To test the voltage of an AC circuit, set the knob to V~, ACV, or VAC. Household circuits are almost always Alternating Current. To test voltage of a DC circuit, choose V–, V—, DCV, or VDC. Batteries and portable electronics are typically Direct Current.
Choose a setting higher than the maximum expected voltage. If you have no idea what to expect, choose the highest setting to avoid damaging the device. Household batteries are usually labeled with the voltage, typically 9V or below. Car batteries should be at approximately 12. 6V when fully charged with the engine off. [2] X Research source Household outlets are typically 240 volts in most of the world, and 120 volts in the US and some other countries. [3] X Research source mV stands for millivolt (1/1000 V), sometimes used to indicate the lowest setting.
The black jack always plugs into the hole labeled “COM. " When measuring voltage, plug the red jack into the hole labeled V (among other symbols). If there is no V, choose the hole with the lowest number, or mA.
The two metal probes should never touch each other while they are connected to a circuit, or severe sparking could result.
On a battery, touch the black lead to the negative terminal. In a wall outlet, touch the black lead into the neutral hole, which in the US is the larger vertical hole, or the vertical hole on the left. [5] X Expert Source Ricardo MitchellElectrician & Construction Professional, CN Coterie Expert Interview. 6 May 2020. Whenever possible, let go of the black test lead before moving on. Many black probes have a small plastic bump that can stick into an outlet.
On a battery, touch the red lead to the positive terminal. In a wall outlet, fit the red lead into the “hot” hole – in the US, this is the smaller, vertical hole, which is usually on the right. [6] X Expert Source Ricardo MitchellElectrician & Construction Professional, CN Coterie Expert Interview. 6 May 2020.
Your digital display reads “OL,” “overload,” or “1. “[7] X Trustworthy Source Science Buddies Expert-sourced database of science projects, explanations, and educational material Go to source Note that “1V” is a real reading, and nothing to worry about. Your analog needle shoots to the other side of the scale.
Make sure the test probes are both connected to the circuit. If you are measuring a DC circuit and get no result, look for a small knob or switch on your device labeled DC+ and DC- and move it to the other position. [8] X Research source If your device does not have this option, reverse the positions of the black and red probes. Reduce the range by one setting. Repeat if necessary until you get a real reading.
For example, if your voltmeter is set to DC 10V, look for a DC scale with a max reading of 10. If this isn’t available, find one with a max of 50.
For instance, a needle pointing halfway between 30 and 40 indicates a reading of 35V.
For example, if your voltmeter is set to 10V but you are reading off a 50V scale, calculate 50 ÷ 10 = 5. If the needle is pointing at 35V, your actual result is 35 ÷ 5 = 7V.
