I made the mistake of paying a electrician for a job not quite finished.  It was an hourly agreement, so I can't say I've been ripped off, however it turns out he's not coming back so I'm trying to finish up. To give you a picture of the project, it is a barn with lighting, fans, and a few outlets.  Wires run through conduits, boxes and vapor proof T8 fixtures.

I have one neutral for lighting, fans and an outlet for a section of the barn.  Totaling the load for this area is almost 20 amps, the lighting feed is a 14 red wire. Fans are fed by a black 12 wire.

The fan load on that 12 wire is 10.5 amps, plus an outlet.  The lighting load on the 14 wire is 7 amps.  


Neutrals are all tied together and are a mixture of 12 and 14 wire.  The 14 wire comes from lighting and ties in with the 12 wire that runs from fan to fan.  A single 12 wire neutral goes to this entire section.

Can you have a multi-wire branch circuit that is 15 and 20 amps?  And can you have mix of 12 and 14 wire for the neutral?  It seems like this was the plan based on the mix of 12 and 14 wire.  Only other option I can see is that he ran 12 for the fans to avoid voltage drop and figured he didn't need to for the lighting.  We are as far as 100' from the panel.

Shortcutting fing electrician.....No excuse for that, particularly on a T&M job.

So are the fans on a 20 amp and the lights on a 15 amp breaker?

There are no breakers installed.  Wires drop where we planned a sub panel and a bank of switches. (though I'm rethinking the sub panel)

Any chance the 14 is used as switch legs only? Not code compliant but it's something I have seen old electricians do. I honestly wouldn't worry about it too much if this is the case. But if it's all in conduit I recommend you pull it out and repull 12.

If you want to do it right, pull a 12ga neut. to the fans and leave the 14 neut.  for the lights.  Put the hots to each on 20 and 15 amp breakers.
Put in the sub panel.  Pull at least 50 amps worth of wire to it.  More if you need for voltage drop/future need.

My gut reaction was this was wrong.  

Could one fix be to run a multi wire branch circuit at 15 amps?  Fans on one, lighting on the other.  seems like the 10.5 amp fan load is low enough for a 15 amp breaker.  Going this route, I'll have to run another circuit for the outlet, but I think that is more doable than ripping out all the existing neutrals.

That may work and would not meet any NEC.  
You sure you don't want to bring in a good sparky to fix this?

Bringing in another electrician is definitely an option.  I'm trying to get a full understanding of the situation first so I get it fixed right.

It's legit as long as the neutral conductor is sized to equal the highest amperage circuit breaker of the MWBC. In your case the #12 awg neutral was sized for the 20 amp leg of the MWBC.  Don't forget you'll need to use circuit breaker handle ties on any MWBCs. What your electrician was doing as I have done on rare limited occasions in the past and had inspected...does get discussed in numerous internet hits.... Here




On a side note; only because you're piped and single conductors who may utilize the raceway with "future" circuits, grouping (using wire ties or tape) of conductors is required @ the panel and in every pull/jct box that multiple MWBCs appear or pass through.

What year of the NEC requires grouping in all pull/jct boxes?

It sounds like he has a 12g neut to the panel for the MWBC, but then the 12g was spliced to a 14g.
And it would work, but does NEC allow that?  Might be OK on 15a breakers.

This diagram below is what I perceive the OP has. I had 2 similar examples that passed inspection. One was using an existing 12/3 MWBC in a kitchen remodel to extend the black leg with 12/2 to feed some additional counter receptacles and the red leg extended with 14/2 for recessed cans using a 20A and 15A breaker on the MWBC. Spoke with the Inspector beforehand about it and even brought it to his attention during the rough-in inspection.

The second was wanting to install a 10/3 MWBC for a 30A/120V 3wire camper receptacle and a 20A/120V circuit for some exterior premise convenience receptacles. Talked to a different area Inspector prior because I was concerned with the camper having an interior 110V loadcenter  and if that would instead redefine the MWBC as being a feeder. His answer was....because the camper is plug connected he considered it a MWBC, so the black leg is a 30A/1P and the red leg a 20A/1P made common with breaker handle ties.

The google search I posted above leads to other multi-internet discussions or examples about the circuity.

OP, if it looks boogered, do what DVCER suggests and use 2-15A/1P breakers then it won't matter what size neutrals went where.

ETA...Pull/jct box grouping is required for any style of circuit configuration whos conductors are looped or spliced (less excp.1 & 2) in the 2014 NEC 200.4(B) scroll down to Fig. 200-5 followed by the analysis.  

Off hand I think its the NEC 2008 which PA is still under but I think the pull/jct box segment is a common sense/safety requirement by my area's AHJ (Electrical Inspectors).  I've been doing so for years prior with raceways carrying mulit-ckt conductors, even grouping  conductors with individual dedicated neutrals. It does make it easier to tap off a specific branch circuit, then again, there's always the amp probe with if need be an artificially induced external load.

Thanks, I'm an electrician in Chicago so I don't have to worry about the NEC and is fear of MWBC's and all the other sillyness like AFCI's. I'm not a fan of tape or ty-wraps on conductors in pull boxes or panels.
I'll number tag my circuits and neutrals with all the circuit #'s, if an electrician can't figure out its a MWBC and know what to do with/about it maybe they should find a different line of work.

Jacassc, your drawing is spot on.  I had a sparky out today and he confirmed that it should be ok.  We did find issues where neutrals are tied together that shouldn't be.  Basically that 14 wire lighting neutral was tied to two different 12 wire neutrals.  . So we get to pull apart that work and redo it