Feeder calc. w/cont. & derating

[websparky]

Bob,

Let's see if I have this correct.

1.) A 200A load is supplied by a feeder that has 4 current carrying conductors.
2.) Table 310.15(B)(2)(a) says 80% adjustment for 310.16.
3.) 4/0 @ 80% = 208A.
4.) Problem solved.

 

[bob]

Bob,

Let's see if I have this correct.

1.) A 200A load is supplied by a feeder that has 4 current carrying conductors.
2.) Table 310.15(B)(2)(a) says 80% adjustment for 310.16.
3.) 4/0 @ 80% = 208A.
4.) Problem solved.

If the 200 amp load is 125% cont + 100% non-cont then 80% of the
90C rating 4/0 = 260 x 0.80 = 208 amps. 310.15.B(4)(a) says that if the neutral carrys only the unbalanced load the neutral is not counted when applying Table 310.15(B)(2)(a). If thats the case you could use 3/0.

 

[winnie]

As I understand the original poster's questions, the core point of this discussion is the meaning of the phrase "before the application of any adjustment or correction factors" in 215.2(A)(1).

The issue of 4 current carrying conductors is just a side issue, brought in to cause an adjustment factor; perhaps the example of _two_ single phase feeders in the same conduit (with 4 current carrying conductors and normal neutrals) would make a better example. The point is that we have to apply adjustment factors to the conductor ampacity.

As the OP was describing things, feeders are required to have an ampacity of 100% non-continuous plus 125% continuous loading _prior_ to such adjustment, but after any such adjustment, such feeders are only required to have an ampacity of 100% non-continuous plus _100%_ of continuous.

I believe that this is a correct analysis of 215.2(A)(1), but that the requirements of 215.3 may force a conductor ampacity larger than that required by 215.2(A)(1). 215.3 does not say anything about the adjustment factors applied to the conductors; it simply requires OCPD of 100% non-continuous + 125% continuous. Depending upon the application of the 'rounding up' rule, this will require adjustment of conductor size so that the OCPD properly protects the conductors.

-Jon

 

[Bob NH]

I'm going to try this based on similarity to Example D3(a) in Appendix D of the 2005 Code (page 70-719).

The OCPD must be greater than or equal to 100% of non-continuous load plus125% of the continuous load, so OCPD must be at least 200 Amps.

But the actual current in the ungrounded conductors (based on the example) must be checked against the ampacity in the raceway, and the ampacity for termination. Furthermore, they must be protected by the OCPD.

So the 90 degree ampacity from Table 310.16 for selection of the conductors must be 180 Amps/0.8 = 225 Amps. AWG 3/0 Copper is required.

The 75 degree ampacity to protect breaker terminations is 200 Amps, which is equal to 100% of noncontinuous + 125% of continuous load, so 3/0 meets that requirement.

Since the actual required current of 180 Amps exceeds the 175 Amp standard circuit breaker, it is permitted by 240.6(A) that the conductor be protected by a 200 amp breaker.

So the code-permitted result is 3/0 copper conductors with a 200 Amp breaker.

 

[bob]

The point is that we have to apply adjustment factors to the conductor ampacity.

As the OP was describing things, feeders are required to have an ampacity of 100% non-continuous plus 125% continuous loading _prior_ to such adjustment, but after any such adjustment, such feeders are only required to have an ampacity of 100% non-continuous plus _100%_ of continuous.
-Jon

The statement "but after any such adjustment, such feeders are only required to have an ampacity of 100% non-continuous plus _100%_ of continuous." is meaningless.
You determine the Minimum Ampacity based on the 100% non-continuous plus _125%_ of continuous load. Pick a conductor. Then you make the adjustments to the ampacity of the conductor based on the 90C ampacity if it is rated at 90C. After the adjustments the conductor still must meet the Minimum Ampacity at 75C. You do not apply the 125% again. It is already in the minimum requirements. Assume you have caculated a minimum ampacity that requires a conductor of 200 amps. 3/0 at 75C has an ampacity of 200 amps. After applying the adjustments for the number of conductors and temperature if required, the new ampacity of 3/0 will likely not meet the Minimum Ampacity previously calculated. If so you need to increase the conductor size til it does meet the minimum requirements. As posted in the previous post the extra 25% is added so that the conductor will act as a heat sink for the breaker plus breakers will only carry 80% of its rating for continuous load.

 

[Bob NH]

The requirement that OCPDs be sized for 125% of continuous loads drives the wire sizing which must be protected by the oversized breaker.

Are there any continuous load panels and breakers that would allow sizing of breakers and conductors to supply the continuous loads at 100% rating without requiring increased copper?

