Why do my multimeter wires keep melting? - Page 1
Forum section: electronics / beginners

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 08:05:05 am
content: This has happened 3x now and have to patch them each time.I don't even see it happening each time so far. I only notice it another day when I come to take them out and notice no readout from the device then see one has come away again.They are only cheap and super thin wires but why are they burning out for what I thought was normal operation of voltage readings? What I have mostly been using them for is testing either the starter or leisure battery terminals, 72ah and 105ah, respectively, or the 60a dc-dc charger.I think it said 10a max current on the multimeter but does the current run through the wires exceeding that when placing them on the terminals of the batteries/charger just reading the voltage?I thought that the current going around the multimeter would be limited or is it not? No idea really.Please help explain so I might avoid.

author: IanB
author_rank: Super Contributor
timestamp: January 07, 2025, 08:26:44 am
content: It's hard to make any sense out of what you have written.The wires are melting, or they have "come away", or they are burning out, but you don't see it happen?If they are really melting or burning out, there would be a smell of burning, there would be heat, maybe smoke. You would definitely see it happening.But this isn't going to happen if you are measuring voltage. It might if you try to measure current, or put the leads in the wrong socket of the meter, but most meters have a fuse that would blow if you do that. Only the cheapest meters might have no fuse.Are you sure you are not stretching them or breaking them by pulling too hard or something? Or are you soldering and letting them touch the soldering iron?Nothing really makes any sense about any of this.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 08:31:53 am
content: Quote from: IanB on January 07, 2025, 08:26:44 amThere is no smoke or anything like that. They wires have detached from the plug or the pin end. I am not rough with them so I just presumed it was due to over voltage but maybe something else as you say.By coming away I mean like snapped, but I didn't snap them, not connected and the wire is broken which is happening at the base each time. It happened for both ends where the pointy things go that you use to make the readings and the third time it has happened at the other end where the plug is.Ok so to confirm this cannot happen for doing voltage checks. How come?Oh I forgot to mention I do continuity tests often too, could that cause it?

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 07, 2025, 08:36:08 am
content: - If you are measuring voltage, no current of meaningfull magnitude runs though the leads- If you are measuring current (knowingly or not, ie if you are using the current terminal) the inputs are fused (or should be fused, YMMV with the cheap crap out there) but that is the only "limit" imposed: the current will not automatically be limited to 10A or something like that but if you are exceeding 10A in a meaningfull way, the fuse will blow and open after which it needs to be replaced before you can measure current again.- If you have a cheap meter, even if the meter is capable of 10A the leads may start to give way well before 10A especially if you have been somewhat abusive to the leads in the past.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 08:41:51 am
content: Quote from: Ice-Tea on January 07, 2025, 08:36:08 amThanks, did you read my second reply above which gives more detail, as you may have posted before I posted it?I certainly haven't measured current except once or twice to try it, not with any regularity or around the times when these wires have come apart.Btw this is a new meter which I only got a couple of months ago so not like they would have just frayed and disintegrated from years of service. Maybe from being poor quality but I find even that hard to believe at least in terms of manual force breaking them since even the plastic insulation should protect them from being too flimsy. Melting on the other hand I have no idea, which is why I asked here.If the wires are only a couple of hairs in thickness there really be a noticeable smell and smoke? I am just trying to figure out how it happened or the likely cause.

author: IanB
author_rank: Super Contributor
timestamp: January 07, 2025, 08:51:45 am
content: Quote from: electroniclearner820327 on January 07, 2025, 08:31:53 amIt still doesn't really make much sense. If the probe leads break at the ends where they are attached, it suggests a mechanical cause like bending them too much. How exactly are you fixing them if they break? Normally, test leads breaking like this doesn't happen, and normally the fix is to buy new test leads.

author: SteveThackery
author_rank: Super Contributor
timestamp: January 07, 2025, 10:06:00 am
content: I think this can only be cheap and nasty leads. I'm sure the problem will go away if you buy some new leads.PS: I do wonder if these might be the notorious steel leads discussed elsewhere. Make sure the ones you buy are copper.

author: NE666
author_rank: Frequent Contributor
timestamp: January 07, 2025, 10:07:57 am
content: Quote from: IanB on January 07, 2025, 08:51:45 amSeconded. To me, it sounds as if the OP has some truly cheap, shitty test leads and they're not up to the job. Remedy is to shell out a few dollary-dos on some half decent ones and throw the damaged ones away. In my experience, pretty much anything from Amazon would be better than what they are describing. However, if you're making regular use of them, it's worth your time and money going with quality.

author: Ian.M
author_rank: Super Contributor
timestamp: January 07, 2025, 10:30:29 am
content: I've had pocket meters with captive leads that had no strain relief at the probes. This was before all the cheap stuff went to overmolded connector/probe bodies so the probe body was a plastic tube with a probe tip with a knurled solder-cup base pushed into it. They invariably broke where the wire entered the solder joint as there was nothing to stop any slight twisting movement fatiguing it. Eventually I wedged the wires with a sliver of match stick where they exited the probe body, and heatshrunk over them to add strain relief and for the rest of the life of the meter, I had no further problems.However SteveThackery and NE666 have the right of it - trying to fix test leads that even when brand new aren't fit for purpose is a waste of time and effort so get a decent set of budget test leads to replace them.Also, when you put a meter away DO NOT wrap the leads tightly round the meter body, or bend the lead sharply back on itself where it enters the probe body as this strains the leads where they enter the plugs and probes. Its better to bundle the leads and put a velcro cable tie or a rubber band round the bundle

author: shapirus
author_rank: Super Contributor
timestamp: January 07, 2025, 10:35:15 am
content: pictures?

