Kindly advise 215.2 (A) (1)

Smart $

Esteemed Member
Location
Ohio
Ohh! I keep forgetting a point I want to make because I get rapt up in replyig to your statements...

The second sentence of 215.2(A)(1) states "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."

If you use a 90?C conductor on 75?C terminals, your method of determining minimum size is with the 75?C column of Table 310.15(B)(16) using the noncontinuous load plus 125% of the continuous load.

What is the point of the conditional clause "before the application of any adjustment or correction factors" if after the application of any adjustment or correction factors to the 90?C allowable ampacity, the maximum permitted ampacity is still the minimum size determined with the extra 25% for continuous (at the 75?C rating)??? The final derated ampacity must overcome the extra 25% for continuos loading twice... before making any difference.


There was once a posting by the original proposer of 110.14(C) explaining how the original intent was not to duplicate the extra 25% for continuous loading. I tried to find it, but could not.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Nor would I want you to. FWIW, I respect your sticking to your beliefs. :thumbsup:
Likewise :)


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].
110.14(C)(1) says the conductor ampacities used in the determination should be based no Table 310.15(B)(16). (As an aside, I will point out here, that Table 310.15(B)(16) is a Table for "Allowable Ampacities" - but you do not feel that 110.14(C) applies to "Allowable Ampacities".)

Of course it does not say to do so by way of 215.2(A)(1). As has been pointed out, and we have both been in agreement, 215.2 doesn't have anything to do with the ampacity of a conductor, only with determining what the minimum ampacity of a conductor needs to be for the given feeder, and what the minimum conductor size needs to be for the given feeder.

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.
Would you accept "Because the Code requires me to" as a legitimate answer? 110.14(C) says that the temperature rating associated with the ampacity of a conductor shall be selected an coordinated so as not to exceed the lowest temperature rating of any connected device. The second sentence of 215.2(A)(1) establishes a minimum conductor size based on an ampacity of a conductor which is not less than the non-continuous load plus 125% of the continuous load. The temperature rating associated with the required ampacity from second sentence of 215.2(A)(1) must be 75?C if the devices/terminations are rated for 75?C.


I see two parts to 215.2(A)(1):...and...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.

The Code only gives one definition for ampacity. An "allowable ampacity" is undoubtedly an ampacity.


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???
There is no predominance of one part of 215.2(A)(1) over another. BOTH parts of 215.2(A)(1) must comply with 110.14(C) in the same manner. Both parts of 215.2(A)(1) establish a minimum ampacity ("ampacity not less than".) The first part establishes an ampacity to ensure that the conductor can supply the load. The second part establishes an ampacity to provide for a minimum conductor size. 110.14(C) (which is a General Requirement of the Code) requires that the temperature rating associated with the ampacity of a conductor shall be 75?C if the lowest rating of any connected device, conductor or termination is 75?C.

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).
Yes, my gripe is with the way you are trying to seek compliance with 110.14(C). (I guess you could say that that makes my gripe with your first step, but it is also clearly with your second step.) You are applying 110.14(C) to determine a minimum conductor size. There is NOTHING in 110.14(C) about determining a minimum conductor size. As we have seen, the second part of 215.2(A)(1) establishes a minimum conductor size, and the first part of 215.2(A)(1) establishes a minimum ampacity for a feeder (which may require a larger conductor than the established minimum conductor size.)

To comply with 110.14(C), you must establish the temperature rating that is to be associated with the ampacity of a conductor. And the temperature rating must not exceed the lowest rating of any connected device, termination or conductor. If I have terminations rated 75?C on my feeder, and I select an ampacity of a given conductor size associated with the 90?C rating of the conductor insulation, then I have just violated 110.14(C).


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)???
I HAVE used the calculated load here together with 110.14(C). In fact, my determination of the need for either parallel 600mcm THWN or 500mcm THWN-2 is DIRECTLY from 110.14(C). I have determined that parallel sets of 500mcm THWN-2 will have an ampacity that is too small for the load. I would either have to use a larger conductor (the parallel 600mcm is large enough to supply the load) OR using 110.14(C)
Conductors with temperature ratings higher than specified for termination provisions shall be permitted to be used for ampacity adjustment, correction, or both.
I can use parallel 500mcm THWN-2.


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
Here are a couple of more....

http://www.iaei.org/magazine/2003/07/sizing-conductors-for-all-load-conditions/

http://ecmweb.com/content/sizing-continuously-loaded-conductors-made-simple

The one from EC&M is interesting because it was written at the time the the Code was changed to introduce this language. It gives much better explanations of the 125% of continuous load rule than I can.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Ohh! I keep forgetting a point I want to make because I get rapt up in replyig to your statements...

The second sentence of 215.2(A)(1) states "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."

If you use a 90?C conductor on 75?C terminals, your method of determining minimum size is with the 75?C column of Table 310.15(B)(16) using the noncontinuous load plus 125% of the continuous load.