 

[bob]

The requirement that OCPDs be sized for 125% of continuous loads drives the wire sizing which must be protected by the oversized breaker.

Are there any continuous load panels and breakers that would allow sizing of breakers and conductors to supply the continuous loads at 100% rating without requiring increased copper?

Bob
Yes there are. However I do not know what the minimum size breaker
would be. Look at 210.19(A)1 exception 1. I allows the 25% addition
to be ignored for these type breakers. Perhaps a Google search would provide
the answer to the minimum breaker size.

 

[winnie]

The statement "but after any such adjustment, such feeders are only required to have an ampacity of 100% non-continuous plus _100%_ of continuous." is meaningless.
You determine the Minimum Ampacity based on the 100% non-continuous plus _125%_ of continuous load. Pick a conductor. Then you make the adjustments to the ampacity of the conductor based on the 90C ampacity if it is rated at 90C. After the adjustments the conductor still must meet the Minimum Ampacity at 75C. You do not apply the 125% again. It is already in the minimum requirements.

This is _exactly_ the issue being discussed. You have just asserted one of the possible readings of the code, but without supporting this interpretation.

NEC 215.2(A)(1):
[BGeneral.[/B] Feeder conductors shall have an ampacity no less than required to supply the load as computed in Parts II, III, and IV of Article 220. The minimum feeder-circuit conductor size, before the application an any adjustment or correction factors, shal have an allowable ampacity not less than the noncintinuous load plus 125 percent of the continuous load.

As I read this:
Conductors are required to have an ampacity not less than the load served. I read this to mean 100% non-continuous plus 100% continuous.

Next, the conductor is required to have an ampacity before the application of any adjustment or correction factors of 100% non-continuous plus 125% continuous. This makes it clear that in the most common use of the conductors, the requirement is 100% non-continuous plus 125% continuous.

As I read this, the 100% requirement _always_ applies, but the 100% plus 125% requirement only applies to the most common situation, when no adjustment factors apply.

In the present example, the OP gave us 100A non-continuous + 80A continuous loading, but also an adjustment factor of 0.8. This 0.8 adjustment factor applies to the 90C ampacity.

As I read 215.2(A)(1) this tells us that the minimum conductor ampacity is 180A, and that additionally the minimum conductor ampacity before any adjustment is 200A. The minimum conductor ampacity is determined at 75C, the terminal rating of the attached devices. After any adjustment factors are applied, an ampacity of 180A is sufficient to meet the requirements of 215.2(A)(1). This adjusted ampacity may be determined from the 90C conductor rating.

(Note: As I've stated above 215.3 and 240.4 and 240.6 also play into conductor sizing.)

-Jon

 

[bob]

Feeder conductors shall have an ampacity no less than required to supply the load as computed in Parts II, III, and IV of Article 220. The minimum feeder-circuit conductor size, before the application an any adjustment or correction factors, shal have an allowable ampacity not less than the noncintinuous load plus 125 percent of the continuous load.

As I read this:
Conductors are required to have an ampacity not less than the load served. I read this to mean 100% non-continuous plus 100% continuous.

That is incorrect. When ever you have a continous load the ampacity of the overcurent device is 125% of the cont + 100% of the non-cont per 210.20(A).
210.20(B) refers to 240.5 which requires that the conductors be protected
against overcurrent in accordance to the ampacities in table 310.15.
No exclusions except as noted in the exceptions.

Next, the conductor is required to have an ampacity before the application of any adjustment or correction factors of 100% non-continuous plus 125% continuous. This makes it clear that in the most common use of the conductors, the requirement is 100% non-continuous plus 125% continuous.

The article says the Minimum Capacity before the application of any adjustment. That is a big difference. I do not see why this is unclear. You have a dictate that says how to caculate the Minimum Ampacity.
You can not have a conductor ampacity less that the minimum.

As I read this, the 100% requirement _always_ applies, but the 100% plus 125% requirement only applies to the most common situation, when no adjustment factors apply.

That is incorrect. That requirement applys in every installation that has continous load per 210.20(A) as stated above.

In the present example, the OP gave us 100A non-continuous + 80A continuous loading, but also an adjustment factor of 0.8. This 0.8 adjustment factor applies to the 90C ampacity.

As I read 215.2(A)(1) this tells us that the minimum conductor ampacity is 180A, and that additionally the minimum conductor ampacity before any adjustment is 200A.

The minimum ampacity is 200 amps. 100 amps + 1.25 x 80 = 200 amps.

The minimum conductor ampacity is determined at 75C, the terminal rating of the attached devices. After any adjustment factors are applied, an ampacity of 180A is sufficient to meet the requirements of 215.2(A)(1). This adjusted ampacity may be determined from the 90C conductor rating.

