The following image shows a junction box that I opened up in an 80+ year old house. This house has various generations of wire types, from BX, to fabric covered NM (very old and newer old), plastic NM, etc.
Power is supplied via the large fabric covered cable on the right and leaves leave via the black Romex cable on the left. Prior to taking the photo, I removed a very old (white turned almost completely brown) ceramic pull chain fixture. I also removed the oily, peeling electrical tape from one of the splices to see how it was made.
Check out this beauty:
2 - The splices were made by stripping some insulation from the outgoing Romex, wrapping it around the source wire and then taping the splice. No solder, no wire nuts.
3 - No cable clamp was used for the outgoing Romex. Instead, the ground wire was wrapped around the cable and the hole in the box, "securing" the Romex to the box.4 - You can't tell from the photo, but based on the color of the fabric on the source cable, the hot and neutral are reversed. The reason I opened this box is because I was working on a light switch down stream of this junction box. When I opened the switch box I noticed that the white was switched and the black wires were twisted and taped. Again, no wire nut and no cable clamps.
Having already been in the panel, I knew that a black wire was attached to the breaker, so there must be another junction box in between the panel and the box I was working on. The color swap had to have happened somewhere, so I went looking upstream.
What I found was that there was a junction box up in a joist bay, inside what used to be a cold air return. That box has a BX cable, the large fabric covered cable and a plastic coated Romex attached. It is also 8 feet into the bay and covered in decades old dirt and grime. The only way for me to access it would be to pull down part of the basement "ceiling", something I did not have the time nor the desire to do. I'm not even 100% sure if that is where the hot/neutral switch was made. That is going to be a job for another day.
My temporary solution was to mark the fabric wires in the box I was working in, swap the outgoing wires so that the black wire would be hot in the switch box, secure the box to the joist with screws, install a cable clamp and use wire nuts. I then closed up the box and hung a tag noting that the hot & neutral were swapped somewhere upstream. (Tag not shown)