Voltage, also known as potential difference and electromotive force, is the point difference between two points. In an electrostatic field, it is equivalent to the work per unit of charge required to move the charge being tested from the first point to the second point. In international units, voltage is measured in volts, a term that Honours the Italian physicist Alessandro Volta.

Definition of Voltage

The definition of voltage is that a negatively charged object will be pulled in the direction of higher voltage, while a positively charged object will be pulled in the direction of lower voltage. The regular current that can be seen in life in a wire or resistor flows from the direction of higher voltage to the direction of lower voltage. The higher the voltage the more current will flow to the electronic device, but be aware that too high a voltage will damage the circuit, and too low a voltage will cause the circuit to not work, so that the electronic device can not operate.

Classification of voltage

1 Voltage is divided into high voltage, low voltage, safety voltage according to the size.

1.1 High voltage

High voltage is defined as distribution lines exceeding 1000 volts AC or 1500 volts DC. (Note: DC is the flow of current without any change in the direction or magnitude of the current. For example, if a light bulb is connected to DC, the bulb will emit a uniform light. (Alternating current is a periodic change in the direction and magnitude of voltage and current, e.g. household power sockets, where the voltage and current change in different forms.)

1.2 Low Voltage Electricity

Low voltage electricity is defined differently in different countries. According to the standards of the International Electrotechnical Commission, low voltage electricity is 50 to 1,000 volts alternating current and 120 to 1,500 volts direct current.

1.3 Safe voltage

Safe voltage is the voltage that does not cause immediate death or disability, and the safe voltage that permits continuous exposure under normal conditions is 36 volts.

2 Voltages are categorized by function into impedance voltages and medical voltages

2.1 Impedance voltage

Impedance voltage, also known as short-circuit voltage, represents the voltage loss across the transformer’s own impedance when the transformer passes the rated current. Note: A transformer is a device that utilizes the principle of electromagnetic induction to change the AC voltage.

2.2 Medical Voltage

The voltage referred to by the ECG is the distance between two transversals on the ECG paper. An ECG records electrical signals in the heart and helps diagnose arrhythmias.

Why voltage is important

Voltage is an important indicator of electrical energy, and technicians need to know the voltage of a circuit when dealing with most malfunctions. A multimeter is usually used to measure the voltage and determine if there is a malfunction based on the voltage difference of the circuit. When there is a clear voltage difference between the two ends of the line, it can be shown that there is a broken circuit fault, you can use the ohm file of the multimeter to determine the fault, when the measured resistance is infinite, it can be confirmed as a broken circuit fault. When the measured voltage of the circuit is 0 volts, there may be a short circuit or false connection phenomenon, you need to use the multimeter ohm gear to determine the fault. 

So voltage is very important in our life, unqualified voltage will cause serious harm to the power grid, voltage displacement deviation will affect daily work, damage to electrical equipment, and even cause voltage collapse.

How to measure voltage

When measuring voltage, the digital multimeter is most often used in our daily life.

1.How to use digital multimeter to measure voltage correctly

1.1 The digital multimeter has a red lead and a black lead, first of all, you need to insert the red lead into the input of the digital multimeter labelled with voltage V and insert the black lead into the input of the multimeter labelled with COM, which is grounded.

1.2 Depending on what is being measured, use the dial in the center of the multimeter to select DC (direct current) or AC (alternating current) mode. Note: DC means DC with three dots or straight lines underneath and AC means AC with wavy lines underneath.

1.3 You also need to select the measurement range. Depending on the different ranges you need, you can look up the normal voltage you are measuring in the user’s manual, and then select the appropriate measurement range to measure.

Common values of voltage

1. A lead acid battery has a voltage of 2 volts

2. The voltage of a household circuit in China is 220 volts, and the household voltage in Japan and some countries in the Americas is 110 volts.

3. The nominal voltage of an alkaline battery is 1.5 volts.

4. The voltage that maintains bio-current in the human body is 1.2 millivolts.

5. The safe voltage for the human body is not higher than 36 volts

6. The voltage of a home storage battery is 48 volts

7. The voltage of a car battery is 12V