How can you have a new minimum ampacity just because you applied an
adjustment factor. You still have the same 200 amps. Because of the adjustment factor being applied to the ampacity to the chosen conductor,
the conductor now has 20% less ampacity. You must choose a larger conductor.

 

[LarryFine]

Ambiguity in the NEC? Whoda thunkit?

 

[hardworkingstiff]

When ever you have a continous load the ampacity of the conductor is 125% of the cont + 100% of the non-cont per 210.20(A).

When I read 210.20(A), I do not see "conductor" written anywhere in the paragraph. What I see is the rating of the overcurrent device needs to be rated for 100% of the noncontinuous and 125% of the continuous loads.

 

[websparky]

Hard,
You must read in context!

210.20 Overcurrent Protection. Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

 

[bob]

When I read 210.20(A), I do not see "conductor" written anywhere in the paragraph. What I see is the rating of the overcurrent device needs to be rated for 100% of the noncontinuous and 125% of the continuous loads.

Stiff
You are correct. I went back and corrected my error.

 

[winnie]

That is incorrect. When ever you have a continous load the ampacity of the conductor is 125% of the cont + 100% of the non-cont per 210.20(A).
No exclusions except as noted in the exceptions.

I disagree. 210.20(A) discusses the requirements for OCPD, not the requirements for conductors. The requirements for the OCPD are as you describe, but these requirements are _different_ from those applied to the conductors.

210.19 discusses the ampacity of the conductors.

The current discussion is of feeders (article 215), however the language of the relevant sections is essentially the same.

The article says the Minimum Capacity before the application of any adjustment. That is a big difference. I do not see why this is unclear. You have a dictate that says how to caculate the Minimum Ampacity.
You can not have a conductor ampacity less that the minimum.

Ahh. Now we have the core of the argument, and this is a very good point.

215.2(A)(1) has _two_ sentences. My point (as well as my interpretation of the original poster's point) is that these two sentences represent two separate requirements.

If I read what you are saying correctly, the second sentence simply describes the requirements of the first sentence. I disagree, however it is a very good point.

How can you have a new minimum ampacity just because you applied an
adjustment factor. You still have the same 200 amps. Because of the adjustment factor being applied to the ampacity to the chosen conductor,
the conductor now has 20% less ampacity. You must choose a larger conductor.

This is exactly the point. You read 215.2(A)(1) as having a single requirement, 100% + 125% continuous. I interpret 215.2(A)(1) as giving us _two_ requirements, _both_ of which need to be met. One requirement applies in _all_ cases; the other requirement only applies prior to the application of adjustment factors.

The first requirement is simply 100% non-continuous plus 100% continuous. The second requirement is 100% non-continuous plus 125% continuous, however this second requirement applies only to the conductors prior to the application of any adjustment or correction factors.

As I have mentioned several times in my previous posts, there are additional requirements on conductor ampacity, including that inferred from 215.3, which sets OCPD requirements, and the fact that the OCPD must protect the conductors. All of these _separate_ requirements must be met, however some of these requirements only apply in limited situations.

-Jon

 

[bob]

Winne
I am giving you a chance to convince me you are correct. How about using 210.20 and 210.19 to determine the size breaker and conductor size for the following:
1. 100a N-cont + 75 A Cont 30C
2. 100a N-cont + 75 A Cont 42C
3. 100a N-cont + 75 A Cont 42C and 4 current carring conductors in conduit.

Bob

 

[winnie]

Bob,

That sounds reasonable. I will figure for your examples above, and show my reasoning. I may then add a couple of additional examples.

-Jon

 

[winnie]

For the below I will assume 90C conductors and 75C terminations. I presume that the OCPD are not being subject to increased operating temperature, which would otherwise open up a whole other kettle of fish.

The steps that I will follow are:
1) Use article 310 to find the minimum suitable conductor that meets the requirements of 210.19(A)(1) first sentence.
2) Use article 310 to find the minimum suitable conductor that meets the requirements of 210.19(A)(1) second sentence.
3) Select the larger of the conductors selected in 1 and 2 above.
4) Use 210.20(A) to select the minimum OCPD required.
5) Use article 240 to determine if the conductor from step 3 is properly protected by the OCPD from step 4. If the conductor is not properly protected, then select a larger conductor.

1. 100a N-cont + 75 A Cont 30C
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 2/0 Cu conductor.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 3/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 3/0 conductor has an ampacity of 200A at the terminals(75C) and 225A along the run(90C), and is properly protected by a 200A OCPD.
The conductor size to use is 3/0 Cu.

