How to manually check electrical wires for polarity.

Multimeters can be confusing and scary for first timers. That pretty much goes for anything you use for the first time, I suppose. But you may get scared away by all the symbols and meanings and different configurations that are on multimeters, if you’ve never used one before.

But how did you learn to drive? You had to learn all the traffic symbols and rules before you successfully hit the road. Same deal here. Crack the encryption and begin to learn the language and you’ll wonder how anyone could be scared of this wonderful little tool.

So I hope to begin writing some basics of using a Digital Multimeter blog on here as well. Probably giving it another category such as Tutorials/Walkthroughs or something of the like.

In this blog I’d like to just give one or two quick basics to handling and reading a Digital Multimeter. Something quick and direct for the first timers, as I myself once was.

The following will be a walkthrough on how to check the polarity of circuits (wiring) with a Digital Multimeter. I can only walk you through Digital Multimeters because I’ve never used an Analog Multimeter (I’m so nu skool!).

Okay, so the first step to doing anything with electrical devices or electrical circuits is to take those saftey precautions. Don’t electricute yourself or damage your home appliances because you got bored and wanted to see the voltage of your microwave. Please follow all saftey rules in your Digital Multimeter’s manual, or the ones you found online. I’m no where near responsible for anyone’s mistakes, proceed with caution and at your own risk!

The first thing to know about Multimeters is that they are just as fragile as the circuits you are testing them on. Don’t test a little cheapie multimeter on something that’s drawing in 100 amps of electricty and set it to 10 amps. It will fry your multimeter and then break and maybe even cause damage to you. Know your Multimeters limitations and play by them.


Today we will be testing wiring for polarity. What does that mean?

It means that the wires were not marked or there is absolutely no indication which wire is Positive (+) and which wire is Negative (-). This will be essential to know the correct polarity if you are testing circuits and devices to ensure that the device is working correctly or not. Or if you must go in and rewire or something, you must know the correct polarity or the device will not work when you are finished repairing it. Today’s wiring is indication somehow someway by the negative wire having somekind of indication on it. But as I stated before, this is just a simple test for someone to get used to using a Multimeter.

Pretty simple.

So turn on your Digital Multimeter and connect the Negative (-) lead to the COM port. Then connect the Positive (+) lead to the V/mA port. Make sure to set your settings to the next highest rating of voltage. For this example, since I’m testing the wiring of a 1.5v DC wire, set the DCV to 20V.  I set it this way because it’s the lowest setting of that range on my Multimeter that I’m using.

Then simply touch your Positive and Negative leads to the wire. You will get a numerical reading regardless of the polarity. But the point of this exercise is to make sure we know the polarity of the wires. If you see a Negative (-) sign flashing before the numerical value, you are recieving a “negative” reading. This means your leads are in the incorrect polarity positions on the circuit (wires). Switch the leads to the opposite wires. You should get the same numerical reading, just without the flashing negative signal before them. You have corrected the polarity, and the multimeter’s leads are attatched to the correct polarity. This means that whatever wire the Postive (+) lead is connecting to at this point, is a Positive wire. The lead connecting to the other wire is telling you, the wire is negative.

The simplist version of this test is for speaker wire. If the polarity is reversed, the sound output to the speakers will be noticable. If the polarity is correct, the sound will be normal. Once again, if you reverse the polarity on your speakers, no harm will be done, it will just sound bad. Simply reverse the polarity to regain proper sound.

Explore posts in the same categories: Electronics Repair

5 Comments on “How to manually check electrical wires for polarity.”

  1. khan Says:

    wow so simple explanation real easy to understand ,much appriciated and many thanks to make life easy

  2. steve Says:

    very helpfull

  3. Ac Says:

    Thank You! This really did help me out a lot. I was wiring speakers into my car, and the wires were all different colours. I got it wrong (based on a forum post) and speakers didn’t sound good, then tested them and needed to switch them all. Now great sound and volume!!

  4. Andrew Durso Says:

    Very helpful, thank you

  5. Al Allen Says:

    Thanks for the help. I had heard that LED lights could be damaged if connected improperly; now I can get it “right”.

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