A common method for overvoltage protection of Solid State Relays (SSRs) is to connect metal oxide varistors (MOVs) in parallel.

The area size of MOV determines the absorbed power, and its thickness determines the protection voltage value. When the peak voltage applied to the AC terminals of a solid-state relay exceeds the maximum voltage peak it can withstand, it may cause voltage breakdown and damage to the components inside the solid-state relay. By paralleling MOVs, it is possible to absorb some of the overvoltage energy in the event of overvoltage, thereby protecting solid-state relays.

Generally speaking, solid-state relays in the 220V series can be equipped with varistors ranging from 500V to 600V; The 380V series solid-state relay can select varistors ranging from 800V to 900V; The 480V series solid-state relays can be equipped with varistors ranging from 1000V to 1100V.

In addition, solid-state relays usually have an RC absorption circuit for internal protection. But in some places with high reliability requirements, such as power compensation capacitor switching, motor forward and reverse rotation, in addition to the above protection measures, other stricter protection measures need to be taken.

In practical applications, it is also important to select solid-state relays with appropriate voltage levels based on the type of load (resistive, inductive, etc.). For example, when the AC load is a 220V resistive load, an AC solid-state relay with a voltage level of 220V can be selected; When the AC load is a 220V inductive load or a 380V resistive load, an AC solid-state relay with a voltage level of 380V can be selected; When the AC load is a 380V inductive load, an AC solid-state relay with a voltage level of 480V can be selected (this level of AC solid-state relay also has a higher static dv/dt index). At the same time, it is necessary to ensure good heat dissipation of solid-state relays, as their internal chips will experience certain power losses during operation, which will be dissipated in the form of heat. Poor heat dissipation may affect their operational reliability.