I have an application where I want to protect a triac from surges. How do I dimension a varistor for surge protection. I want to connect the varistor either in parallell with the triac or between line and zero. Ground is not available The triac operates at 230V (in another application at 400V) and can handle voltages up to 800V. Previously a varistor with a rated max energy of 84J (190J for the 400 V application) has been used but after a lot of problems with exploding varistors it have to be replaced. Of course I can not protect from a direct lightning strike but how much protection is recommended.
16 years ago