In 2001, some electricians added two circuits to my house in California. I took a close look at their wiring and had some questions.
At the Service Panel, there are two 20-amp circuit breakers on the left side of the panel. Both breakers are connected to the same 12/3 Romex cable, with the red wire attached to one breaker and a black wire attached to a second breaker. The two breakers are not tied together.
The 12/3 cable feeds into the a junction box in the crawlspace where it connects to two 12/2 Romex cables. The red wire on the 12/3 cable attaches to a black wire on one 12/2 cable which provides power to my living room, and the black wire is connected to the black wire on a second 12/2 cable which provides power to a bedroom. Thus, the two 12/2 share a neutral.
This wiring configuration is confusing. Is this a "Shared neutral" situation? I am pretty sure that this was inspected in 2001, but is this configuration allowed by modern code? Was this allowed in 2001? What are the hazards of this sort of configuration? Does this present a hazard to the receptacles in the living room and bedroom?