Kindly advise 215.2 (A) (1)

david luchini

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But where does 215.2(A)(1) say the second sentence applies to 110.14(C) determination? The subject of the first sentence is ampacity. The subject of the second sentence is size. 110.14(C) requirements are regarding ampacity... and says nothing regarding size.
110.14(C) is a general requirement for all electrical installations under the code. Why would you think it doesn't apply?

The second sentence of 215.2(A)(1) does address the minimum size of a conductor, BUT that minimum size is determined by allowable AMPACITY. The determination of ampacity must comply with the temperature limitations in 110.14(C).
 

Smart $

Esteemed Member
Location
Ohio
It may usually work out...but lets make a couple of changes to the original post and apply your method.

Lets go with 300A non-continuous and 320A continuous load, and the same 0.92 correction factor. This would give us...

1) 75?C rated terminations, minimum copper conductor size for 620A is 2 sets of 350kcmil at 310A each.

2) 125% ? 320A + 300A = 700A. 90?C-rated copper conductor minimum size is 2 sets of 350kcmil at 350A each.

3) 620A ? 0.92 = 674A. 90?C-rated copper conductor minimum size is 2 sets of 350kcmil at 350A each.

4) 700A OCPD. 240.4(B) applies. Adjusted and corrected ampacity can be as low as 601A. 601 ? 0.92 = 653A. 90?C-rated copper conductor minimum size is 350kcmil parallel at a combined pre-adjusted/corrected ampacity of 350A each.

The 90?C-rated copper conductor satisfying all four requirements is 2 sets of 350kcmil. But the 75?C rated terminations will overheat with the continuous load. The 125% factor for the continuous load should have the effect of oversizing the terminations so that they can handle the extra heat from the continuous loading.

In the example above, however, we would allow the 350kcmil lugs, negating the effects of adding in the 25% of continuous load.
I disagree. Yes, they will be heated... but not overheated. When the noncontinuous and continuous loads are energized simultaneously, the current in the [insulated wire] conductor will be 620A. The 75?C ampacity of parallel 350kcmil copper is 620A. The conductor temperature (we are led to believe) will be 75?C... which is not exceeding the 75?C terminal temperature rating. You handpicked a borderline case... now live with it!!!

Not sure what you are saying in your last sentence.
 

Smart $

Esteemed Member
Location
Ohio
110.14(C) is a general requirement for all electrical installations under the code. Why would you think it doesn't apply?
Apply to what? I think 110.14(C) applies to all that it applies to. You question appears to be too ambiguous. Can you elaborate or be more specific?

The second sentence of 215.2(A)(1) does address the minimum size of a conductor, BUT that minimum size is determined by allowable AMPACITY. The determination of ampacity must comply with the temperature limitations in 110.14(C).
And just exactly what is allowable ampacity. Where does 110.14(C) use the term allowable ampacity...??? How does allowable ampacity relate to ampacity as used in 110.14(C)? How is allowable ampacity used in the second sentence of 215.2(A)(1) different than ampacity as used in the first sentence? Why isn't it all combined into one sentence if it is the same ampacity?

Anyway, are we to Round 15 yet? I'm getting tired of dancing around the ring!
 
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david luchini

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I disagree. Yes, they will be heated... but not overheated. When the noncontinuous and continuous loads are energized simultaneously, the current in the [insulated wire] conductor will be 620A. The 75?C ampacity of parallel 350kcmil copper is 620A. The conductor temperature (we are led to believe) will be 75?C... which is not exceeding the 75?C terminal temperature rating!!!

Not sure what you are saying in your last sentence.
I must disagree with what you are saying here. To follow your logic, why would we need to add the 25% at all for continuous loads?

Take for example a 100A non-continuous load with #3 THWN and 75?C terminations. We are led to believe that the conductor temperature will be 75?C. Now lets take that same 100A load and make it continuous. The load is still only 100A, but the code would make us increase the conductor size to #1 THWN. Why? If the 100A load would still only make my #3 THWN conductor temperature reach 75?C, even when the load is continuous, why must I increase my conductor size?
 

