't manufactured by "RockSeed"P.S. A reputable supplier would apologise for melting the end of your probe, scaring the life out of you, and ask you to return it for urgent investigation - not burble on about its mythical fuses.

author: tooki
author_rank: Super Contributor
timestamp: July 26, 2020, 12:37:08 pm
content: Quote from: DW1961 on July 25, 2020, 08:10:23 pmGiven 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).

author: helius
author_rank: Super Contributor
timestamp: July 26, 2020, 01:03:28 pm
content: Quote from: tooki on July 26, 2020, 12:37:08 pmThis is the most likely answerI've had this happen when probing the starter socket of a fluorescent desk lamp. Any time you measure terminals that are close together (and the wires in a power strip can be much closer than is evident from the outside) this can happen. It's good to learn how to use the probe tip insulators if you measure such things.

author: TheMG
author_rank: Frequent Contributor
timestamp: July 26, 2020, 04:53:43 pm
content: Quote from: tooki on July 26, 2020, 12:37:08 pmThat 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.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 07:08:53 pm
content: Quote from: tooki on July 26, 2020, 12:37:08 pmYou mean by pushing the leads into the power strip receptacle and shorting it on the ground in the receptacle?

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 07:15:09 pm
content: Quote from: TheMG on July 26, 2020, 04:53:43 pmThe 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.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 07:18:22 pm
content: Quote from: Gyro on July 26, 2020, 11:48:16 amIt was free.What do you think? Tear down? IF it doesn't have any fuses, then they need to be called on that.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 26, 2020, 07:59:54 pm
content: My guess is you had it in the ohms function. This will engage the PTC and low voltage clamp and I wouldn't be at all surprised if it caused a small spark. You would be looking at somewhere around a 3Kohm load across the line until the PTC heats up. The low voltage clamp is typically less than 20V and won't make much of a difference. It shouldn't damage the meter but I don't recommend playing with the line.In the voltage mode, I wouldn't expect the meter to start to have any effect until you reach what ever the MOVs start to conduct (assuming the meter even has them).

author: edpalmer42
author_rank: Super Contributor
timestamp: July 26, 2020, 08:08:42 pm
content: Quote from: DW1961 on July 26, 2020, 07:15:09 pmThat 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!

author: ozcar
author_rank: Frequent Contributor
timestamp: July 26, 2020, 08:43:16 pm
content: Quote from: edpalmer42 on July 26, 2020, 08:08:42 pmI’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.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 08:46:37 pm
content: Quote from: edpalmer42 on July 26, 2020, 08:08:42 pmExcuse 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.

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2020, 09:30:38 pm
content: Quote from: DW1961 on July 26, 2020, 08:46:37 pmWell it appears that I owe RockSeed an apology (well apart from the fuse [Edit:crapstuff] anyway).Time to get the cable cutters!

author: DW1961
author_rank: Frequent Contributor
timestamp: July 26, 2020, 09:36:27 pm
content: Quote from: Gyro on July 26, 2020, 09:30:38 pmYeah 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.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 27, 2020, 05:43:03 pm
content: Just got a reply back from RockSeed about replacing the fuses.:Q: Are the fuses replaceable?"Yes, just buy a universal voltage current fuse but pay attention to the size of the fuse"He also said make sure the dial is correct for volts amps and AC DC, and I suppose that is because somehow they are doing everything with two leads, instead of splitting it into an dedicated amp plug.

author: Gyro
author_rank: Super Contributor
timestamp: July 27, 2020, 05:51:59 pm
content: Well if thereareany fuses, then he should be advising HRC meter fuses, not 'just universal' ones. I'm still not clear if there are any current ranges on the probes, or just on the clamp. Only the instructions will tell you.I think you are duty bound to go searching for them now! [Edit: if he says they are replaceable, then they ought to be easy to locate]I think what he is doing is just giving generic multimeter feedback rather than anything specific to this particular product (still worrying advice on the arbitrary fuse choice though).

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2020, 08:44:02 pm
content: Quote from: DW1961 on July 26, 2020, 08:46:37 pmThanks for the update!It'd be interesting to see how the contacts are laid out internally. Clearly they're not designed to be probed, but then again, that's not actually a requirement for a receptacle. Given that it hasn't blown your home circuit breaker, I take it that no shorting occurs when only actual AC plugs are inserted?

author: ozcar
author_rank: Frequent Contributor
timestamp: July 27, 2020, 10:06:54 pm
content: Quote from: Gyro on July 27, 2020, 05:51:59 pmLooking at the picture of it, I don’t get any suggestion that it can measure current other than by the clamp.And, somebody specifically asked the Amazon seller “Can this measure current with leads also?” and was told, no, only via the clamp.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 27, 2020, 10:23:50 pm
content: Quote from: Gyro on July 27, 2020, 05:51:59 pmHe said there is no way to get current reading from the leads, only the clamp and only AC. I can ask which fuse?

author: DW1961
author_rank: Frequent Contributor
timestamp: July 27, 2020, 10:27:17 pm
content: Quote from: tooki on July 27, 2020, 08:44:02 pmNo shorting when a normal plug 'was' inserted. 'Was' because the strip itself is now pushing daisies in the world's ever-growing plastic pile, and the wire (pure copper too) has just added 10 feet of what looks like 12 AWG copper wire to my collection.

