You could measure a lot of things when messing with power lines, but ultimately someone has to be responsible that circus that are powered of or safe for any re

You could measure a lot of things when messing with power lines, but ultimately someone has to be responsible that circus that are powered of or safe for any reason stay safe. You measurements cannot give that guarantee, but installations have procedures that ensure this. Everything deviating from that procedure, which normally includes setting a switch with a safety pin and attached note about the work carried out, will lead to accidental powering up at some point or another. Again: when dealing with high voltage circuits make absolutely certain that the person or machine controlling the circuit is informed (or it's you personally who shut off the power and no one else can turn it on). If you are trained to work on live circuits, please ignore my advice. You'll know better :-)