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Rules to follow when using varistor

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1. Working environment of varistor:

Should be within the scope of the technical conditions:

Ambient temperature: -40C ~ +85 °C;

Relative humidity: up to 96% at +40±2°C;

Atmospheric pressure: up to 8.5KPa.


2. Selection of varistor voltage

Select according to the power supply voltage. Taking full account of the fluctuation range of the operating voltage of the grid (or circuit), when selecting the varistor voltage value of the varistor, leave enough margin. The general domestic fluctuation range is 30%. It is also necessary to consider the supply voltage continuously applied across the varistor and cannot exceed the "continuous operating voltage" value listed in the specification sheet. For 220V ~ 240V AC power supply lightning arrester, varistor with a varistor voltage of 470V ~ 620V should be used. Selecting a varistor with a higher varistor voltage can reduce the failure rate and prolong the service life, but the residual voltage is slightly increased.


3. Selection of traffic flow

The nominal discharge current of the varistor should be greater than the surge current required or the surge current that may occur each year. The nominal discharge current should be calculated from the value of the impact of the surge resistance life cycle of the pressure sensitive resistor for more than 10 times, which is about 30% of the impact flow (ie 0.3 IP).


4. Selection of clamp voltage

The clamp voltage of the varistor must be less than the voltage that the protected component or device can withstand, ie the safe voltage.


5. Parallel connection of varistor

When a varistor does not meet the requirements of the nominal discharge current, multiple varistor should be used in parallel. Sometimes in order to lower the limiting voltage, multiple varistors are used in parallel even if the nominal discharge current meets the requirements. It is important to note that when the varistor is used in parallel, it is necessary to strictly select the parameters with the same parameters (for example: ΔU1mA≤3V, Δα≤3) for pairing to ensure uniform distribution of current.


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