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Varistor selection?

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Hello,

I have a 120VAC circuit drawing 12KW. We need to control this load with a solid state relay (SSR).

I am looking at the Little fuse catalog as shown in the attachment below:

We are looking to use a 150A SSR module. Based on the attachment below we are looking to protect our SSR by connecting a MOV across its terminals by using the TMOV20RP200E part for our application. The problem is, I have never used varistors before and had a few questions:

1) The "continous Voltage" parameter is: 120 x 1.41 = aprx. 170VAC peak. Going by the Continous voltage column we see that this part is functional on 200 V peak. So is this correct?

2) The varistor voltage test at 1ma is between 281 and 344VAC. Does this mean that the varistor starts its conduction when the voltage spike attains anywhere between 281V and 344VAC?

3) The maximum clamping voltage seems to be when the voltage spike attains 530VAC which will allow the maximum conduction that the varistor can handle of 100A.... Is this correct?

4) I don't understand what the 8/20us in following column title means:

Maximum
Clamping
Voltage
8/20µs
???

All help and feedback appreciated?
r
 

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Energy rating of a Varistor is often defined using standardized transients such as 8/20 microseconds, where 8 microseconds is the transient's front time and 20 microseconds is the time to half value.
 
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