It can be easy or a nightmare depending how the power was run, labeled, how many j-boxes, home run cans, circuiting, size of property, other tenants, etc..
The challenge comes in when a lot of the electrical is hidden behind drywall, but the drywall is not being removed.
In a perfect case there would be home run can(s) with the circuit and panels labeled. Coming off that would be drops straight down the walls. Maybe a few j-boxes labeled here and there.
Nightmare it's run with MC cable horizontal thru walls, soffets, are other areas not set for demo work. The panels cold be anywhere in the building, not necessarily the closest. The circuits could come of multiple panels in several locations or different floors. Nothing labeled or even color correct for the voltage or circuit number. The same circuit powering different offices or even tenants is going thru demoed areas. You schedule late night work and somebody wants to stay late that night and work on their PC. Or adjacent offices work 24/7. The splices were done so poorly that something comes apart opening a box cover. Neutrals shared but not 1 splice was twisted before the nut. Something on the 277v lighting was done poorly and is ready to short and trip when the demo guys start shacking things up. Or live MC cables cut with the conductors turtled in the cable hanging in the ceiling. The trip on the substation is set to the minimum so low a 277 short could take out the entire floor, call center, IT room, fire controls, etc.. Even if a 120v circuit trips the property is so large it can take 30-60 minuets to find the breaker. Do you have your own access to the electrical rooms or do you have to find and ask for them to be open. Trying to find a few more available circuits in the existing panels. Panel schedules are outdated, such as labeled for a tenants long gone. It helps if someone knows the history of the building. They will still call something what it's former use was years later.
Some of the problems come for re-configuring the offices in the past. The property owner changes the size of the tenants office with a few doors or small walls, such as subdividing. But it was still wired as it was 1 tenants office. Other problems with maintenance work sub standard or companies doing a little electrical work that shouldn't like the office partisan wall electrical.
It's good to try and sort some things out before demo. Figure on 2 guys doing electrical demo, standing-by, laying out new home runes, or other work during the construction demo.
