Current carring conductors

[jclint07]

120 volt, 20 amp MWBC (wired with 12/3 with ground Romex) supplied from 120/240V single phase system= Neutral is not CCC.

120 volt, 20 amp SINGLE BC supplying power to (2) switch legs for the ceiling fan (wired with 12/3 with ground Romex). One switch for 5 amp motor AND one switch for 5 amp light kit. Neutral is a CCC.

Sound right?

 

[roger]

120 volt, 20 amp MWBC (wired with 12/3 with ground Romex) supplied from 120/240V single phase system= Neutral is not CCC.

120 volt, 20 amp SINGLE BC supplying power to (2) switch legs for the ceiling fan (wired with 12/3 with ground Romex). One switch for 5 amp motor AND one switch for 5 amp light kit. Neutral is a CCC.

Sound right?

See post 20.

Roger

 

[infinity]

120 volt, 20 amp MWBC (wired with 12/3 with ground Romex) supplied from 120/240V single phase system= Neutral is not CCC.

120 volt, 20 amp SINGLE BC supplying power to (2) switch legs for the ceiling fan (wired with 12/3 with ground Romex). One switch for 5 amp motor AND one switch for 5 amp light kit. Neutral is a CCC.

Sound right?

Yup see post #9.

 

[roger]

I used shorthand, but what it is referring to is called "load diversity." It is now dealt with in annex B. Basically, it is recognition in the code that, if the wires in the conduit are not carrying full load at the same time then the heat generation is less and the number of "current carrying conductors can be increased."

Regarding the code reference year, it could have been 12 years ago, for all I know, because I don't remember the last time I looked and I am getting old. There use to be a fine print note, that made a statement something about a load diversity of 50% calculated "under engineering supervision" cauld be used to increase the number of current carrying conductors.

Sorry for the confusion.

Huhhhh?
:blink:

Roger

 

[roger]

Yup see post #9.

Now I see what he was saying and I agree.

Roger

 

[jclint07]

Wow, my head is spinning.

Post 9 is exactly what I was referring to in my post. Was reading too fast & overlooked.

 

[mak134]

Who is right?

Who is right?

No disrespect to the inspectors but, why would it matter what their opinion may be, it is spelled out in the NEC and the laws of physics, you would follow that.

In a two wire circuit both conductors carry the same current, In a single phase MWBC the neutral only carries the imbalance and would not be a CCC. In a three wire MWBC of a wye system, the neutral would carry the same as the ungrounded conductors and would be a CCC. In a four wire MWBC of a wye system the neutral would carry the imbalance and would not be a CCC.

The above is not taking any additive harmonics into consideration which is pretty much overblown anyways.

Roger

I'm in Chicago so forget the romex. Roger seems to be saying that four separate circuits with separate neutrals in a shared conduit equals 4 ccc. Rob answered it equals 8 which by code would require that the conductors be derated to 70%. Which is it?

 

[infinity]

I'm in Chicago so forget the romex. Roger seems to be saying that four separate circuits with separate neutrals in a shared conduit equals 4 ccc. Rob answered it equals 8 which by code would require that the conductors be derated to 70%. Which is it?

I'm not sure that Roger said it was 4 CCC's but in your example the answer is 8 CCC's.

 

[realolman]

I'm in Chicago so forget the romex. Roger seems to be saying that four separate circuits with separate neutrals in a shared conduit equals 4 ccc. Rob answered it equals 8 which by code would require that the conductors be derated to 70%. Which is it?

I should look to be sure, but it seems to me with #12 awg it doesn't matter until it gets to be 9 CCC

 

[Dennis Alwon]

I should look to be sure, but it seems to me with #12 awg it doesn't matter until it gets to be 9 CCC

This is true more than 9CCC-- meaning 10 or more and assuming 90C wiring and no other derating factors

 

[roger]

I'm in Chicago so forget the romex.

The wiring method doesn't matter

Roger seems to be saying that four separate circuits with separate neutrals in a shared conduit equals 4 ccc.

I don't know how you interpreted what I said to mean four CCC's, I said, "In a two wire circuit both conductors carry the same current"

Roger

 

[jeremysterling]

No disrespect to the inspectors but, why would it matter what their opinion may be, it is spelled out in the NEC and the laws of physics, you would follow that.

