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Thread: AFCI required on MWBC?

  1. #171
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    Quote Originally Posted by LarryFine View Post
    Wayne, what is your point, as asked? That a MWBC that is used as 2 or 3 120v circuits is not required to have AFCI protection?
    My point would be that the the language of 210.12 is at the least ambiguous and confusing with respect to whether MWBCs require AFCI protection. Wayne seems to have taken up my point.

  2. #172
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    Quote Originally Posted by LarryFine View Post
    Wayne, what is your point, as asked? That a MWBC that is used as 2 or 3 120v circuits is not required to have AFCI protection?
    That would be the ultimate practical point yes, basically that the original argument that jaggedben presented does in fact hold.

    It's also interesting to parse the various definitions logically and see how well the NEC holds up as a consistent document, and see how well the implications match our preconceived notions.

    Cheers, Wayne

  3. #173
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    Quote Originally Posted by david luchini View Post
    And are you installing receptacle outlets on this "subcircuit" which is not a branch circuit?
    I'm assuming you are referring to the first sentence of 406.4, which reads "Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210."

    If we drop the "in accordance" part of that sentence, then the requirement is vacuously true for any electrical service with a main disconnect. As long as there is some OCPD, there will be some Branch Circuit on which the Receptacle Outlet is installed. The names we use for other subsets of the Premises Wiring System is immaterial.

    So the upshot of that first sentence of 406.4 is just to direct the reader to the requirements of Part II of Article 210 as far as Receptacle placement.

    Cheers, Wayne

  4. #174
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    Quote Originally Posted by wwhitney View Post
    So the upshot of that first sentence of 406.4 is just to direct the reader to the requirements of Part II of Article 210 as far as Receptacle placement.

    Cheers, Wayne
    Receptacle placement is covered in Article 210, well before Article 406. 406.4 doesn't say anything about receptacle placement. 406.4 provided a rule which you are trying to skirt.

    "Shall be installed in branch circuits" is a mandatory Code rule.

  5. #175
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    Quote Originally Posted by jap View Post
    . . . you smokin, drinkin, trolling,tail chasin,ambiguous whatever else you called me...
    "Who's scruffy-looking?!"
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #176
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    Quote Originally Posted by LarryFine View Post
    "Who's scruffy-looking?!"
    We all will be by the time we figure out exactly why we are required to install an AFCI, that we aren't convinced works most of the time, on a MWBC, that we're not sure how to define, just to pass an inspection given by an individual that probably doesn't put as much effort into confusing the issue as much as we do.

    Jap>

  7. #177
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    Quote Originally Posted by david luchini View Post
    "Shall be installed in branch circuits" is a mandatory Code rule.
    Sorry, can you be more specific? I can't find that text in 406.4.

    Anyway, a requirement of the form "Utilization Equipment type X shall be installed in Branch Circuits" is, as I say, satisfied in any installation by definition of Branch Circuit. The only question is whether the "voltage class" requirement applies to the Branch Circuit, or just a circuit supplying the Receptacle.

    Cheers, Wayne

  8. #178
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    Quote Originally Posted by jaggedben View Post
    A 'voltage class' is the voltages in a multi-voltage system! It gives examples right there in Article 100!
    I'm a little dubious, as the practice of defining a term in passing within another definition is a pretty poor one. If 'voltage class' is to be synomynous with 'Voltage, Nominal' it should be its own definition.

    On other hand, it is quite striking that the phrase 'voltage class' only appears in 3 places in Chapters 1-4.

    So if voltage class is different from Voltage rating, what is the upshot for interpreting the second sentence of 406.4(A)?

    Cheers, Wayne

  9. #179
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    OK, I tracked down a copy of ANSI C84.1-2006, which is referenced in the informational note for the definition "Voltage, Nominal" in Article 100, which has the only usage of the phrase "voltage class" prior to its use of 406.4(A).

    That document has the following section:

    3 System voltage classes
    3.1 low voltage (LV)
    : A class of nominal system voltages 1000 volts or less.
    3.2 medium voltage (MV): A class of nominal system voltages greater than 1000 volts and less than
    100 kV.
    3.3 high voltage (HV): A class of nominal system voltages equal to or greater than 100 kV and equal
    to or less than 230 kV.
    3.4 extra-high voltage (EHV): A class of nominal system voltages greater than 230 kV but less than
    1000 kV.
    3.5 ultra-high voltage (UHV): A class of nominal system voltages equal to or greater than 1000 kV.
    So if we take that as our guide, 406.4(A) is just telling us not to install a 125V receptacle on a system with nominal voltage greater than 1000 volts. :-)

    Or maybe the word 'class' in 406.4(A) is a just a bad choice of synonym for 'rating'.

    Cheers, Wayne

  10. #180
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    406.4 General Installation Requirements.
    Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210. General installation requirements shall be in accordance with 406.4(A) through (F
    There are many cases where a receptacle is not the "outlet" and is within a feeder. Receptacles supplying mobile homes, RV's and similar situations are not installed in the branch circuit are they? What about receptacle on a portable generator supplying a transfer switch/panelboard? Not the branch circuit either.

    I see that as meaning if the receptacle is the "outlet" then the rest of what is mentioned applies.

    Part III of 210 is "required outlets". There are many receptacles out there that are not covered by 210 part III in any way, some may even be part of a MWBC or even contain all the conductors of a multiwire circuit.
    I live for today, I'm just a day behind.

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