I punched through some conduit one time while I was drilling anchors in some concrete, it blew a breaker and arced pretty good, but other than that I was fine.

That’s why it’s important to make sure that your tool is properly grounded or double-insulated.

If I would have drilled into those cables, I'd probably rather have offed myself than to deal with the aftermath.

Germans. The basement walls are made from prefab concrete slabs with junction boxes and flex hose for the cables already in there.

Thin ceiling slabs with steel rebar sticking out are lowered onto these. That's when the elec-chickens drill some holes and put in their cables, mostly in flex hose. Then the ceiling/floor proper is poured. That's how I remember it from my active time.

Figure something similar is going on here. That's why the cables for the basement wiring are partly in concrete. I expected everything to be in flex-hose because that's what I could see in the junction boxes but here we are.

Not very repair friendly, depending on where damage occurs.

If all goes well, this was the most delicate and messy part of it. The hole is already large enough to accommodate all the cables from the inverter to the power switching box which is going to sit next to the main fuse box. The next holes I'm sure I can just drill. No cables in the wall there. It's going to be covered up with cable ducting and maybe some gypsum at the edges.

Hope to get this done before Christmas.