The Meaning Of Surge Protector Uc

First of all, we need to correctly understand what is the Uc value of the surge protector. Uc stands for "maximum continuous working voltage", which means that the surge protector can work for a long time at this voltage, and this voltage will not affect the performance of the surge protector itself.
2. When the UC value of the surge protector is greater than the working voltage of the equipment, will it cause lightning protection failure?
When the circuit voltage exceeds Uc, does the surge protector work? The answer is not. The SPD will only work when it reaches the starting voltage, that is, the "varistor voltage" of the internal varistor.
The following table shows the correspondence between the varistor voltage and Uc. The table comes from "GBT 21431 Technical Specifications for Testing Lightning Protection Devices for Buildings".

From the above table, we can clearly see that the varistor voltage corresponding to the surge protector with a Uc of 200Vdc is 240Vdc. This means that for a surge protector with a Uc of 200Vdc, the surge protector will only work quickly when the voltage on the circuit exceeds 240Vdc.
When a surge voltage of 180Vdc appears in the circuit, a surge protector with a Uc of 200Vdc will definitely not work, but will the equipment with a maximum working voltage of 150Vdc be burned? The answer is no! The reason is: the surge voltage exists in the circuit for a very short time, only a few nanoseconds, just like when the human body briefly contacts the mains, the body will only feel a momentary tingling, and continuous electric shock will cause harm to the body. The same is true for equipment. The surge voltage disappears faster than the equipment reacts, so it will not cause damage to the equipment. Only when the surge voltage reaches the equipment's impulse withstand voltage Uw will the equipment be broken down and damaged. Fortunately, the Up value of the surge protector is always lower than the Uw value of the equipment. For excessively high surge voltages, the surge protector will limit it below the Up value, thereby continuously protecting the back-end equipment from being damaged by electrical breakdown. Therefore, when the UC value of the surge protector is greater than the working voltage of the equipment, it will not cause lightning protection failure.