A voltmeter is one of the most useful tools for measuring home electricity, especially when you use it properly. Before using a voltmeter for the first time, know how to properly set up the instrument and try to test it on a low-voltage circuit, such as a battery.
This article describes how to measure mains voltage. You may also be interested in measuring flow and electrical resistance using a multimeter.
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Part 1 of 3: Setting Up Tools
Step 1. Set your instrument to measure mains voltage
Most voltage measuring devices are actually multimeters that can measure some aspect of an electrical circuit. If your tool has knobs with multiple settings, adjust them as below:
- To measure the mains voltage in an AC mains circuit, set the knob to V~, ACV, or VAC. Most residential electrical circuits are alternating current (AC) electricity.
- To measure the mains voltage on a DC power circuit, select V–, V---, DCV, or VDC. Batteries and portable electronics are usually direct current (DC) electricity.
Step 2. Choose a power range that is larger than the mains voltage you are measuring
Most voltmeters have several options for mains voltage, so you can change the voltmeter's sensitivity to get a precise measurement and avoid damaging the instrument. If your digital voltmeter does not have a choice circuit, then with the "autoranging" feature, the digital voltmeter can detect the correct voltage range automatically. Follow the guidelines below:
- Choose a power range that is higher than the maximum utility voltage you are measuring. If you do not know the maximum mains voltage, select the highest electrical range to prevent damage to the appliance.
- On the battery is usually written large power supply voltage, which is about 9V or less.
- A car battery has about 12.6V when fully charged and with the engine not running.
- Most countries in the world have 240V and 120V power outlets in America and some countries.
- mV comes from the word millivolt (1/1000 V), is sometimes used to denote the lowest setting
Step 3. Insert the probe cable
Your voltmeter will come with one black and red probe wire. Each probe wire has a metal on one end and a metal jack on the other that will fit into the jack holes on your voltmeter. Insert the cable into the jack hole following the guidelines below:
- The black jack should always be inserted into the hole labeled "COM."
- When measuring the mains voltage, insert the red jack into the hole labeled V (among other symbols). If there is no V symbol, select the hole with the smallest number or the one with the symbol mA.
Part 2 of 3: Measuring Voltage
Step 1. Carefully hold both ends of the cable
Do not touch the metal end of the probe when connecting it to an electrical circuit. If the insulating rubber on the end of the cable looks damaged or torn, wear insulating gloves or purchase a new probe.
The two metal ends of the probe wire must not touch each other while being connected to an electrical circuit or it will cause a large electric spark
Step 2. Touch the black probe wire to one part of the electrical circuit
Measure the electrical circuit voltage by touching the two probe wires to the circuit in parallel. In other words, you touch the ends of the two probe wires at two points in a closed electrical circuit that carries an electric current.
- On the battery, touch the black probe wire to its negative terminal (anode).
- In the socket, touch the black probe wire into the neutral hole or the hole on the right.
- If possible, disconnect the black probe cable before proceeding to the next step. Most black probe wires have small plastic bumps that can stick to the socket.
Step 3. Touch the red probe wire to different points on the electrical circuit
With this, a parallel electrical circuit will be made and cause the voltmeter to show the magnitude of the mains voltage.
- On the battery, touch the black probe wire to its positive terminal (cathode).
- In the socket, touch the red probe wire into the "phase" hole or the hole on the right.
Step 4. Increase the measuring range if you get an excess measurement result
Immediately increase the measurement range to a higher setting if you get a result like the one below before your appliance breaks down:
- Your digital device shows "OL", "overload", or "1". Note that "1V" is the correct measurement, so you don't have to worry about your voltmeter being damaged.
- Your analog hand points to the opposite side of your scale.
Step 5. Adjust your voltmeter if needed
You may need to adjust your voltmeter if the digital voltmeter shows 0V, shows nothing, or the analog voltmeter needle doesn't move at all. If there are no readable results, try doing the things below:
- Make sure both probe wires are connected to the electrical circuit.
- If you're measuring DC electrical circuits and getting no results, look for the small knobs or buttons on your appliance labeled DC+ and DC- and move them to a different position. If your device does not have this option, swap the red and black probe wires.
- Reduce the mains voltage range one option below. Repeat this step until you can read the measurement result.
Step 6. Read the voltmeter
The digital voltmeter will clearly show the electric voltage on the electronic display. Reading an analog voltmeter is a little tricky, but it becomes easier once you understand how. Read the next section for how to read an analog voltmeter.
Part 3 of 3: Reading Analog Voltmeter
Step 1. Locate the voltage scale on the scale board
Choose one that matches the setting you have selected on your voltmeter knob. If none of the choices match, read from a scale that is easy to multiply.
For example, if your voltmeter is set to DC 10V, look for a DC scale with a maximum of 10. If not available, look for a DC scale with a maximum of 50
Step 2. Estimate the needle position based on the closest number
This scale is a linear scale like a ruler.
The needle pointing midway between 30 and 40 is read as 35V
Step 3. Share the results you got if you used a different scale
Skip this step if you are reading from the exact same scale as your voltmeter setting. If not, improve your answer by dividing the maximum value on the scale you used by the number on your knob choice. Divide the number pointed to by the needle by the previous division result to get the actual voltage.
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For example, if your voltmeter is set at 10V, but you read it on a 50V scale, calculate 50 10 =
Step 5.. If the needle shows 35V, your answer is 35
Step 5. = 7V.