Smart $

Esteemed Member
Location
Ohio
I must disagree with what you are saying here. To follow your logic, why would we need to add the 25% at all for continuous loads?

Take for example a 100A non-continuous load with #3 THWN and 75?C terminations. We are led to believe that the conductor temperature will be 75?C. Now lets take that same 100A load and make it continuous. The load is still only 100A, but the code would make us increase the conductor size to #1 THWN. Why? If the 100A load would still only make my #3 THWN conductor temperature reach 75?C, even when the load is continuous, why must I increase my conductor size?
Because the Code says so...!!!

Now where does it say anything about continuous and noncontinuous loads in 110.14(C)?
 

david luchini

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Apply to what? I think 110.14(C) applies to all that it applies to. You question appears to be too ambiguous. Can you elaborate or be more specific?
Applies to determining allowable ampacity per 215.2(A)(1).

But where does 215.2(A)(1) say the second sentence applies to 110.14(C) determination?
And just exactly what is allowable ampacity. Where does 110.14(C) use the term allowable ampacity...??? How does allowable ampacity relate to ampacity as used in 110.14(C)?
Allowable ampacity is given in the Tables in Art. 310. You will notice that for the same conductor size, allowable ampacities are different for different temperature rated conductors.

110.14(C) tells us that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor or device. If we have a 75?C rated termination or device, we must select the ampacity of the conductor based not to exceed the 75?C allowable ampacity from Art. 310. If the non-continuous load plus 125% of the continuous load per 215.2(A)(1) gives us an allowable ampacity of not less than 750A, then that would be 2 sets of 500mcm or 3 sets of 250mcm, or 4 sets of 3/0awg, or 5 sets of 1/0awg.
 

Smart $

Esteemed Member
Location
Ohio
I must disagree with what you are saying here. To follow your logic, why would we need to add the 25% at all for continuous loads?

Take for example a 100A non-continuous load with #3 THWN and 75?C terminations. We are led to believe that the conductor temperature will be 75?C. Now lets take that same 100A load and make it continuous. The load is still only 100A, but the code would make us increase the conductor size to #1 THWN. Why? If the 100A load would still only make my #3 THWN conductor temperature reach 75?C, even when the load is continuous, why must I increase my conductor size?
Another viewpoint is why is the requirement for noncontinuous plus 125% continuous before the application of any adjustment or correction factors. If we are really padding the ampacity of the conductors for continuous loads, wouldn't we do so after adjustment and correction???
 

Smart $

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Location
Ohio
Applies to determining allowable ampacity per 215.2(A)(1).
But why not just ampacity, as used in the first sentence? Why must it be allowable ampacity, as used in the second sentence?

Allowable ampacity is given in the Tables in Art. 310. You will notice that for the same conductor size, allowable ampacities are different for different temperature rated conductors.
And ampacity is determined under Article 310, not Article 215.

110.14(C) tells us that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor or device. If we have a 75?C rated termination or device, we must select the ampacity of the conductor based not to exceed the 75?C allowable ampacity from Art. 310.
Absolutely correct.

If the non-continuous load plus 125% of the continuous load per 215.2(A)(1) gives us an allowable ampacity of not less than 750A, then that would be 2 sets of 500mcm...
Yes allowable ampacity... but not ampacity.

[Actual] minimum ampacity is 650A, while [minimum] allowable ampacity is 750A.

Does 110.14(C) use the term allowable ampacity??? Let me answer that... It does not!!!
 
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david luchini

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Because the Code says so...!!!

Now where does it say anything about continuous and noncontinuous loads in 110.14(C)?
It doesn't! Nor does it need to!!!!!! 215.2(A)(1) covers that.

Once more into the breach...110.14(C) tell you that the temperature rating ASSOCIATED WITH THE AMPACITY of a conductor shall be SELECTED AND COORDINATED so as NOT TO EXCEED the lowest temperature rating of any connected termination, conductor or device.

