Hi wraper
Thanks, maybe I should fill in the gaps.
The UT61e already has MOVs in the design, there are not fitted to the cheap Chinese versions.
See attached picture, labelled SG1, 2, 3 & 4
One of my questions was asking if the MOVs I had chosen was right. Having just finished re-watching Dave's mm input protection video, it is now clear to me the answer is no.
I was wondering the significance of the turn on voltage verses the clamp voltage. I now have my answer.
Since the MOV turn on voltage will affect the DUT measurement, I need to choose MOVs with the turn on voltage for the max voltage I want to measure, the clamp voltage should not be too far off the turn on voltage.
Although Dave did not say in his video, I am guessing the input protection works by blowing the PTC and/or the ww resitor when the MOVs blow. So it is not a problem that the MOVs destory themselves, that is their job in the case of an extreme over voltage surge.
Thank wraper and masterTech for your explainations.