Ok so back to BX, well BX has no grounding conductor to speak of, but it's a common practice to use the outer steel wrapped sheath as a ground path. Well we know that old BX has no grounding wire in it. A quick calculation will tell you that you can only pump about 13 amps through a 9 ohm resistance with 120 volts. I hope so. I have had to fix many situations exactly like what I just described.
Someone calls and says they smell something coming from their kitchen or wherever.
On one job in particular, the BX had gotten so hot that it burnt a hole right through the customer's kitchen ceiling, they didn't notice it because it was underneath the kitchen light fixture. On another job we removed a foyer light fixture to install a new one.