What is the point of the conditional clause "before the application of any adjustment or correction factors" if after the application of any adjustment or correction factors to the 90?C allowable ampacity, the maximum permitted ampacity is still the minimum size determined with the extra 25% for continuous (at the 75?C rating)???
The EC&M article (post 42) addresses this pretty well. It says
The Code now requires building in an additional 25% of the continuous portion of a load when sizing conductors. This provides "headroom" at the termination so that heat can be dissipated more easily.
In your post #7, when you determine in step 1 that you need 2 sets of 400mcm for the 650A load, and then you determine in step 2 that you need 400mcm (90?C rating) for the continuous load factor, you have effectively wiped out this "headroom."


The final derated ampacity must overcome the extra 25% for continuos loading twice... before making any difference.
I'm not sure that I understand what you are saying here. Perhaps you could provide an example.

But I don't see any need for the final derated ampacity to overcome the extra 25% twice. Going back to post #7, if parallel sets of 400mcm can handle the load (without and adjustment/correction) and the extra 25% bumps this up to parallel sets of 500mcm, then that SINGLE step of making the minimum conductor size parallel sets 500mcm has addressed the 25%. There is no reason to revisit it. Now if I need to address any ampacity correction or adjustment, I would start at my minimum conductor size of parallel 500mcm and apply my correction/adjustment factors and make sure that my ampacity is large enough to supply the load.

In the original example, two sets of 500mcm (90?C) had an adjusted ampacity of 2*430A*0.92 = 791A, which is large enough to supply the load.

If the two sets of 500mcm (90?C) had to supply the 650A load in an ambient of 36?C with 6 ccc's in the raceway, then it would have an ampacity of 2*430A*0.91*0.8 = 626A. This is too small to supply the load. You would need a larger conductor.

If the two sets of 500mcm (90?C) had to supply the 650A load in an ambient of 31?C with 6 ccc's in the raceway, then it would have an ampacity of 2*430A*0.96*0.8 = 660A. This is large enough to supply the load.

If the two sets of 500mcm (75?C) had to supply the 650A load in an ambient of 36?C with 3 ccc's in the raceway, then it would have an ampacity of 2*380A*0.88 = 669A. This is large enough to supply the load.

As you can see, once the 25% for continuous load is added to establish a minimum conductor size, there is no need for the adjusted ampacity to overcome the 25% a second time.
 

Smart $

Esteemed Member
Location
Ohio
Likewise :)

...
Well, I could go on an on about this. However, typing it all up would be a waste of my time and yours, for I have decided to change to your method under the premise it appears to be the industry standard.

I appreciate your time and effort on this matter. :happyyes:
 

m sleem

Senior Member
Location
Cairo
1) Minimum size of conductor for terminal temperature limitations (using calculated load value; does not include 125% factoring for continuous loads).
&
3) Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load (does not include 125% factoring for continuous loads).
Smart,
Could you send the code reference for those two ?
 

Smart $

Esteemed Member
Location
Ohio
Smart,
Could you send the code reference for those two ?
1) 110.14(C)(1)(b)(2)*

3) 215.2(A)(1) first sentence

*After earlier deliberation with David, I conceded that industry standard method includes the extra 25% for continuous portion of load.

PS: You may also be interested in the post/thread I linked to in Post #45...
 
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Smart $

Esteemed Member
Location
Ohio
Excellent spread sheet! Thanks very much.:)
You are welcome. :D


The latest version (with a found error corrected and some minor formatting changes) isn't the one attached to the post I originally linked.

Make sure you get the one from the Google Docs link a few post later.
 

m sleem

Senior Member
Location
Cairo
I was always thinking the termination lug is only bare conductor & no correction has to be considered in termination sizing since the size of cable is already indicated in terminal it self.​
 

Smart $

Esteemed Member
Location
Ohio
I was always thinking the termination lug is only bare conductor & no correction has to be considered in termination sizing since the size of cable is already indicated in terminal it self.​
Well it's analogous to, "If the shoe fits, wear it."

Shoe fit is no guarantee of all-day comfort or longevity.
 

Smart $

Esteemed Member
Location
Ohio
You are welcome. :D


The latest version (with a found error corrected and some minor formatting changes) isn't the one attached to the post I originally linked.

Make sure you get the one from the Google Docs link a few post later.
New version uploaded.

https://docs.google.com/file/d/0By0rzU3UuNh7eHYwdS1QdTRCNHc/edit?usp=sharing

Just added some conditional formatting for "change input" messages.

In future I will only be notifying of newer versions in the Excel Docs thread.
 

ToolHound

Senior Member
Generally (with emphasis), conductor sizing is a four-step process...

1) Minimum size of conductor for terminal temperature limitations (using calculated load value; does not include 125% factoring for continuous loads).

2) Minimum ampacity of conductor before adjustment and correction must equal or exceed 125% continuous plus noncontinuous sum of calculated load.

3) Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load (does not include 125% factoring for continuous loads).

