perryx5

I failed an inspection in the city of Atlanta the other day because I pulled some 12/3 MC cable to pick up some circuits I was adding in a small restaurant remodel. Inspector said that multiwire branch circuits required a neutral, or grounded conductor in this case, for each single pole circuit. He said that I would have to use 2 pole breakers on these circuits even though they were supplying receptacles. I have heard of this in residential wiring due to the ability for unskilled homeowners to get zapped by a neutral, but thought that there was an exception in commercial work due to qualified personnel maintaining the wiring. Checked the new code book, and no such exception exists anymore. Is anyone else enforcing this? Basically, in order to pull multiwire branch circuits, you either have to tie receptacle circuits together on a 2 or 3 pole breaker or pull a neutral for each circuit, eating up valuable conduit fill. Any opinions?

Thanks,
Jeremy

Minuteman

2 or 3 pole breakers would have nuisance trip issues, Install single pole breakers with handle ties.

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Chris Kennedy

Welcome to the Forum. You missed 210.4(B) if your under the 08.

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Chris Kennedy

Here.

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InPhase277

Pretty damned stupid rule, in my opinion. But yes, the inspector is right. Looks like the MWBC is a thing of the past. 2- and 3-pole breakers get expensive.

perryx5

Yeah, after failing, went to 210.4 and found no exceptions, had to agree that inspector was right, but he also said that handle ties were not a means of simultaneous trip since the trip mechanism in a molded case breaker operates independently of the handle. In other words, it has to be a 2 or 3 pole breaker. I will just start pulling a grounded conductor for every circuit. The extra #12 will still be cheaper than multipole breakers and I can pull 4 circuits per conduit to keep my derate at 70%. I will just run all 1/2" home runs and have to add a couple to each job, no big deal. (It's just money, it's not like we're in a recession or anything) I still could have sworn that in past NECs there was an exception to 210.4 for "qualified personnel".

perryx5

The MC cable manufacturers probably don't care for this rule either, because it renders 12/3 and 12/4 useless for anything other than 208 or 480 volt circuits that require a neutral (ovens, dryers, etc.).

480sparky

210.4(B) does not make MWBCs obsolete, even in commercial. More expensive, maybe.

But since you're in a restaurant situation, using MWBCs is very difficult when you provide GFI protection as required by 210.8(B)(1) with breakers.

The inspector is dead wrong in saying MWBCs require seperate grounded (neutral) conductors.

Your inspector needs to know the difference between a common-trip breaker and one with handle ties. They (the poles) are not only tied together externally (at the operating toggle), but internally as well. A common trip breaker will turn off all the poles of the breaker if only one trips.

A set of breakers with handle ties will not cause all the poles to turn off, but will turn them off all at once if you manually turn the breakers 'off'. Handle ties are one method of complying with 210.4(B).

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InPhase277

It's not any harder to pull another white wire in a pipe. Not to mention the inconvenience of having to turn off other circuits just to work on one.

Just to be on the safe side, the NEC ought to require no more than one circuit per pipe. And multiple circuits shouldn't enter the same box.

480sparky

I hope you're not serious about that.

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Minuteman

Say what???

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Dennis Alwon

Here is one problem with individual neutrals. If you have a pipe run and want to have 3 circuits all with their own neutral then you will have 6 ccc'c instead of 3 in the case of a MWBC. This creates extra heat in the conduit but is certainly legal as long as derating is taken into consideration.

I don't know about the bolt in type but the plug in style dp breakers don't cost much more than 2 single poles with ties.

Do they make 3 pole handle ties yet. I think I heard that one mfg. was making them but am not sure.

drsparky

I like the handle tie requirement; it makes it easier to lock out/tag out.
I would not consider a restaurant a place with qualified personnel. I may be off on this but I have always interpreted this to mean staff electricians. Having a burger flipper resetting breakers is not my idea of qualified.

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Bob Badger

What do qualified personnel have to do with the handle tie requirement?

drsparky

Read the OP.

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Dennis Alwon

The op thought there was an exception for qualified personal and handle ties but there is not

Bob Badger

Oh, now I got it.



Maybe I should read the entire thread before asking questions.

drsparky

My point was that I did not think that in any portion of the NEC that have exceptions for qualified maintenance personnel could ever apply to a commercial establishment such as a restaurant. 392.3(B) and 396.10 (B) are an example of an exception granted for qualified persons.

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Bob Badger

Are you serious or just stirring the pot?

Cause if your serious I want some of what your smoking.

Lets say I have to run nine 20 amp 125 volt branch circuits from a 208Y/120 panel to a location 75' away. I will use THHN or THWN-2 in EMT.

These are all liner loads so I would go with MWBCs (Multi Wire Branch Circuits)

So I would have

9 12 AWG Hots

3 12 AWG Neutrals

1 12 AWG EGC.

That is a total of 9 current carrying conductors which gets a 70% derating.

Still I could run all that in one 3/4" EMT and be 100% code compliant.

Now on the other hand if I used all two wire circuits ..

I would have

9 Hots

9 Neutrals

1 EGC.

Now I have 18 current carrying conductors and the derating hit is 50%.

12 AWG THHN is rated 30 amps in 310.16

30 amps x .5 = 15 amps, now those 12 AWG will need to have 15 amp breakers ........ customer wants 20 amp circuits.

Lets move up to 10 AWG THHN with its rating of 40 amps (T310.16)

40 x .5 = 20 amps so now we know we have to use at least 10 AWG or run more raceways.

So I would have

9 10 AWG Hots

9 10 AWG Neutrals

1 12 AWG EGC.

But wait, 250.122(B) requires the EGC to be also up sized.

So I would have

9 10 AWG Hots

9 10 AWG Neutrals

1 10 AWG EGC.


Now we have nineteen 10 AWG THHN conductors to install ......... that ain't fitting in a 3/4" EMT that will require 1.25" EMT .....much harder to run than .75" EMT.


With MWBCs

75' - 3/4" EMT

975' - 12 AWG THHN


With two wire circuits

75' - 1.25" EMT

1425' - 10 AWG.

Which one is 'easier'


We could also talk about how much less voltage drop there is with balanced MWBCs but just the material and labor savings is enough.

Chris Kennedy

Who are you, what have you done with Bob?

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