Minimum discharge time recommended at the end of cable testing [Archive]

gchoquette

February 11, 2021, 01:53 PM

What is the minimum discharge time recommended at the end of cable testing?

I faintly remember 10 minutes, but I think this is incorrect. I believe that you are supposed to use a grounding stick and discharge the cable that way.

Please correct me if I am wrong.

michaellabeit

February 11, 2021, 04:21 PM

What is the minimum discharge time recommended at the end of cable testing?

If I remember correctly, DC and AC tests charge cables differently so the discharging time will depend on the type of test conducted. Megger states (https://www.instrumart.com/assets/Megger-insulationtester.pdf) the following with regard to DC insulation resistance testing: "It is very important that capacitance be discharged, both before and after an insulation resistance test. It should be discharged for a period about four times as long as test voltage was applied in a previous test." In their DC hipot testing slides NETA states the same thing: discharging should last 4 times the test interval.

However, if you're conducting AC hipot testing, either at 50/60 Hz or VLF the discharging shouldn't take nearly as long.