author: ozcar
author_rank: Frequent Contributor
timestamp: July 28, 2020, 07:07:05 am
content: Quote from: DW1961 on July 27, 2020, 10:23:50 pmI’ll bet there is no fuse.Your meter appears to be a re-badged BSIDE ACM81. That is the cheapest one of a trio of similar BSIDE meters, ACM81, ACM82, and ACM91. Comparison chart here:https://www.aliexpress.com/item/1970498378.htmlHere is a review of the posh model:https://lygte-info.dk/review/DMMBSide%20ACM91%20UK.html

author: DW1961
author_rank: Frequent Contributor
timestamp: July 28, 2020, 05:09:56 pm
content: Quote from: ozcar on July 28, 2020, 07:07:05 amOK I'm tearing it down! The review was for an older model, so I "hope" the dude wasn't outright lying to me. The one I have does now have a diode function too. Maybe they added a fuse? lol Thanks for that link. Now I know exactly how to disassemble it.Does this look like it has fuses? They wouldn't be under the board? Also, the reply about having fuses was by "Amazon Customer" but was worded "Our products have. . . ." When I clicked on "Amazon Customer" I got an Amazon 404 error. Something fishy going on here. I mailed the seller directly this time through the Amazon email system. We'll see what they say.

author: Gyro
author_rank: Super Contributor
timestamp: July 28, 2020, 06:26:10 pm
content: I see no fuses.The green blob is a PTC thermistor, to protect the Ohms, continuity, diode test etc. Q1, Q2, Q5 and Q6 are diode clamps (after the PTC).R7A and R7B are high voltage resistors, probably the top of the voltage divider for the volts ranges. Likewise R4A and R4B (probably lower voltage range).D1, D2, D3, and D6 will be the overload clamps for the output of the Jaw current transformer.I can't see any evidence of current ranges on the Jacks.Pretty much as expected, there's not a huge amount of protection on the Jacks for the Cat rating but pretty much as expected for the price range (try to avoid applying highish voltages when not on a volts range (it's always good practice to double check anyway).Fuses are only useful for direct (on the jacks) current ranges, so it really would have been surprising if you had found any. That's what you get from generic Amazon seller advice - I'm sure he meant well though, just lacking information / knowledge, don't hold it against him.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 28, 2020, 08:54:19 pm
content: Quote from: Gyro on July 28, 2020, 06:26:10 pmYou know I don;t know if it was the seller. It just said "Amazon Customer" but the answer started out "Our products. . . " So strange. I actually sent them an in Amazon email directly to the seller, so no way for them to avoid the question, fudge the answer.Is there anything can report from tearing it down that is either good or bad? I'll review it and add you analysis, if that's ok? Is it dangerous? Lacking in a way that is short lived? Anything you can think of.

author: wizard69
author_rank: Super Contributor
timestamp: July 29, 2020, 02:03:57 am
content: If the meter has a resistance capability I'd most certainly test the meter for proper operation on the resistance ranges. This highlights the value of having a set of precision resistors or at least resistors that you have measure to a high degree of precision, in your possession. They don't have to be of "calibration standard" quality but they should be well known as to their acutal values. The nice thing here is that there are all sort of examples right here in these forums of how to create quick check standards. I call them quick checks because the intention isn't to be good enough to calibrate in many cases but good enough to prove operation of the tool.If the meter still works I have a hard time believing that the meter caused your problem. It could be something you did or another factor.By the way while this might rub many the wrong way meter leads are expendable wear items in my mind. Be prepared to buy new ones any time the current ones are damaged, show contamination or have been stressed excessively. I work in automation, with high voltage AC and DC systems, and frankly this is an area where you get no second chances. I hate to even think about how much current could be discharged from some of the motor drive caps I have to deal with. These are likely small caps compared to some stuff people work on but they make me pucker every time I work on them.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 29, 2020, 07:59:38 am
content: Quote from: wizard69 on July 29, 2020, 02:03:57 amWizard. It was as bad power strip that allowed the leads to cross the neutral and positive.

author: Gyro
author_rank: Super Contributor
timestamp: July 29, 2020, 08:43:37 am
content: Quote from: DW1961 on July 28, 2020, 08:54:19 pmAs I mentioned, the level of protection is what you would expect in that price range. If it was a Fluke or something then you might expect VDRs, maybe even spark gaps - but that stuff comes with higher CAT ratings and you didn't pay for an expensive fluke, so you wouldn't expect them. At the same time, for general indoor mains use (wall sockets) and low voltages it should be fine (pushing the probes through mains strip internal metal parts permitting). Don't go probing around the inlet side of your breaker panel or substations and you ought to be fine. If you're going to do that, then buy a Fluke and some anti-flash gear.You can't pull it up for lack of fuses because you wouldn't expect fuses without current ranges on the jacks - and the fuse advice was from some anonymous Amazon user anyway, so far as you can prove.Check its voltage, resistance accuracy against another meter and if you're happy with it and its operation, then there's really nothing to fault for the price. I can't see anything obvious in the construction.

author: DW1961
author_rank: Frequent Contributor
timestamp: July 29, 2020, 05:10:28 pm
content: Quote from: Gyro on July 29, 2020, 08:43:37 amThanks. I gave it a good review and mentioned it's limitation, such as no DC current measurement.