author: Gyro
author_rank: Super Contributor
timestamp: January 07, 2025, 12:44:47 pm
content: It sounds to me as if you are trying to measure voltage with the leads still plugged into the 10A current jack. If the meter isn't fused, the excessive current could cause the leads to unsolder themselves and the hot insulation to allow the wires to pull out.What make and model of meter is it? We need to establish whether the 10A range is internally fused or not.

author: ArchieAltz
author_rank: Contributor
timestamp: January 07, 2025, 01:05:26 pm
content: Quote from: electroniclearner820327 on January 07, 2025, 08:05:05 amYou might've made a mistake I made once , if you ever measured current and connected in parallel instead of in series , you could have overheated the wires and they "melted". That's just my 2 cents idrk what happened since I couldn't understand it fully

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 01:23:05 pm
content: Quote from: Gyro on January 07, 2025, 12:44:47 pmI think it is this. Someone suggested similar on another forum and I looked and I had the negative lead in the 10A port and the live in the other one on the right but the COM (which I now realize must mean common negative) empty! Would that have done it? I looked in the manual again and sure enough of course it was wrong! They were still giving accurate readings so did not think anything amiss.Oh and it is unfused, up to 10a.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 01:25:56 pm
content: Quote from: NE666 on January 07, 2025, 10:07:57 amAs to how I am fixing them I would strip the wires to reveal the 2 or 3 hairs of wire they give, which do seem copper as they are brown and put heatshrink over the wire. So far no issues after doing this 3x but of course the ports were plugged wrong, as above so that is maybe the most likely factor?

author: Ian.M
author_rank: Super Contributor
timestamp: January 07, 2025, 01:38:44 pm
content: '10A' is internally connected to 'COM' via the current shunt for the 10A range, which is a fairly thick strip of metal or piece of wire. You *shouldn't* use it with the leads in '10A' and the volts/ohms jack, but it would read correctly except on low ohms ranges and wouldn't damage the meter or leads.If test leads have less than 7 strands they are absolute 💩 junk. Low quality leads (not suitable for regular use) may only have 7 strands. Medium quality leads will have >20 strands, and good quality leads >60 strands.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 07, 2025, 01:52:53 pm
content: I don't think it's burned out! I think it just breaks because the wire is too small so it breaks at the bend after a while.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 07, 2025, 02:57:54 pm
content: Quote from: Ian.M on January 07, 2025, 01:38:44 pmOk that is good to know it is par for the course rather than some reading I may have done which could have burned it as for the latter I was getting worried with each reading I made whether that would cause another burn out.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: January 08, 2025, 01:47:16 pm
content: This 'Mystery Meter' is obviously one that we should ALL avoid

author: CaptDon
author_rank: Super Contributor
timestamp: January 08, 2025, 02:05:01 pm
content: Having one side of the high current shunt connected to COM jack and the other side connected to the 10A jack and being unswitched is common. The switch if used would add an undetermined number of milliohms to the shunt based on condition and oxidation within the switch. Having one lead in the COM jack and one lead in the 10A jack and setting the meter to measure voltage and then trying to measure the voltage of a car battery would definitely melt a bunch of stuff. Also, the high current shunt may not be fused because the type of fuse and condition of the fuse holder will create large inaccuracies in the measurement. Cheap ass meters don't even include any switch capable of passing 10 amps,

author: SteveThackery
author_rank: Super Contributor
timestamp: January 08, 2025, 02:39:12 pm
content: I think we're off on a wild goose chase. The OP reports that the leads sometimes fail when they are in storage.We don't have any evidence to support the excessive current theory, and I'm pretty sure the OP would have noticed the sparks and smell. I still think the right approach is to buy some decent leads to start with.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: January 08, 2025, 03:01:43 pm
content: It may happen to to a wrong setting or a wrong placement of the probes. Without seeing how you are measuring, it is fifficult to say.

author: CaptDon
author_rank: Super Contributor
timestamp: January 09, 2025, 02:01:33 pm
content: The term melting implies severe overcurrent for a time period long enough to create the melt. However, in the O.P.'s later comments it seems he is indeed talking about the constant lead breakage causing the open circuit condition and that speaks of very poor quality test leads which sadly are getting more and more common. I was very lucky that someone in the company prior to me hiring on ordered 100 foot spools of very high quality Belden or Alpha multi-strand tinned copper with real rubber insulation 'test lead' wire in red, black, white and green. It is even marked 'Test Lead Wire' on the manufacturers label!! I have rebuilt every failed crap quality test lead in the lab with better quality wire and soldered connections. This 'test lead' rated wire is very flexible and takes a beating BUT real rubber is not a good choice around fuels and solvents found on and around diesel locomotives.