In a two wire circuit both conductors carry the same current, In a single phase MWBC the neutral only carries the imbalance and would not be a CCC. In a three wire MWBC of a wye system, the neutral would carry the same as the ungrounded conductors and would be a CCC. In a four wire MWBC of a wye system the neutral would carry the imbalance and would not be a CCC.

The above is not taking any additive harmonics into consideration which is pretty much overblown anyways.

Roger

I believe you, but I need the argument.

The Art. 100 definition FPN says, "Electronic equipment, electronic/electric discharge lighting, adjustable-speed drive systems, and similar equipment may be non-linear loads."

"May" is subjective, so let's say these loads are, in fact, non-linear. Since even toasters have a circuit board, it is electronic equipment. (Because some minds are thinking this way)

315(B)(4)(c) refers to a major portion of the load being non-linear. Is that 51%? Or does this mean any non-linear load is a problematic consideration. (Because some minds are thinking a 200% neutral with K-factor transformer?)

Sorry, I'm over-exaggerating, but the code seems too offer inspectors an easy argument to compel counting the neutral as a CCC.

So, short of an engineering degree, how can I underblow the consideration of additive harmonics.

 

[roger]

how can I underblow the consideration of additive harmonics.

Easy, how many service calls have you had to repair damaged wiring or equipment due to additive harmonics?

Roger

 

[don_resqcapt19]

...

315(B)(4)(c) refers to a major portion of the load being non-linear. Is that 51%? Or does this mean any non-linear load is a problematic consideration. (Because some minds are thinking a 200% neutral with K-factor transformer?) ...

Yes, major portion does mean that the non-linear load must be over half of the total load.

 

[jeremysterling]

Easy, how many service calls have you had to repair damaged wiring or equipment due to additive harmonics?

Roger

To be honest, I haven't had many service calls to repair damaged wiring or equipment due to under-deration of CCC's by table 310.15(B)(2)(a)!

 

[roger]

To be honest, I haven't had many service calls to repair damaged wiring or equipment due to under-deration of CCC's by table 310.15(B)(2)(a)!

And nor have I or most electricians I know of.

Roger

 

[don_resqcapt19]

I used shorthand, but what it is referring to is called "load diversity." It is now dealt with in annex B. Basically, it is recognition in the code that, if the wires in the conduit are not carrying full load at the same time then the heat generation is less and the number of "current carrying conductors can be increased."
...

The diversity tables are in Annex B because no one really knows what that term means. Those tables were in the actual code for one code cycle and moved to the Annex when in the the next code cycle they could not come to an agreement as to what load diversity means and how you would calculate.

 

[mbeatty]

Edited for brevity.

Since even toasters have a circuit board, it is electronic equipment. (Because some minds are thinking this way)

I now want to find an electronic toaster and check it out. I've bought 2 toasters in 31 years of married life and did not know electronic ones existed. Learn something new, everyday. :slaphead:

 

[donf]

Why buy a toaster

Why buy a toaster

Stop!

Do not purchase a toaster. With the extra money (vapor) in your tax return, simply open a Federally Insured account at a bank of your choice.

 

[kwired]

310.15 B 4 says that a neutral conductor that carries only the unbalanced current from other conductors of the same circuit need not be counted? if this is not a branch circuit with a neutral then what is it? For example if we pull four 20 amp circuits each with their own neutral is that 4 ccc's or 8? It makes a big difference when you get to the derating. Any inspectors out there have an opinion? I assume that since this is in the code there must be a situation where the neutral is not considered a ccc otherwise the code would just say that it is a ccc 100% of the time.

Bold is the answer to the OP question. Any other time it is current carrying for the purpose of determining number of current carrying conductors in a raceway or cable.

I should look to be sure, but it seems to me with #12 awg it doesn't matter until it gets to be 9 CCC

More than 9 usually is the point at which you will end up having to increase conductor size. There is still adjustments for 4-6 and 7-9, and after considering ambient temperature you still could end up needing to increase conductor size.

Edited for brevity.

I now want to find an electronic toaster and check it out. I've bought 2 toasters in 31 years of married life and did not know electronic ones existed. Learn something new, everyday. :slaphead:

Unless there is a solid state control for the heating elements the amount of harmonics will be fairly minimal- maybe a solid state timer or clock unless you have a toaster with internet browsing capabilities, or the ability to control other appliances in the house.