2. 100a N-cont + 75 A Cont 42C
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 2/0 Cu 90C conductor in a 42C ambient has an ampacity of 170A; A 3/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 3/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 3/0 conductor has an ampacity of 200A at the terminals (75C) and 196A along the run (90C derating factor 0.87), and is properly protected by a 200A OCPD.
The conductor size to use is 3/0 Cu.

3. 100a N-cont + 75 A Cont 42C and 4 current carring conductors in conduit.
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 3/0 Cu 90C conductor in a 42C ambient with 4CCC has an ampacity of 157A; A 4/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 4/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 4/0 conductor has an ampacity of 230A at the terminals (75C) and 181A along the run (90C derating factor 0.87 adjustment for CCC 0.8), and is properly protected by a 200A OCPD.
The conductor size to use is 4/0 Cu.

New: 80a N-cont + 100A Cont 42C and 4 current carrying conductors in conduit.
1) Per 210.19(A)(1) first sentence, an ampacity of 180A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 3/0 Cu 90C conductor in a 42C ambient with 4CCC has an ampacity of 157A; A 4/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 205A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 4/0 Cu conductor.
3) Select the 4/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 205A. Per article 240, this next larger standard breaker is a 225A breaker.
5) Under the specified operating conditions, a 4/0 conductor has an ampacity of 230A at the terminals (75C) and 181A along the run (90C derating factor 0.87 adjustment for CCC 0.8), and is _not_ properly protected by a 225A OCPD. A 250kcmil conductor has an ampacity of 202A along the run and _is_ properly protected by a 225A OCPD.
The conductor size to use is 250kcmil Cu.

-Jon

 

[charlie b]

I am having some difficult discerning exactly where the two (or is it more than two) opinions are different from each other. So I will take the coward’s way out, and not (at this time, anyway) state that I agree with XXX and disagree with YYY.

Rather, let me invite to everyone’s attention the words that appear in the title of Article 210.19: “Conductors – Minimum Ampacity and Size.” Now let us take note of the fact that “sentence one” talks about “ampacity,” and the fact that “sentence two” talks about “size.”

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Let me address the second sentence first. Do not be turned from the path of truth by the presence of the word “ampacity” in this sentence; the sentence is about size. If I may be allowed to point out the obvious (because I think it’s important to do so), we can all agree (I do hope) that the size of a conductor does not depend on the ambient temperature (let’s disregard the small amount of swelling at higher temperatures), nor on the number of conductors in a conduit, nor with the percentage of the load that is non-linear. A conductor’s size is based solely on its cross-sectional area, and no matter how we use it, the size of the conductor is not going to change.

So “sentence two” tells us how to pick the minimum size. We take into account the amount of continuous load, and we do not take into account the “conditions of use” to which the conductor will be subjected. That is, what we do it to take 100% non-continuous and add 125% continuous, and look for a conductor that has at least that ampacity. But when we look in Table 310.16 to obtain ampacity values, we can disregard two things shown in that table. One thing we disregard is its statement to the effect that it is based on 30C (which in turn would lead us to the table of “Correction Factors” just underneath it). The other thing that we disregard is its statement to the effect that it is based on not more than three current-carrying conductors (which in turn would lead us to a set of “Adjustment Factors”). Because we are not correcting or adjusting the table values, we do not get to take advantage of 110.14(C), and must therefore use the 75C column.

This will give us a “minimum size.” What is the ampacity of a conductor of that size? Not important! Or at least, it is not important to the second sentence. The ampacity is going to vary with temperature and a host of other things. The ampacity is going to vary with the “conditions of use,” or so the Article 100 definition of “ampacity” would tell us. But the size does not vary with conditions of use, so the ampacity of that size of conductor is not important. Not yet.

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Now let us turn our attention to the first sentence of 210.19(A)(1). Now we are talking about ampacity. But we are not talking about “125% continuous” anymore. We are talking about load, and about conductor ampacity. What is the load? Well, that comes from 220. Does the bit about “125% continuous” show up in 220? Not that I have found. So what do we do? First, we calculate the load per 220. Then we look for a conductor that has at least that much ampacity. But where do we find ampacity? Well, we start with Table 310.16, and we do what it tells us to do about temperature and about more than three current-carrying conductors. After dealing with corrections and adjustments, we eventually come up with a conductor that has sufficient ampacity (under the conditions of use) for the calculated load.

Now we have one more task to do. Look at the conductor we picked, to handle the load, per sentence one. Look at the minimum conductor size, per sentence two. If the one we picked, with ampacity to handle the load, is smaller in size than the minimum size, then we have to change our selection, and use the minimum size.

