AFCI required on MWBC?

[david luchini]

I do not ignore 406.4. The portion of 406.4 that refers to voltage rating uses the term "circuit" instead of "Branch Circuit", just like 210.6 does, and 210.4(A) does. These sections are all consistent in this regard.

Cheers, Wayne

Is your mystery "subcircuit" (or is it small circuit or local circuit) a branch circuit?

 

[oldsparky52]

I gave a proof above that the Voltage rating is 240V per the NEC definitions. Which step do you disagree with? If none, please accept the result and put aside your preconceived notions.

Cheers, Wayne

There is no proof nor speculation to 210.4(C). ..

Let's just set aside my disagreement with you for one instant. Let's say you are correct and the circuit is a 240v circuit. What are you trying to accomplish? It sounds like you are trying to argue your way out of using AFCI protection. If that's not it, what is it?

 

[wwhitney]

The portion of 406.4 that refers to voltage rating uses the term "circuit" instead of "Branch Circuit", just like 210.6 does, and 210.4(A) does.

Correction, the relevant sentence in 406.4 uses the phrase "voltage class," not "voltage rating".

I did some searching through the 2014 NEC PDF, Chapters 1 through 4. The phrase "voltage class" only appears 3 times, in 100, definition of Voltage, Nominal; in 406.4; and in 480.2, definition of Nominal Voltage (Battery or Cell). Not sure what to make of the term, other than as an unusual synonym for "voltage rating".

I also searched the same Chapters for the term "voltage rating" which is far more common. Every time the term "voltage rating" was used in reference to a circuit, the word used for the circuit was just "circuit", not Branch Circuit. This is a consistent pattern.

Cheers, Wayne

 

[david luchini]

Correction, the relevant sentence in 406.4 uses the phrase "voltage class," not "voltage rating".

I did some searching through the 2014 NEC PDF, Chapters 1 through 4. The phrase "voltage class" only appears 3 times, in 100, definition of Voltage, Nominal; in 406.4; and in 480.2, definition of Nominal Voltage (Battery or Cell). Not sure what to make of the term, other than as an unusual synonym for "voltage rating".

I also searched the same Chapters for the term "voltage rating" which is far more common. Every time the term "voltage rating" was used in reference to a circuit, the word used for the circuit was just "circuit", not Branch Circuit. This is a consistent pattern.

Cheers, Wayne

So is your mystery "subcircuit" a branch circuit or not?

 

[wwhitney]

There is no proof nor speculation to 210.4(C)

210.4(C) says nothing about the Voltage rating of an MWBC. It only tells you what loads an MWBC may supply, absent one of the extra measures mentioned in the Exceptions.

The definition in Article 100 tells you the Voltage rating of a circuit depends on the potential difference(s) between the conductors of the circuit; how you connect the loads among those conductors is irrelevant.

Cheers, Wayne

 

[oldsparky52]

There is no proof nor speculation to 210.4(C). ..

Let's just set aside my disagreement with you for one instant. Let's say you are correct and the circuit is a 240v circuit. What are you trying to accomplish? It sounds like you are trying to argue your way out of using AFCI protection. If that's not it, what is it?

210.4(C) says nothing about the Voltage rating of an MWBC. It only tells you what loads an MWBC may supply, absent one of the extra measures mentioned in the Exceptions.

The definition in Article 100 tells you the Voltage rating of a circuit depends on the potential difference(s) between the conductors of the circuit; how you connect the loads among those conductors is irrelevant.

Cheers, Wayne

Hey, you skipped this part

What are you trying to accomplish? It sounds like you are trying to argue your way out of using AFCI protection. If that's not it, what is it?

 

[jaggedben]

Correction, the relevant sentence in 406.4 uses the phrase "voltage class," not "voltage rating".

I did some searching through the 2014 NEC PDF, Chapters 1 through 4. The phrase "voltage class" only appears 3 times, in 100, definition of Voltage, Nominal; in 406.4; and in 480.2, definition of Nominal Voltage (Battery or Cell). Not sure what to make of the term, other than as an unusual synonym for "voltage rating".
...

A 'voltage class' is the voltages in a multi-voltage system! It gives examples right there in Article 100!

Voltage, Nominal. A nominal value assigned to a circuit
or system for the purpose of conveniently designating its
voltage class (e.g., 120/240 volts, 480Y/277 volts, 600
volts).

(Emphasis added.)

 

[wwhitney]

Is your mystery "subcircuit" (or is it small circuit or local circuit) a branch circuit?

For the case of an MWBC on a single multi-pole breaker, this is the question that we've already discussed, is a proper subset of a Branch Circuit itself a Branch Circuit? I say no, based on the wording of the definition of Branch Circuit.

Cheers, Wayne

 

[david luchini]

I say no, based on the wording of the definition of Branch Circuit.

And are you installing receptacle outlets on this "subcircuit" which is not a branch circuit?

 

[LarryFine]

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?

 

[jaggedben]

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.

 

[wwhitney]

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

 

[wwhitney]

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

 

[david luchini]

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.

 

[LarryFine]

. . . you smokin, drinkin, trolling,tail chasin,ambiguous whatever else you called me...

"Who's scruffy-looking?!"

 

[jap]

"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>

 

[wwhitney]

"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

 

[wwhitney]

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

 

[wwhitney]

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

 

[kwired]

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.