Hi
What is inside of following device inside? Is it just varistors (MOV)?

And is this circuit do same job?
Thanks

 

It could be a varistor or a gas discharge tube. It might also be a tiny spark gap.

 

The allied projects show a circuit breaker on over-voltage, surges, lightning strikes etc

 

The allied projects show a circuit breaker on over-voltage, surges, lightning strikes etc

Certainly Max is right!! Every gas-tube over voltage device I have seen always included a circuit breaker because the protection device does not reset after it is triggered. That is because they are very non-linear, which is very common.