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Did that resolve anything in anyone’s mind?

 

[bob]

First let me say thanks winnie for you response. The way I am reading 210.19A1 is as follows:
Before the application of any adjustment or correction factors, the minimum
ampacity of a branch circuit that supplies continuous load and non-continuous
shall have an allowable ampacity of 125% of the cont load + 100% of the
non-cont load.


Winnie I removed some of you post so as to shorten it length.

1. 100a N-cont + 75 A Cont 30C
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 2/0 Cu conductor.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 3/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 3/0 conductor has an ampacity of 200A at the terminals(75C) and 225A along the run(90C), and is properly protected by a 200A OCPD.
The conductor size to use is 3/0 Cu.

My method to do this is as follows:
Select the breaker. 100 amps + 1.25 x 75 = 193 amps = 200 amp breaker.
Select a conductor 3/0 capacity is 200 amps at 75C. That agrees with your
answer.

2. 100a N-cont + 75 A Cont 42C
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 2/0 Cu 90C conductor in a 42C ambient has an ampacity of 170A; A 3/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 3/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 3/0 conductor has an ampacity of 200A at the terminals (75C) and 196A along the run (90C derating factor 0.87), and is properly protected by a 200A OCPD.
The conductor size to use is 3/0 Cu.

The calculated load is 193 amps from #1. If you divide the 193 amps by the
temp adjusting factor it gives you the required ampacity. 193/0.87= 222 amps. looking at the ampacity of 3/0 at 90C, it is 225 amps which meets
the requirements. Same as your answer.

3. 100a N-cont + 75 A Cont 42C and 4 current carrying conductors in conduit.
1) Per 210.19(A)(1) first sentence, an ampacity of 175A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 3/0 Cu 90C conductor in a 42C ambient with 4CCC has an ampacity of 157A; A 4/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 194A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 3/0 Cu conductor.
3) Select the 4/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 194A. Per article 240, this next larger standard breaker is a 200A breaker.
5) Under the specified operating conditions, a 4/0 conductor has an ampacity of 230A at the terminals (75C) and 181A along the run (90C derating factor 0.87 adjustment for CCC 0.8), and is properly protected by a 200A OCPD.
The conductor size to use is 4/0 Cu..

From #1 the calculated load is 193 amps. The adjustment factors for temp is
0.87 and for 4 conductors it is 0.80. dividing 193/0.80x0.87= 277 amps 90C.
looking at the table #250 is required. Not the same as your answer.

New: 80a N-cont + 100A Cont 42C and 4 current carrying conductors in conduit.
1) Per 210.19(A)(1) first sentence, an ampacity of 180A is required. We must examine both the 75C column without temperature correction (because of the device terminations) and the 90C column with temperature correction (for the thermal limit of the conductor). A 3/0 Cu 90C conductor in a 42C ambient with 4CCC has an ampacity of 157A; A 4/0 Cu conductor is required.
2) Per 210.19(A)(1) second sentence, an ampacity of 205A is required. Using the 75C column of table 310.16, with no adjustment or correction for current carrying conductors or ambient temperature, this requires a 4/0 Cu conductor.
3) Select the 4/0 Cu conductor.
4) Per 210.20(A) the minimum OCPD required is 205A. Per article 240, this next larger standard breaker is a 225A breaker.
5) Under the specified operating conditions, a 4/0 conductor has an ampacity of 230A at the terminals (75C) and 181A along the run (90C derating factor 0.87 adjustment for CCC 0.8), and is _not_ properly protected by a 225A OCPD. A 250kcmil conductor has an ampacity of 202A along the run and _is_ properly protected by a 225A OCPD.
The conductor size to use is 250kcmil Cu.

The calculated load 80 amps + 1.25 x 100 = 205. 225 amps breaker required.
Using the adjustment factors 0.80 x 0.87 = 0.696. Calculated load is 205 A
205A/0.696 = 295 amps at 90C. 250 kcm required. For the most part we agreed. I am suprised. I think your method does not provide the correct answer in #3. I think someone should, not me, write to the committee and have this cleared up.

 

[charlie b]

I am at work, and don't have time to look at either of your math. But let me comment on this (I added emphasis on two words):

The way I am reading 210.19A1 is as follows: Before the application of any adjustment or correction factors, the MINIMUM AMPACITY of a branch circuit that supplies continuous load and non-continuous shall have an allowable ampacity of 125% of the cont load + 100% of the non-cont load.

Not true, though I am not yet sure if it makes a difference. It does not say that this is the miinimum ampacity. What it says is that the smallest conductor you can use is one that has that ampacity.