One of the main functions on a digital multimeter is testing wires.
The difference between a live wire and one that doesn’t have a current flowing through it can be huge. As you probably know, you never want to work on exposed wires if they’re “live”, meaning that they have an electrical current flowing through them.
The best way to avoid this is by turning off the corresponding breaker in the breaker box.
But sometimes, electrical circuits aren’t laid out the way you expect. Maybe you’re working on an unfamiliar house, still figuring out the exact configuration of the breaker box or you just want to be extra sure.
In this blog post, we’ll guide you through the different steps to know exactly how to test a wire for power with a digital multimeter.
First, we’ll look at the different types of voltage you may come across and then we’ll discuss the practical details for two types of multimeters.
Different types of voltage
In general, there are two types of voltage. There is Direct Current (DC) and Alternating Current (AC). In the United States, these two types are used in different situations.
Direct current is an indication of a power source from which current flows in one direction.
Generally, everything that is powered by a battery is direct current. This doesn’t just include small appliances, but also your car, boat, or any other device that runs on a big battery.
In alternating current, as the name suggests, the electric charge (current) changes direction every now and then. You can find alternate current whenever you plug something into the wall, and it is also the current that is delivered to your house by the electrical company.
In alternating current, the electric charge is like a wave (similar to sound). A clear wave is called a sine wave.
When you need to test a wire for power, you’ll usually need to tell your multimeter if you’re going to be testing a DC or AC current.
There are some (advanced) digital multimeters that can do it for you, but unless you’re absolutely sure your multimeter comes with this special trick, you can safely assume that it’s up to you to select the correct setting.
A last note about the two types of current is that alternating current packs much more of a punch than DC current. You can probably relate to this when you realize that you’ve been warned forever to not mess with the outlets (starting with outlet covers for crawling babies).
On the other hand, batteries have a much safer image, and for good reasons.
Now that we’ve covered the basics of the different types of electrical current, we’ll discuss how you can use a multimeter to test a wire for power.
How to test a wire for power with a multimeter
There are four steps to go through to test a wire for power with a multimeter. Although different types of multimeters can have more or fewer functions, you can safely assume that your multimeter is equipped to test a wire for power.
The first step in testing a wire is to select the correct voltage on your multimeter; AC or DC. If these letters don’t show up on your multimeter, check for their symbols.
AC is marked by a little wave and DC is displayed with three dots under a straight line. Select the voltage (V) setting with the correct current next to it. If there are different settings for each current, don’t worry, as we’ll select the correct range in the next step.
Some multimeters are auto-ranging, which means that they automatically select the range in which to measure the current. A lot of basic models are manual ranging, which means that you have to select a range to measure in.
If you don’t know the range you’ll be measuring in, start with the highest setting and work your way down from there. You want to end up in a range that is higher than what you’re measuring, but as low as possible. To measure a 9V battery, for example, you’d use a 20V range, instead of a 200V range.
Now that you’ve selected your (initial) range and the correct current, make sure to double-check your leads. Ensure that they’re in the correct slots and they’re all the way in. This eliminates a lot of problems that might come up with your readings.
Now, put the ends of the leads at the wire that you’re testing. Avoid touching the wire with your fingers. Not only could this influence the reading, but it might shock you, too. Wait a few seconds, and the reading will show up on your display.
If you want to check if there is a break in a wire, watch this video:
How to test a wire for power with a multimeter without making contact
Some advanced digital multimeter models have a contactless voltage meter. Depending on the precise model, the execution may differ. In general, you press the non-contact voltage button and hold the top of the multimeter close to the source you want to measure.
In the simplest form, your multimeter will beep and alert you that the wire you are testing does indeed have power flowing through it. As you can imagine, this feature is great for technicians and electricians you deal with live wires a lot and need to establish live wires in an instant (the safe way).
Conclusion
In this article, we have discussed everything you need to know to test a wire for power with a multimeter. First, we went over the two different types of current you can encounter.
Then, we discussed the different ranges you can select on a manual ranging multimeter and how to go down the scale if you’re not quite sure which range to select at first.
Lastly, we showed you the two different ways to test a wire for power, one with a classic multimeter with leads, and another way with a more advanced type digital multimeter that has a non-contact voltage meter function.