Selecting a 90?C temperature rating associated with the ampacity of 760A for two sets of 400mcm to meet the required minimum allowable ampacity of 750A (for the non-continuous load plus 125% of the continuous load) WOULD EXCEED the lowest temperature rating of any connected termination (75?C.)

110.14(C) tell you NOT TO EXCEED...in your example, you HAVE EXCEEDED (90?C exceeds 75?C.)
 

david luchini

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But why not just ampacity, as used in the first sentence? Why must it be allowable ampacity, as used in the second sentence?
Because they are not the same thing. The allowable ampacity is given, for example, in Table 310.15(B)(16). For instance, a 95A continuous load would need a minimum conductor size (215.2(A)(1)), before any adjustment or correction factor, with an allowable ampacity of 119A. From Table 310.15(B)(16), this would be a #1 AWG THWN minimum conductor. Suppose the #1 AWG THWN was installed in an ambient of 32?C. The ampacity for that #1 AWG would be 122A. That ampacity is large enough for the load. Both parts of 215.2(A)(1) are satisified.


And ampacity is determined under Article 310, not Article 215.
Yes, that is exactly what I said.

Allowable ampacity is given in the Tables in Art. 310. You will notice that for the same conductor size, allowable ampacities are different for different temperature rated conductors.

Yes allowable ampacity... but not ampacity.
Yes, the allowable ampacity. As given in Table 310.15(B)(16) (for this case.) Based on a temperature of 75?C, (ie, not to exceed the lowest temperature rating of any conductor, termination or device.)
 

Smart $

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Location
Ohio
It doesn't! Nor does it need to!!!!!! 215.2(A)(1) covers that.

Once more into the breach...110.14(C) tell you that the temperature rating ASSOCIATED WITH THE AMPACITY of a conductor shall be SELECTED AND COORDINATED so as NOT TO EXCEED the lowest temperature rating of any connected termination, conductor or device.

Selecting a 90?C temperature rating associated with the ampacity of 760A for two sets of 400mcm to meet the required minimum allowable ampacity of 750A (for the non-continuous load plus 125% of the continuous load) WOULD EXCEED the lowest temperature rating of any connected termination (75?C.)

110.14(C) tell you NOT TO EXCEED...in your example, you HAVE EXCEEDED (90?C exceeds 75?C.)
But 400kcmil copper conductors have a 75?C allowable ampacity of 670A, which is not less than the minimum required ampacity of 650A. This complies with 110.14(C) and 215.2(A)(1) first sentence. The conductors I choose to use are 90?C-rated conductors, as permitted by 110.14(C), so I can make ampacity adjustment, correction, or both... and comply with 215.2(A)(1) second sentence.
Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
 
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david luchini

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But 400kcmil copper conductors have a 75?C allowable ampacity of 670A, which does not exceed the minimum required ampacity of 650A.
This statement is the problem. 215.2(A)(1) says that the conductors shall have an allowable ampacity of not less than 750A. 670A is less than 750A.


This complies with 110.14(C). The conductors I choose to use are 90?C-rated conductors, as permitted by 110.14(C), so I can make ampacity adjustment, correction, or both...
110.14(C) permits you to use 90?C-rated conductors, BUT it tells you that ampacity of the conductors cannot exceed the 75?C ampacity for the given conductor size (unless the equipment is rated and listed for the 90?C-rated conductors.)
 

Smart $

Esteemed Member
Location
Ohio
This statement is the problem. 215.2(A)(1) says that the conductors shall have an allowable ampacity of not less than 750A. 670A is less than 750A.
(2) 400kcmil copper, 90?C-rated conductors have an allowable ampacity of 760A, before adjustment and correction, which is greater than the 750A allowable ampacity requirement of 215.2(A)(1) second sentence.


110.14(C) permits you to use 90?C-rated conductors, BUT it tells you that ampacity of the conductors cannot exceed the 75?C ampacity for the given conductor size (unless the equipment is rated and listed for the 90?C-rated conductors.)
As I keep saying, 110.14(C) says ampacity, not allowable ampacity.

