What length multimeter probes do you recommend? - Page 1
Forum section: electronics / beginners

author: VA3JME
author_rank: Newbie
timestamp: January 20, 2021, 04:41:33 am
content: Yes... I tried search... either I suck at search, or this is a new question!I have a Brymen BM867S which I really love, but unlike it's more expensive brother the BM869S it does not come with silicon probes (it was also about half the price)I was going to order some Probemaster probes, and was almost settled on 48" l(sorry, American company, no Metric) length when a techie friend suggested I might want shorter probes to minimize voltage drop for doing some types of measurements.I use the meter for electronics but also for 12 automotive work.... and was thinking I could keep the 48" probes the meter came with for automotive, and get my ProbeMasters as a shorter set... that way I have the length if I need it... but I was wondering... would a 24" test lead really be that much better than a 48" lead? What length do most people settle on for low voltage electronics, voltage drop tests, etc.

author: SVFeingold
author_rank: Frequent Contributor
timestamp: January 20, 2021, 05:12:24 am
content: Personally I think you'd be annoyed by 2' leads way more often than you'll be hampered by the extra ~25 milliOhms of lead resistance. That's pretty short. Especially for automotive stuff. If you hang your meter from an open hood you won't be able to reach anything in the engine bay, for example.There might be some measurements where it matters...barely. If you're measuring 10A draws from circuits that are sensitive to an ~25 extra milliOhms of load then you might care. For diode testing the currents are very small and voltage drop will be negligible. For resistance testing it'll read a little higher when measuring low resistances, but you can always null it out. Handheld meters with 2-wire measurement aren't great for measuring sub-Ohm resistances anyway.For voltage measurements the input impedance of your meter will dominate. If you were measuring down into the microVolt range on high impedance circuits that are sensitive to probe loading you will probably be using a bench DMM with an input impedance in the gigaOhms.Short version: no I don't think the 2' leads will be better. IMO just get the 4' leads and be done with it. You're not missing anything.

author: bob91343
author_rank: Super Contributor
timestamp: January 20, 2021, 06:20:07 am
content: I think the standard for a long time was 1 meter or three feet for most casual benchtop measurements. A little longer wouldn't hurt, especially in the distant future when the end falls off and you have to cut a bit to repair it.Most of the time the leads get in the way and you wish they were shorter. But during a measurement it's annoying if you are making a test and you pull the device off the bench.

author: Jwillis
author_rank: Super Contributor
timestamp: January 20, 2021, 09:06:11 am
content: A typical DMM won't draw much current on a voltage measurement . A fraction of a microamp . A typical set of probes on a inexpensive meter may have a resistance of a few milliohms . For example a set of probes at 12mOhms at 0.1 microamp each would give a voltage drop less than a fraction of a microvolt . So checking voltages is not much of a problem if you double the probe wire length .Resistance you will have to compensate for resistance of the wire added to the original length since the meter would be calibrated to the probes it was sold with . In most cases the total added resistance is small and not much to worry about . You can re calibrate some DMMs if you like but its not really necessary because the errors will be tiny.Capacitance testing you want as short probe wires as possible. Longer wires can show some fairly high errors in the test.This all depends on the accuracy of the multi meter but in most cases using longer wires won't cause to many problems. Very low resistance , current and voltage readings will give a wider error in the measurement than higher measurements.

author: Ian.M
author_rank: Super Contributor
timestamp: January 20, 2021, 09:28:08 am
content: OTOH if using a handheld multimeter, some short (e.g. 12") heavy duty test leads with croc-clip ends can be very useful when measuring current on the bench. You'll also find you use the short black one a lot with a long red lead when probing round a circuit for voltages relative to ground/0V, just because it reduces the clutter on the bench and the risk of snagging a trailing lead and sending the D.U.T. or multimeter crashing to the floor!

author: The Soulman
author_rank: Super Contributor
timestamp: January 20, 2021, 11:07:38 am
content: Also for automotive use I have additional 2 meter long extension leads and a assortment of grabbers/clamps/probes/magnets etc.When working around a vehicle it is very handy to leave the dmm com terminal connected at the battery minus andbe able to take your meter and probe where you want.Also makes it easier to find grounding issues.For using a handheld meter on the bench I'd like two or three feet long leads, depending on what I'm doing.Imho there is no universal correct length or size of test leads, it all depends.btw, Silicon wire is nice around the bench but not mechanically very robust around sharp objects around vehicles.Again horses for courses.

