Many people often find such a problem when selecting surge protectors: Why is the line voltage 380V or 440V, and the surge protector model Uc value chosen by the surge protection manufacturer is only 275V or 320V? The working voltage of the surge protector is less than my voltage value, so can the selected surge protector be lightning proof when installed on the line?
In fact, there is a misunderstanding about the voltage parameters of surge protector selection, that is, the difference between phase voltage and line voltage.

What is the relationship between phase voltage and line voltage? Why does my surge protector work when the Uc value is less than the line voltage? Below, Xiaobian will give you popular science under these two concepts.

1. What is phase voltage and line voltage?
For example, in a three-phase five-wire power supply system (such as TN-S zero protection system), which is composed of three phase lines and a neutral line and a PE line, then in this three-phase five-wire power supply system, the phase voltage refers to any phase line and the neutral line (N line), any phase line and the voltage between PE line; Line voltage refers to the voltage between any two phase lines. As indicated in the following figure:

The voltage between L3 and PE line is phase voltage, and the voltage between L3 and N line is also phase voltage.
The voltage between L1 and L2 lines is the line voltage.
2, the relationship between phase voltage and line voltage
The standard AC voltage commonly used in China is: phase voltage is 220V, line voltage is 380V, and the mathematical relationship between phase voltage and line voltage is: line voltage is √3 times of phase voltage.
3, why the surge protector Uc value is less than the line voltage can work normally?
First of all, let's understand the working principle of the surge protector: the installation position of the surge protector is between the phase line and the neutral line, the phase line and the ground line, the 3PN surge protector will also be installed between the neutral line and the ground line, and the surge protector will not be installed between the two fire lines in any case. Therefore, when we select the surge protector, we only need to consider the phase voltage in the circuit when selecting the Uc value.

Therefore, when you select and install the surge protector, the circuit voltage you see is 380V, while the actual phase voltage is only 220V, and the lightning protection device with Uc of 275V or 320V can fully achieve the lightning protection effect. If the line voltage is 440V, then its phase voltage is 254V, and the installation of 320V surge protection can also meet the lightning protection requirements in this circuit system.
When the surge protector is selected, the continuous working voltage Uc is used as the line to ground working voltage X1.2 times, which is enough to protect the circuit. If the continuous working voltage is too high, the residual voltage will be too high, reducing or losing the protection effect.