Guys I build a timer for electronics equipment's.I need to add a varistor protection to this. Varistor is connected between live wire & Earth line.Is it ok?
Only connecting Line to earth can cause problems. I have used three MOVs such that each of the three terminals (Line, Neutral, and Earth) are all bridged by MOVs. If you only want to use one MOV, then debe mentions, put the MOV from Line to Neutral so that the fault current returns via Neutral.
I once read an article that showed that high voltage spikes in some (it was implied all) computer power supplies are clamped by the input rectifiers and bulk storage capacitor such that the power supply protects the MOVs. How humorous .
Not good or safe, a high voltage spike big enough could make the case live, your mov could go accross the mains to protect your device.
Using 3 as dick has is ok, in fact it adds protection from the easth going live.