Mom needed a receptacle on her balcony. I drilled through the wall with a 16 inch bit in my hammer drill. Problem: wall is 18 in. thick, brick veneer and two layers of concrete with an empty (?) middle part. As best I could I projected a spot inside for a mating hole and drilled. Then tried two more. I couldn’t see daylight. I figured there must be some opaque insulation in between those two layers of concrete. After much poking I managed to get a stiff wire from the inside to the outside and pulled a 3 conductor wire and telephone cord (with modular jack) through the holes. The major problem was the hollow middle wasn’t as wide as the concrete parts so, in the end, it was sheer luck that I managed to bend that wire enough to find the outside whole from one of the inside ones.