I used to work in a factory where the electrical
installation was
basically undocumented. I was tought that to make sure to "power off"
the right section, I had to make a short circuit. To do this, 1) always
use proper insulated thick enough (in my case at least 2,5mm2) wire, 2)
Do not hesitate, but handle firmly, as to not allow "bad connections"
and 3) always look away when making the contact.
I've seen many people looking surprised when I did this, but I feel it's
indeed is a very secure way to make sure to switch off the right
section.
Bert
You did this with high voltage? Shorting out 480VAC by hand with a small
cable is a good way to shit your pants at the very least.