ACCEPTED ANSWER
You're pretty close as is. You need to finish the first 2nd Stratum Mission which requires you to speak to Olympia on the 8th Floor at A1/A2 which is accessible without shutting off any currents. You also need to speak to Kujula on the 7th Floor at the camp site before you're able to turn in the mission. Once done with the mission, the currents can be shut off at B3 on the 6th Floor.
If you need help getting to that area of the 8th Floor, you need to go the long way around. The stairs at E5 on Floor 7 gets you to Floor 8 and you need to reach the stairs at C2 to return back to Floor 7. Once in that area of Floor 7, you need to head towards A4 which will allow you to reach the area you need to get to on Floor 8. So, in short:
Floor 7 - E5
Floor 8 - C2
Floor 7 - A4
Floor 8 - A1/A2