author: CaptDon
author_rank: Super Contributor
timestamp: January 20, 2021, 04:18:11 pm
content: 4 feet is sort of 'general use' length. Longer leads have many uses but will effect your ability to read very low ohms. Usually you have to touch the leads together and see something like .4 ohms, then when you measure a resistor that reads .9 ohms you will know it is really a .5 ohm resistor and your leads are the other .4 ohms. Very soon you will be making your own 'special purpose' leads with special clips and lengths for dedicated tests, like cars, central air conditioning, house wiring and so on. Best wishes, be safe!!! Most folks will survive a 120vac shock, and 240 is really only 120 each leg to ground. Most folks in the U.S. who tell you they were shocked by 240 really only got 120. The biggest killer is 480/277!!! It will grab you and hold you!! 240 D.C. on Iceland was often fatal also, D.C. just won't let go!! Cheers mate!!

author: Electro Fan
author_rank: Super Contributor
timestamp: January 20, 2021, 06:09:07 pm
content: Quote from: bob91343 on January 20, 2021, 06:20:07 am^^ pretty much this ^^If you had just one DMM and one set of leads roughly 3 feet or 1 meter would be a reasonable length, at least as a starting point. For auto work some extra length (48”) might be useful.Over time you will probably want various leads with different lengths. Often the leads that happen to be on the meter will not be the preferred length so unplugging and replugging happens, and acquiring several or more lead sets happens. And acquiring multiple meters happens. Eventually you will develop a combination that works for you.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 20, 2021, 06:40:17 pm
content: I wouldn't care at all about lead resistance. You just need to decide the tradeoff between leads that are too long and get in the way vs. ones that are too short and don't reach where you need to go. It's better to err on the side of too long. For benchtop use ~2-3 feet seems reasonable. For automotive use a bit longer would probably be handy.

author: bob91343
author_rank: Super Contributor
timestamp: January 20, 2021, 08:05:18 pm
content: The resistance measurement of low values is one important issue. If you are measuring anything below about 10 Ohms it's usually better to do a four wire measurement. Simply subtracting the reading when the leads are shorted isn't a good method, as it depends on the materials and method of connection. You can wobble the plug at the meter and get different readings as well. Most DMMs resolve 0.1 Ohm but that can lull you into thinking the reading is correct.On the other hand, most measurements are tolerant of these errors so you have to decide what works for your needs. Measuring 10,000 Ohms makes unimportant the test leads, unless you are doing high precision.

author: VEGETA
author_rank: Super Contributor
timestamp: January 21, 2021, 12:05:47 pm
content: I prefer the ones that come with it, nothing more. I just need to have croc attachments too.

author: tooki
author_rank: Super Contributor
timestamp: January 21, 2021, 04:13:59 pm
content: Quote from: VA3JME on January 20, 2021, 04:41:33 amThe voltage drop issue has been fully explained, so it really comes down to ergonomics. 3 feet is standard, but on the bench I actually find that too long. (I mean, my bench at work is 1.5m long, so if the workpiece is in the middle, it’s within a 24” radius of the whole bench typically.)What might also be worth considering is getting the shortest length you want for bench use, and then a pair of extension (m-f safety banana) cables for auto use.

author: Ian.M
author_rank: Super Contributor
timestamp: January 21, 2021, 05:28:01 pm
content: Nope. As has already been mentioned, silicone leads don't have the abrasion resistance essential for automotive maintenance use, so as the flexibility of good quality silicone leads is valuable ion the bench, you'd be better off getting separate sets of leads for the bench and the garage, of your preferred length for each application, so your nice bench leads can stay on the bench and not get covered by oil, grease and grit.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 21, 2021, 05:49:44 pm
content: There is no valid electrical reason for lead length on a handheld meter. Long leads get in the in the way on a small bench and short leads end up not reaching measuring points or pulling the meter of its support. You will have to find your own compromise. I find 36" to 48" (1 to 1.25 m) works for me though I do have shorter and longer sets for those special cases.

author: wizard69
author_rank: Super Contributor
timestamp: January 21, 2021, 10:34:09 pm
content: You post a most interesting question because in the end there is no right answer. Consider this example:I work in automation which means a lot of work done in large electrical panels. Short test leads in these sorts of areas are extremely frustrating to say the least. However long leads often turn into a tangled rats nest. There is no perfect length. At the bench you of course have lots of options, including patch cords and test specific wired harnesses.So in a nut shell you should look at any set of leads you buy as a starting out set if you have nothing now. Patch cords and short application specific leads will be added to your inventory. At work I've had to resort to grabbing a length of MTW to ring out circuits in drag chains and the like. You really can't expect a general purpose test lead set to cover every issue you might run into.As for your friends comments about induced errors from long test lead wires - Maybe! Over the years I've seen some pretty pathetic test leads supplied with meters. A quality set, built with a suitable heavy gauge of wire, should not be a problem with a handheld meter. As others have pointed out already, where it might matter you have to consider that maybe you are using the wrong type of meter anyways.

author: David Hess
author_rank: Super Contributor
timestamp: January 22, 2021, 04:15:13 pm
content: Quote from: Ian.M on January 20, 2021, 09:28:08 amI usually cut the negative probe off of probe sets and replace just it with an alligator clip so I have one alligator clip and one needle probe.