No, the 08 code does not ban them, it adds a couple of requirements to make them easier to identify along with tied breaker handles.

I agree with you, multiwire circuits are proffessional. If they are running separate neutrals for each line they must run into pipe fill and de rating issues a lot. Remember, a shared neutral does not need to be counted as a current carrying conductor for de rating purposes, individual neutrals do.

Whenever I see pipe where shared neutrals could have been used but weren't it is an indication to me that the installer was not an electrician. Others may have a different view, but to myself and thousands of proffessionals, multiwire circuits are standard practice.

i'd like to meet the man who can afford to use all that extra material :) those electricians dont sound too much like electricians at all do they. the 08 nec will in no way ban mwbc's, only require common trip to keep people who don't know how to properly work on electrical systems (such as your classmate) from getting shocked. that seems like it would be working backwards if you ask me, as the neutral would carry much more current that way. but many "electricians" do seem to mess them up when piped. i can't tell you how many times i've found 3 circuits sharing a neutral with all circuits on the same phase. kinda scary, and dangerous since there is no overload protection for the neutral conductor. but handle ties will fix that problem

All I can say is I totally agree with the other replies here, and that those guys sound like bozos.

"You sure never see them in the commercial world"???
"Thank god 08 code is banning all multiwire branch circuits"???
"One guy got shocked and will never touch one again???"
............You HAVE to be KIDDING me???

In commercial, the 277 volt lighting (can and often) uses MWBC. That is one of the economies of that system. One neutral for 3 lighting circuits.

A major reason NOT to use them is that dimmers and related home automation systems get bent over the shared neutral. I'd never use them to feed residential lighting circuits.

I hate it when teachers/professors use their position to cast their personal feelings onto unsuspecting students. The OP here sounds like he is a thinker as well as a learner. Good for him. The electrical text books I have read all go into detail about the benefits of MWC. They also go into detail about the pitfalls and dangers...such as an open in the neutral and why it's imperitive to pigtail the neutrals in the circuit. I don't do this for a living, but I can sure see the cost and labor benefits to a well designed circuit.

I do mostly residential remodel and rewire work and MWBCs are a great time and money saver in those applications. Most often I use them in kitchens and room additions. I also always use a DP breaker, regardless of the "same strap" rule.

What is going to limit their use in the '08 NEC is the (supposed) expanded requirement for arc-fault breakers.

What is going to limit their use in the '08 NEC is the (supposed) expanded requirement for arc-fault breakers

I don't really expect 2 pole AFCIs to be any more expensive than 2 single pole devices. Up to this point Cutler Hammer has supplied code compliant 2 pole AFCIs, GFCIs, and AFCI /5MA GFCI combo breakers. I don't expect this will change with the new requirements.

I'd offer that guys that don't use MWBCs in commercial and industrial settings just plain don't understand issues with voltage drop. And, they darn sure aren't bidding competitively in most cases -IMNSHO anyway

OK, what does voltage drop have to do with a multi-wire circuit?

"OK, what does voltage drop have to do with a multi-wire circuit?"

A MWBC "acts" like a 240v circuit, the more the (2 or 3) circuits are balanced the better.
We all know 240v circuits are MUCH less prone to voltage drop.

I sure hope that's sarcasm petey, you're confusing the poor boy.

Yea, and it's cheaper to run something on 240V. :)

For a given wattage, the voltage drop at 240 volts is half that compared to supplying the same wattage at 120 volts. When all is said and done, the voltage drop for a given wattage load at 240 volts is 25% of the drop at 120 volts, expressed as a percentage of the voltage supply. Much more efficient.

Well he asked, didn't he Ron?

Sounds like a bozo.
He probably has problems with 3 phase circuits also (the ultimate multi wire circuit).
I hope the is a community college type class.
He would get eaten alive by the engineering students at a four year school.

I agree MWBC'S are fine to run.I pretty much never get to run them though ,I have plans to follow(industrial/commercial) and it seems every engineer i work with makes sure that all circuits have a seperate neutral.

"every engineer i work with makes sure that all circuits have a seperate neutral."

Hire some better engineers.

lol,not my decision,i just do my job according to code and contract .