The ampacity of (2) 400kcmil 75?C-rated copper conductors is 670A. When I apply adjustment and correction to my 400kcmil 90?C-rated copper conductors, I get 760A ? 0.92 = 699A. Because 699A > 670A, my conductor ampacity is limited to 670A.
 

Smart $

Esteemed Member
Location
Ohio
...

The ampacity of (2) 400kcmil 75?C-rated copper conductors is 670A. When I apply adjustment and correction to my 400kcmil 90?C-rated copper conductors, I get 760A ? 0.92 = 699A. Because 699A > 670A, my conductor ampacity is limited to 670A.
Getting back to the OP'ers exercise, and my post thereafter, Step 4 concludes that conductors with a 670A ampacity (paralleled 400kcmil copper) are not protected with the 800A ocpd. I suppose I should have noted my Steps only check for compliance. They do not demonstrate determination of final conductor ampacity.
 

m sleem

Senior Member
Location
Cairo
Please check this example:

Continous load is 400A
Non-continous load is 250A

thus:
1-min ampacity (before correction) will be 750A

2-min ampacity (after correction) will be 600A, where: correction factor is 0.92
So, next higher size will be 700A

3-OCPD will be 800A

We shall select between 1&2, which one is higher

So, the designed cable ampacity will be 750A, where 240.4(B) is applicable.
I did mistake it should be 650A/0.92 = 706.5A
 

david luchini

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As I keep saying, 110.14(C) says ampacity, not allowable ampacity.
It seems pretty clear that "allowable ampacity" is measure of ampacity. The "Allowable Ampacity" tables in Art. 310 tell you the ampacities of the given conductors under the listed conditions (and before any correction or adjustment factors are applied.) The fine print notes for the tables tell you that the allowable ampacities result from consideration of "temperature compatibility with connected equipment, especially the connection points."

110.14(C) tells you that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected equipment. 110.14(C)(1)(b)(2) tell you that for equipment over 100A, you can use conductors with higher than 75?C temperature ratings, provided the ampacity of such conductors does not exceed the 75?C ampacity of the conductor size used.

(2) 400kcmil copper, 90?C-rated conductors have an allowable ampacity of 760A, before adjustment and correction, which is greater than the 750A allowable ampacity requirement of 215.2(A)(1) second sentence.
But the temperature rating (90?C) associated with the 760A ampacity of (2) 400kcmil EXCEEDS the lowest temperature rating of any connected termination (75?C). This is a direct violation of 110.14(C).
 

Smart $

Esteemed Member
Location
Ohio
It seems pretty clear that "allowable ampacity" is measure of ampacity. The "Allowable Ampacity" tables in Art. 310 tell you the ampacities of the given conductors under the listed conditions (and before any correction or adjustment factors are applied.) The fine print notes for the tables tell you that the allowable ampacities result from consideration of "temperature compatibility with connected equipment, especially the connection points."

110.14(C) tells you that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected equipment. 110.14(C)(1)(b)(2) tell you that for equipment over 100A, you can use conductors with higher than 75?C temperature ratings, provided the ampacity of such conductors does not exceed the 75?C ampacity of the conductor size used.



But the temperature rating (90?C) associated with the 760A ampacity of (2) 400kcmil EXCEEDS the lowest temperature rating of any connected termination (75?C). This is a direct violation of 110.14(C).
Well I see we keep going round and round with the same explanations... as such we're not getting anywhere. I do understand your point of view. I cannot say you are absolutely wrong in your interpretation. Yet I feel you are not being open minded either...

Perhaps you can entertain my viewpoint and explain to me how you implement...
.
1) Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(6)... [110.14(C)(1) sencond sentence],

2) The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the
continuous load...
[215.2(A)(1) second sentence], and

3) Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both... [110.14(C) general statement].​

.
Please provide an example.

In the meantime, I will consider how to rewrite my "steps" to show you compliance with the issue you are contending.
 
