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That's all well and good until the service neutral opens up.

Lol, Peter. that's a good point. Especially in my case, as the service drop is the original one serving a total of 5 apartment units. (With the original "A" base style meters.) I'll try to get some pictures of this mess to put up here, I can call it "Little Service of Horrors." [Linked Image]

Here's an interesting hypothetical thought: If the service neutral (ahead of all 5 services) were to open, would the load diversity of all the units minimize the possible imbalance?

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Seems to me that every argument against multiwire branch circuits stems from either the improper installation or improper modification of the circuit.

and:

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They are usually caused by some numbskull stuffing 6-#12 into a red wirenut or something like that.

Bingo! That seems to reflect most folks' negative experiences, but:

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I have NEVER run into a case of a problem caused because there wasn't a dedicated neutral run for each circuit.

In my business, that is the primary cause of trouble for both audio and control systems as I have mentioned in other threads. And in the case of multi-channel (circuit or load if you prefer) lighting systems like Panja, Vantage and Crestron as used in McMansions, the use of shared neutrals causes a lot of problems and in fact most of the manufacturers of that equipment will void warranty on equipment installed with multiwire feeds. As I do on any audio equipment not wired to the specifications I provide. Again, it all depends on the intended application.

I will probably shock a few by saying that I can see some applications where I personally would install multiwire, for example, circuits serving motor loads without VFD's; a lighting load consisting primarily of incandescent lighting; dedicated circuits for seasonal lighting......I'll probably think of a few more later.

As it stands, it really boils down to a cost vs. performance stance. In my case, the extra cost of the extra #12 white THHN (Around $50.00 for a 20-screen movie theatre) is more that repaid by the time and trouble saved in chasing out audio noise and erratic automation operation which I have encountered in installations without dedicated neutrals. Since a service call to a cinema is worth $65-$95 per hour with a four hour minimum, I would rather spend the extra up front (which by the way is factored into my installation bid)than have to do a gratis warranty service call. [Linked Image]

Stupid should be painful.