Can you damage a multimeter if it's set to DC and you measure AC? - Page 1
Forum section: electronics / beginners

author: jharbuz5
author_rank: Newbie
timestamp: April 24, 2013, 01:03:48 am
content: I was fixing my coffee maker and I needed to measure voltage to a water valve. There were 2 small wires (24 AWG) 1 red and 1 black making me think it would be sending a DC voltage (in my experience AC wires do not have the positive / negative color coding, and they are usually not this small). I used my Fluke DMM 179 and put the probes on when it was set to measure DC voltage. I noticed the bar graph below the reading jumping back and forth all over the place with no stable reading being shown. Then I knew it was an AC voltage. I switched the meter to AC and sure enough, 123 AC volts was shown. Long story short I fixed the coffee maker and sure enough a full 120 volts AC is in fact driving that water valve. I didn't measure it, but with the wires being so small it must be a very small AC current that traverses them.The meter seems to be working just fine, butmy newbie question is can you damage your multimeter (or make it less accurate) by setting it to DC volts and then measuring AC volts?. The Fluke 179 has only 1 DC and 1 AC volts setting and then it normally auto ranges from 1 to 1000 volts, so it's not like I had a manual meter set to measure 10 volts and then put the 123v across it.I'm thinking the answer is no but just thought I would make sure. I've always loved how accurate the 179 is, and it would irk me big time if what I did will negatively affect its accuracy going forward.

author: IanB
author_rank: Super Contributor
timestamp: April 24, 2013, 01:19:03 am
content: You won't hurt the meter.In principle you can connect that meter to the mains while set on the ohms range and still not damage it (but I don't recommend you try it, even so).

author: Lightages
author_rank: Unknown
timestamp: April 24, 2013, 01:44:37 am
content: If a meter meets its CAT ratings correctly under the current rules, then probably there is no problem. It is a little complicated however. Some meters are still being sold under the old CAT rating rules and as such they have slightly different and lower requirements.A CAT rating is mainly for the protection of the user, not the meter. So if your meter is rated at CATII/600V right now it is supposed to be able to take 600V on any jack with any function without causing harm to the user. This does not guarantee the proper function of the meter above this voltage. Some meters have the proper safety ratings but also have a maximum voltage for a specific function. Any meter that claims 600V should take this on the AC ranges and the DC ranges without harm to the meter. A meter might specify less voltage for the proper function of the meter on Hz for example. If you apply 600V to a meter on its HZ range and it is only rated for 30V then it might not survive on that function and not indicate any correct readings on Hz anymore.There is a clause though that appears to say that, regardless of the failure in any other mode, voltage modes must survive the torture test used for the specific CAT rating the meter has and it must still show the correct voltage so as to indicate the presence of dangerous voltages.So the short answer is no. Measuring a voltage within the spec of a meter in AC or DC whether that is the actual type of current will not harm your meter. How else would you know if you have DC or AC sometimes? The long answer is it can depend on the meter and the function selected, ie: AC mV vs DC V, or according to what the manual says for that specific model. If it is a $5 meter then all bets are off. If it is a Fluke 87V then do almost anything you want on any range within the voltage rating of the meter.Oh yes, some things to read on the subject of meter safety:https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/andhttps://www.eevblog.com/forum/projects/cat-ratings-and-interpretation/but if you are using the Fluke 179 then the really short answer is yes, use it on DC or AC to check any voltage or type of current flow up to its highest voltage rating without worry.

author: jharbuz5
author_rank: Newbie
timestamp: April 24, 2013, 01:52:36 am
content: IanB, Lightages, Thanks for the replies!Lightages, this was a fluke 179 and it's almost identical to the fluke 87V (I own both). Fluke 179 is just missing a couple of measurement functions the 87V has. Good point about the mV setting. In my case I had it set to the standard DC volts setting not the mV. The 179 is 1000V Cat III & 600V Cat IV rated just like the 87V. Thanks for all the detail.

author: ttp
author_rank: Regular Contributor
timestamp: April 24, 2013, 04:46:12 am
content: You can measure DC and keep swapping leads, all it happen the "-" sign will flicker. Measuring AC is not much different, the only difference is you cannot easy get a meanigfull reading on DC range as you've found out.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: April 24, 2013, 06:01:30 am
content: nope , fluke are good quallity company and you really can't harm the meter by doing so .You've got a fluke meter in your hands . by all means ... you should have known fluke's repretition ... i know you are newbie ... so you should be awear, fluke are well well known for they're durabuillity versuse any abusing .Long story short - no matter what range you selected ... you can be sure .. the meter wont be damegd , unless litning would have stroke him o_Oadit: sorry for me being such a dick - I fixed it ( I hope )cheers

author: smashedProton
author_rank: Frequent Contributor
timestamp: April 24, 2013, 07:07:02 am
content: Yes, unless you jam the leads into the wall socket when the leads are in the amps jack. I did that as a kid and got a nasty surprise. The meter still worked after I reolaced the fuse. Gotta love fluke!

author: Balaur
author_rank: Unknown
timestamp: April 24, 2013, 07:18:08 am
content: Quote from: eevblogfan on April 24, 2013, 06:01:30 amAre you the new Kiriakos?Come on, your posts start to get ridiculous. The OP asked a nicely formulated question; his approach is sound; he invested time and attention in carefully stating his request. Then, he got pretty solid answers.Then, behold your personal contribution: a very poorly phrased answers, highly opinionated, with errors every second word and some words so far from the original form that they are not even recognizable.Even ignoring the form, you are not contributing to the thread; you are diminishing the SNR of the forum. I know that you are young and enthusiastic, I like your energy, but please invest some effort in your posts. You and your contributions will be liked even more.Best regards,Dan

author: retiredcaps
author_rank: Super Contributor
timestamp: April 24, 2013, 08:11:00 am
content: Quote from: IanB on April 24, 2013, 01:19:03 amDave did an ohms overload test with a bunch of multimeters in his lab.http://www.eevblog.com/2012/03/04/eevblog-252-multimeter-ohms-overload/The results varied, but none died.