How to Test a Wire for Voltage in 5 Steps
Wires are the blood vessels of electronics, supplying vital energy to critical components. So testing a wire for voltage can tell you a great many things about the health and functionality of power cords, switches, receptacles and much more. For one, it can help electricians determine if an outlet or electrical device is safe to work on or reveal the culprit behind a short circuit. Believe it or not, testing voltage in wires is also a troubleshooting technique used to find the source of electrical malfunctions that could prevent your appliances or machines from working properly.
So without further ado, we’ll tell you how to test a wire for voltage using a multimeter and voltage detector.
Supplies You’ll Need
- Voltage tester
- Rubber voltage gloves
How to Check Voltage with a Multimeter
So you want to know how to test a wire for voltage, but maybe you don’t know how to safely use a multimeter or identify neutral vs. ground vs. hot wires. Not to worry. In this section, we’ll teach you how to test a wire for voltage with a digital multimeter.
- Step 1. Attach the test leads – First, you’ll want to attach the test leads to your multimeter. Plug the neutral (black) test lead into the COM outlet and the positive (red) test lead into the voltage terminal. Next, set the dial to volts AC (this is indicated by a sine wave).
- Caution: Before using, always make sure the insulation is fully intact on both the case and test leads. Touching exposed metal on your multimeter could result in shock or electrocution.
- Step 2. Set the voltage range – If you have an auto-ranging multimeter, you don’t have to worry about this step–your multimeter will automatically calculate the voltage. Otherwise, you’ll have to set the dial to the voltage one range above what you’re testing.
- Caution: Double-check that your multimeter, including your test leads, is rated to withstand the voltage range you’re wanting to measure.
- Step 3. Ground your neutral test lead – Touch your neutral (black) test lead to the ground wire. If you are unsure which wire in the circuit is ground, you can touch your test lead to any grounded object.
- Note: You can also check for voltage by connecting your neutral test lead to a neutral wire
- Step 4. Connect the positive test lead to the wire – Touch your positive test lead to the exposed part of the wire. The number of volts will now display on the screen. If the multimeter reads zero, no voltage is present in the wire.
- Caution: Never touch the test lead’s tips or bring them in close contact next to an exposed wire without grounding one of them first.
- Step 5. Dissemble your multimeter – After use, remove the test leads in reverse order. That is, red first, black second.
How to Identify Neutral Wire with Multimeter
In the US, neutral wires are typically color-coded by voltage. 120 volt, 208 volt and 240-volt wires usually sport a white sheathing, whereas 277 volt and 480 volts are gray. Some neutral wires are conveniently labeled with “N” or “Neutral”. You can also test the wire with your multimeter following the same procedures as described above. Neutral wires have voltage readings close to zero.
Note: You shouldn’t rely on color coding alone, as sometimes the color and voltage vary, especially if you’re working on an electrical device manufactured outside the US.
How to Find Hot Wire
The phase line wires can come in a variety of colors, including black, red and blue for 120, 208 and 240 volts. For 277 and 480 volts they can be either brown, orange, yellow or red. With so many color combinations, it can be difficult to identify which wire is hot. To test for it, follow the same procedures as above. If you get a voltage reading, congratulations, you’ve found the hot wire!
How to Find Ground Wire
Ground wires with 120, 208 or 240 volts are typically a solid green, whereas a 277 or 480-volt ground wire is an alternating green and yellow. Again, this is a loose rule of thumb rather than a one size fits all absolute.
There should be no voltage in the ground wire if it is properly grounded. However, finding the ground wire is a little trickier, so here’s an article on how to identify the ground wire.
Can You Test a Wire with a Voltage Tester
Yes, you can test a wire with a voltage tester. The only difference between using a voltage tester and a multimeter is a voltage tester won’t display the number of volts present. Rather, they’ll beep or light up if they come in contact with or detect voltage. They’re also not as accurate so be sure to double-check the reading with a multimeter if you plan on working on the wires.
But how do you test a wire for voltage? We’ll tell you exactly how you can do that with a non-contact voltage tester.
Step 1. Make sure your voltage tester has fresh batteries – if it’s been a while since its last use, you’ll want to either replace or test your batteries since using undercharged ones can result in false readings.
Note: You can test your batteries with a multimeter by connecting the neutral test lead to the neutral terminal and the positive test lead to the positive terminal. Switching the leads will give you a negative value reading. If this happens, just do a quick switch-a-roo. A fully charged battery will read 1.5 volts, whereas a weak battery will give you a reading of 1.2 volts.
Step 2. Bring the voltage tester near the wire – Because this is a non-contact voltage tester, you don’t need to directly touch the tip to the wire. But be careful! Voltage testers are known for picking up phantom readings, so make sure the tester isn’t near other wires that could give it a false reading.
If at any point you are unsure of the procedure, you should stop immediately and contact an authorized service technician. Even though homes are only powered on 120 volts, any more than 50 is enough to cause serious injury and even death should you come in direct contact with a live wire. For this reason, you should always wear the necessary personal protective equipment and take preventive safety measures when working with electricity.