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david luchini

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Yet I feel you are not being open minded either...
I can, at times, be quite open minded. Yet I cannot open my mind enough to allow me to knowingly violate a Code requirement. :p

Perhaps you can entertain my viewpoint and explain to me how you implement...
............1) Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination
............provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(6)... [110.14(C)(1) sencond sentence],
I'm not sure what I would be implementing here (110.14(C)(1) second sentence.) This sentence simply directs you to the Ampacity Table 310.15(B)(16) unless the equipment is listed or marked otherwise. This sentence cannot be divorced, however, from the first sentence of 110.14(C)(1) which tell you to use part (a) for equipment rated 100A or less, or marked for 14 AWG through 1 AWG conductors, and to use part (b) for equipment rated over 100A or marked for conductors larger than 1 AWG. The example in the original post is dealing with equipment over 100A, so we would use 110.14(C)(1)(b). As such we would use EITHER a 75?C rated conductor (eg, THWN) OR a 90?C rated conductor (eg, THWN-2) PROVIDED ampacity of such conductors does not exceed the 75?C ampacity of the conductor size used. Applying this to the previous example, 2 sets of 400mcm Cu (THWN-2) would have an ampacity of 670A, not 760A.

............2) The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the
............noncontinuous load plus 125 percent of the continuous load... [215.2(A)(1) second sentence], and
I think this is fairly clear. From the original example, Noncontinuous load (250A) plus 125% of the continuous load (400A*1.25) = 750A. The smallest feeder conductor size shall have an allowable ampacity without any adjustment of correction factors of not less than 750A. As the terminations for the circuit are rated 75?C, 110.14(C) requires me to use the ampacity based on the 75?C rating, even if I am using a 90?C rated conductor. The smallest conductor that gives me an ampacity (from Table 310.15(B)(16)) that is not less than 750A is 2 sets of 500mcm Cu (380A*2 = 760A.)

............3) Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both... [110.14(C) general
............statement].
Having established our minimum conductor size as 2 sets of 500mcm Cu (maybe someday I'll stop using mcm and start using kcmil...) we need to address the first sentence in 215.2(A)(1). Our load current is 650A. If there are no correction factors (for ambient temperature) or adjustment factors (for number of ccc's in the raceway) then we already know that our feeder ampacity (760A) is large enough to supply the load (650A.) Let's imagine that the feeder was sharing a raceway with another feeder so that there were 6 ccc's, and I was planning to use 500mcm THWN because I had it readily available. The adjusted ampacity of 2 sets of 500mcm THWN would be 608A. This is clearly too small to supply the 650A load. I could look at using 2 sets of 600mcm THWN which would give me an adjusted ampacity of 672A...large enough to supply the load. OR using general statement from 110.14(C), I could look at using 2 sets of 500mcm THWN-2. 110.14(C) permits me to use the higher temperature rating for ampacity adjustment, so...430A*2*0.8=688A. This is also large enough to supply the load. Either 2 sets of 600mcm THWN or 2 sets of 500mcm THWN-2 would be acceptable for this example.

Here is another example of selecting the conductors applying both 215.2 and 110.14(C) together...

http://www.mikeholt.com/news/archive/html/master/conductor.htm



 

Smart $

Esteemed Member
Location
Ohio
Sorry for the delayed response. I go to Today's Posts when I access the forum, and with a bunch of new posts you latest post must have got pushed to page 2. I hardly ever get to page 2, so I didn't notice you had posted until I did a search for new posts that I had replied to...

I can, at times, be quite open minded.
Key words ;)

Yet I cannot open my mind enough to allow me to knowingly violate a Code requirement. :p
Nor would I want you to. FWIW, I respect your sticking to your beliefs. :thumbsup:

I'm not sure what I would be implementing here (.) This sentence simply directs you to the Ampacity Table 310.15(B)(16) unless the equipment is listed or marked otherwise. This sentence cannot be divorced, however, from the first sentence of 110.14(C)(1) which tell you to use part (a) for equipment rated 100A or less, or marked for 14 AWG through 1 AWG conductors, and to use part (b) for equipment rated over 100A or marked for conductors larger than 1 AWG.
The point was that 110.14(C)(1) second sentence specifically says to base determination on Table 310.15(B)(16) as appropriately modified by 310.15(B)(6). It does not say to do so by way of 215.2(A)(1) [or 210.19(A)(1), but will continue to refer to both as 215.2 for this discussion].

