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?
Best Answer
Typically the connection of 12/3 to two side by side breakers (black on one, red on other) is used to run a 220v line. A 220v line has two hots - each carrying 110v - pulled from adjacent breakers on the panel. In such cases, the single white line is the 220v Neutral.
Speaking electrically : What this guy did was use 12/3 to carry 220v to a junction box where he divided it back up into 110 - which should be fine because in reality the 12/3 is two parallel 110v lines, with a single neutral. The single neutral isn't really a problem here - ultimately all lines share a single neutral back at the breaker box. In your case, the shared neutral stops at a junction box - and the lines to the outlets are on their own neutral lines.
Are there any hazards to the receptacles? No, as long as they're wired properly its no different than connecting the neutrals back at the neutral bus bar.
Speaking in terms of CODE and what's allowable - I honestly don't know if it's legal or not, but I cannot think of a reason why it wouldn't be. The junction boxes are accessible, and using 12/3 to carry 220v is legit, and each outlet is wired to 110 properly.