The NEC 3 story NM rule has been in effect for at least 30 yrs.
To be exact, this prohibition dates to the '75 NEC. I've been told that the campaign in favor of this rule was supported by an overwhelming barrage of photos depicting damage inflicted on the cable
during construction. That is the reason for this restriction-- not rats, or fire rating, or anything else.
right on the beach you'll find mc/bx that is nothing but rusted shards, but the boxes still are instact to great extent.
This won't happen with Al-armored MC, a product with which I've had much experience. What
is wrong with it is lack of mechanical strength. Get an overzealous sheetrocker and the stuff just unravels. You can practically get it to break by sneezing on it. This doesn't happen with steel BX.
