Hello all... New York City here. I have to use BX... code. I have 2-wire( there is no ground in BX by the way in 2-wire) ran from the breaker. It is for my bathroom. The house was built in 1938 or 1939. The entire top floor (2 bedrooms and 1 bath) is all run on ONE breaker!!
That is how they did it back then I guess. I want to run lights to the ceiling, lights over the vanity, and a fan over the tub/shower... on 3 different switches.
My question is: Do I need to run 3-wire or can I pull it off (on a 20 amp) on 2-wire? If so,
How do I connect them all together? I guess you can tell I am a ham-and-egger. Take it easy on this DIY-er please!! I'm a plumber Jim... not a magician... lol Thanks All :)

The outer sheath is the ground. There is a BX connector which is used to connect the BX to the box and a BX plastic bushing the goes inside of the cut BX cable so the sheath doesn't cut the wires.

12 AWG - no more than 20 A, 15 or 20 A breaker
14 AWG - no more than 15 A, 15 A breaker

I = Power(watts)/V; V = 120

Bath should have a 20 Amp GFCI circuit.

Not sure if I answered the question.

All I'll say is be careful. You must have a license to do electrical work in NYC, and I'm almost positive this applies to your own home as well.

Good luck.

Oh, and I forgot. They DID relax the "no NM cable" rule in NYC for homes. "BX" or conduit is not mandatory any more.
Check your local building codes and NEC amendments. NYC has it's own set of rules.