Do the common mode and differential mode of the surge protector correspond to the L/N-PE or L-N protection mode?

When selecting surge protectors, we often encounter various protection modes, such as 4P, 3P+N, L-PE, N-PE, and L-N.

So, do the common-mode and differential-mode protection modes of surge protectors correspond to L/N-PE or L-N protection modes?

1. The common-mode protection of a surge protector corresponds to L-PE and N-PE protection modes, i.e., protection between phase-to-ground (L-PE) and neutral-to-ground (N-PE). Differential-mode protection corresponds to L-N protection mode, i.e., protection between phase-to-neutral (L-N).

2. Both differential-mode and common-mode protection of surge protectors are necessary, and it's impossible to simply say which is more important. Their respective functions are as follows:

① Differential-mode protection: Differential-mode protection mainly targets interference between internal circuits of equipment, such as interference between power lines or signal lines. When there are interference sources between internal circuits of equipment, the differential-mode protector can suppress these interferences by discharging differential-mode current, thereby protecting the normal operation of the equipment.

② Common-mode protection: Common-mode protection primarily targets damage to equipment caused by external interference sources such as lightning. When equipment is affected by external interference sources such as lightning, the common-mode protector can suppress these interferences by discharging common-mode current, thereby protecting the normal operation of the equipment.

Therefore, both differential-mode protection and common-mode protection are necessary, and the appropriate protection method should be selected based on the actual situation. In some cases, differential-mode protection may be more important, such as equipment operating in a strong electromagnetic environment; while in other cases, common-mode protection may be more important, such as equipment operating in areas prone to lightning.

3. Is differential-mode protection sufficient for AC systems using SPD surge protectors?

When selecting SPD surge protectors for AC systems, differential-mode protection alone is insufficient. Differential-mode protection mainly targets interference between internal circuits within the equipment and cannot effectively suppress damage caused by external interference sources such as lightning.

Therefore, to comprehensively protect the AC system, both differential-mode protection and common-mode protection should be used simultaneously.

Common-mode protection primarily targets damage to equipment caused by external interference sources such as lightning, suppressing these interferences by discharging common-mode current. In AC systems, differential mode protection is essential due to the voltage difference between the live and neutral wires.

Differential mode protection primarily targets interference between internal circuits within equipment, suppressing this interference by discharging differential mode current. Simultaneous use of both differential mode and common mode protection can better protect AC systems, reducing damage to equipment from external interference sources such as lightning, and improving equipment reliability and stability. Therefore, when selecting surge protectors, the needs for both differential mode and common mode protection should be comprehensively considered, choosing a surge protector with comprehensive protection functions.

Induced lightning surges damaging equipment are generally caused by line-to-ground common mode breakdown. When the surge protector's lightning protection module cannot withstand the lightning surge energy at the installation location, the product will be damaged and degraded, and the internal varistor chip may break down. When the surge protection module is broken down by lightning, the voltage across its terminals will be zero, and the surge protector will be in a short-circuit state. At this time, if the load connected in parallel is still energized, current will flow into the ground through the surge protector, leading to line-to-ground common mode breakdown. Therefore, when selecting and using surge protectors, attention should be paid to their protection level and installation location to ensure that they can effectively protect equipment from induced lightning surges.