The NSE HT OVC (500 Joule) is a high temperature over voltage clamp. It is targeted at downhole wireline and drilling tools or other industrial applications where high temperature and large input variation in voltage may occur. This OVC is designed to clamp over voltage peaks that may occur if your tool suddenly looses its load, which will cause the topside voltage level to be moved to the downhole tool.

Example (Option code: B – cut off voltage = 600Vdc):
If topside power supply is providing 1000Vdc, and you have a voltage loss of 400Vdc over your wireline – you will have 600V on the tool head. If your motor/load for some reason momentarily disappears, the current will go to zero. This will in turn eliminate the voltage drop over the wireline, and you will get 1000V on your downhole electronics. This will occur (at least for some hundreds of milliseconds) even if you have a controlled topside power supply. With an over-voltage clamp, this energy will be absorbed, and the voltage on your electronics will remain at 600V even if you loose the load for a short moment.