In other words I'm questioning where the code says to use noncontinuous load plus 125% continuous load for the purpose of 110.14(C) determination. You previously answered this question "Why would I not?" I do not recognize that as a legitimate answer.

I see two parts to 215.2(A)(1):
Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220.
...and...
The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
The first part requires the ampacity (which I assume to be the final derated ampacity) to be not less than the calculated load. There is no extra 25% inclusion for continuous loads.

The second part requires the allowable ampacity, before the application of any adjustment or correction factors, to be not less than an extra 25% for continuous loads.

110.14(C) uses the term ampacity, which is used in the first part of 215.2(A)(1). 110.14(C) does not use the term allowable ampacity, which in 215.2(A)(1) is only used in the second part.

If we are basing 110.14(C) determination on Table 310.15(B)(16) by way of 215.2(A)(1), what makes the second part predominant over the first part???


The example in the original post is dealing with equipment over 100A, so we would use 110.14(C)(1)(b). As such we would use EITHER a 75?C rated conductor (eg, THWN) OR a 90?C rated conductor (eg, THWN-2) PROVIDED ampacity of such conductors does not exceed the 75?C ampacity of the conductor size used. Applying this to the previous example, 2 sets of 400mcm Cu (THWN-2) would have an ampacity of 670A, not 760A.[/QUOTE]
As I stated before, the step where I used 2 sets of 400kcmil at their 760A combined ampacity rating was for verifying compliance with 215.2(A)(1), which has no stipulation that 110.14(C) requirements must be combined in this verification. If you have any gripe whatsoever with my steps, based on what you are trying to point out, it would be with my first step verifying compliance with 110.14(C).

I think this is fairly clear. From the original example, Noncontinuous load (250A) plus 125% of the continuous load (400A*1.25) = 750A. The smallest feeder conductor size shall have an allowable ampacity without any adjustment of correction factors of not less than 750A. As the terminations for the circuit are rated 75?C, 110.14(C) requires me to use the ampacity based on the 75?C rating, even if I am using a 90?C rated conductor. The smallest conductor that gives me an ampacity (from Table 310.15(B)(16)) that is not less than 750A is 2 sets of 500mcm Cu (380A*2 = 760A.)
This just takes us back to the questioning the predominance of 215.2(A)(1) second sentence over first sentence. Where is it stipulated???

Having established our minimum conductor size as 2 sets of 500mcm Cu (maybe someday I'll stop using mcm and start using kcmil...) we need to address the first sentence in 215.2(A)(1). Our load current is 650A. If there are no correction factors (for ambient temperature) or adjustment factors (for number of ccc's in the raceway) then we already know that our feeder ampacity (760A) is large enough to supply the load (650A.) Let's imagine that the feeder was sharing a raceway with another feeder so that there were 6 ccc's, and I was planning to use 500mcm THWN because I had it readily available. The adjusted ampacity of 2 sets of 500mcm THWN would be 608A. This is clearly too small to supply the 650A load. I could look at using 2 sets of 600mcm THWN which would give me an adjusted ampacity of 672A...large enough to supply the load. OR using general statement from 110.14(C), I could look at using 2 sets of 500mcm THWN-2. 110.14(C) permits me to use the higher temperature rating for ampacity adjustment, so...430A*2*0.8=688A. This is also large enough to supply the load. Either 2 sets of 600mcm THWN or 2 sets of 500mcm THWN-2 would be acceptable for this example.
I'm agreeable to the result(s) you've established here, but I notice you use the calculated load of 650A as a basis of determination. Why use it here and not for 110.14(C)???

Here is another example of selecting the conductors applying both 215.2 and 110.14(C) together...

http://www.mikeholt.com/news/archive/html/master/conductor.htm
FWIW, I've searched the internet for articles relating to this matter. The ones that deal with continuous loading do follow the method you are using. I've not found any that support my method conclusively. However, I found a bevy of articles that to my mind seem to completely avoid the issue... :D


 
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