OK, I can't take it anymore. I really thought this was a no-brainer. First of all:
There is nothing wrong whatsoever with using multiwire branch circuits. I prefer to see them in commercial applications only but they are certainly allowed in residential. If you don't know what a multiwire branch circuit is (MWBC), it is when 2 or more current carrying conductors share the same neutral, providing the conductors are from different phases. In residential that would be limited to a double pole circuit breaker but we can use a 3 pole breaker for a commercial application with 3 phase power available. There are ways to use handle ties on single pole breakers for both 240 and 3 phase.
MWBCs are great because you don't have to pull as many neutral wires which saves space in conduit, allowing the use of smaller conduit, takes up less space and terminals in boxes and panels and uses no more load on a neutral than if you only had one circuit, and even help with voltage drop. They are great in a commercial environment where only qualified people install or maintain the electrical equipment but can be a nightmare if unqualified people don't know what they are doing.
Here are the downsides to a MWBC:
1) Unqualified, inexperienced people working on MWBC or those that don't know an MWBC exists.
2) Lifting the neutral (ungrounded conductor) from the neutral bar can cause some serious problems depending on how the circuits are wired.
3) If not properly installed, they can cause some serious problems and damage to equipment or life safety issues. All receptacles must be in parallel and never have a neutral in series feeding through a receptacle. This is why a kitchen counter for example would have to utilize a 2-pole GFCI or every single receptacle would have to be a GFCI receptacle because you cannot daisy chain like you would normally.
So, with all of that being said, NEC 210.4 (B) states that "Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates."
Therefore, in the case of the above installation stating that the junction box serves an MWBC that are circuits 2, 15 & 41 in panel "C" makes it impossible to comply with NEC 210.4(B) because panels are manufactured with the left side being odd numbers from top to bottom and the right side being even numbers from top to bottom. Each of the 3 circuits in question are on different areas of the panel not next to each other, therefore unable to be on a 3 pole breaker or even 3 single pole breakers with handle ties installed.
Also verified was that the breakers are on 3 different phases, which they are. Circuit 2 is on A phase, 15 is on B phase and 41 is on C phase.
Upon further inspection a spare neutral and ungrounded conductor were found in the same JB that comes from the same panel C so the best course of action will be to use the spare ungrounded black conductor to pull another white grounded conductor, therefore providing all 3 circuits with their own neutral, eliminated the MWBC. Of course the neutrals will have to be separated and grouped with their ungrounded conductors in the panel and the JB as per NEC 210.4(D) and 200.4(B)
