Exposed BX cable

What is your opinion or the requirement regarding Armored Cable (BX) exposed outside of a wall at the interior of a home? Is it required that it be “in wall” or in an approved conduit? Can it be exposed? I see it often and always call it out as being improper. Just wanted other thoughts.

It is permitted by the NEC to be run exposed unless subject to physical damage, which is a completely subjective requirement. IMO unless there’s a chance of being easily damaged then it’s fine if run exposed. The NEC specifically permits AC cable to be run on the underside of floor joists if stapled to every joist.

what about inside a basement in a residential home? would this be considered a damp or wet location? I want to run AC cable from an existing junction box fed by conduit on the ceiling to tun another service/fixture. can i use exposed ac cable?
if this is permitted, can i clamp the ac cable outside the ceiling / finished drywall?

I doubt the basement would meet the NEC definition of Location, wet. If it does you have other issues like serious waterproofing deficiencies.

If the basement were conditioned I don’t think it would be a damp location either. This is a case by case basis. The NEC says “moderate degrees of moisture”. What that is depends on the person judging the install.