4) The overcurrent protection device must have a rating not less than 125% continuous plus noncontinuous sum of calculated load. The adjusted and corrected conductor ampacity must at a minimum be greater than next smaller standard overcurrent device rating [240.4(B); does not apply in all instances]. Where 240.4(B) does not apply, the adjusted and corrected conductor ampacity must equal or exceed overcurrent protection rating.

Ultimately, the chosen conductor must meet all four requirements.


EDIT to add: Calculated load includes demand factoring.
Smart $. I am drilling on the well stated information in your post (copied above). Of course, this information is in the Code and in other books. I like the way the steps are stated in your post. Just so I understand as well as possible, I would like to ask...what was your change, if any, in the wording in the step 3 of your post copied above? I may misundertand, so let me ask...did you decide that...
Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load ( including 125% factoring for continuous loads)? I saw the thread discussion and just wanted to double check if I understand your meaning regarding step 3.

Thanks, ToolHound
 
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Smart $

Esteemed Member
Location
Ohio
Smart $. I am drilling on the well stated information in your post (copied above). Of course, this information is in the Code and in other books. I like the way the steps are stated in your post. Just so I understand as well as possible, I would like to ask...what was your change, if any, in the wording in the step 3 of your post copied above? I may misundertand, so let me ask...did you decide that...
Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load ( including 125% factoring for continuous loads)? I saw the thread discussion and just wanted to double check if I understand your meaning regarding step 3.

Thanks, ToolHound
No. Step 3 is just a paraphrasing of the first sentence of 215.2(A)(1), while Step 2 is a paraphrasing of the second sentence.

What needs changed is Step 1...

Generally (with emphasis), conductor sizing is a four-step process...

1) Minimum size of conductor for terminal temperature limitations (using calculated load value with 125% factoring for continuous loads).

2) Minimum ampacity of conductor before adjustment and correction must equal or exceed 125% continuous plus noncontinuous sum of calculated load.

3) Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load (does not include 125% factoring for continuous loads).

4) The overcurrent protection device must have a rating not less than 125% continuous plus noncontinuous sum of calculated load. The adjusted and corrected conductor ampacity must at a minimum be greater than next smaller standard overcurrent device rating [240.4(B); does not apply in all instances]. Where 240.4(B) does not apply, the adjusted and corrected conductor ampacity must equal or exceed overcurrent protection rating.

Ultimately, the chosen conductor must meet all four requirements.
 

Smart $

Esteemed Member
Location
Ohio
BTW, I'm still not entirely convinced that is the proper way to apply 110.14(C), but I concede to it because I couldn't find any authoritative information to back it up... and plenty to the contrary. However, there once was a discussion here on the subject (probably been several years) where the original proposal submitter either explained what he intended by posting, or someone else provided an accounting of his details. I have searched and cannot find that thread. If anyone else can, please post a link to it...

Anyway, IIRC, the intent was to use the calculated load without 125% factoring for continuous loads to determine the terminal temperature limitation. The concept was that upon using 125% continuous load factoring in determining ampacity under 215.2 (or 210.19) would guarantee the wire temperature would never reach the terminal temperature limit under nominal operating conditions. To determine the terminal temperature imitation with 125% factoring for continuous loads actually doubles the application of the factoring.
 

ToolHound

Senior Member
Generally (with emphasis), conductor sizing is a four-step process...

1) Minimum size of conductor for terminal temperature limitations (using calculated load value with 125% factoring for continuous loads).

2) Minimum ampacity of conductor before adjustment and correction must equal or exceed 125% continuous plus noncontinuous sum of calculated load.

3) Minimum ampacity of conductor after adjustment and correction must equal or exceed calculated load (does not include 125% factoring for continuous loads).

4) The overcurrent protection device must have a rating not less than 125% continuous plus noncontinuous sum of calculated load. The adjusted and corrected conductor ampacity must at a minimum be greater than next smaller standard overcurrent device rating [240.4(B); does not apply in all instances]. Where 240.4(B) does not apply, the adjusted and corrected conductor ampacity must equal or exceed overcurrent protection rating.

Ultimately, the chosen conductor must meet all four requirements.

No. Step 3 is just a paraphrasing of the first sentence of 215.2(A)(1), while Step 2 is a paraphrasing of the second sentence.

What needs changed is Step 1...
Smart $ Thanks. Ok. Well, just wondering, so that I will know where in the book to go when I forget and need to refresh my memory, is there any particular Code section(s) that I can point to to show that step 3 does not include 125% factoring for continuous loads ? I agree with what you're saying...I just hope to find anything in the book that will back me up.

Thanks, ToolHound
 

Smart $

Esteemed Member
Location
Ohio
No. Step 3 is just a paraphrasing of the first sentence of 215.2(A)(1), while Step 2 is a paraphrasing of the second sentence.

What needs changed is Step 1...
Smart $ Thanks. Ok. Well, just wondering, so that I will know where in the book to go when I forget and need to refresh my memory, is there any particular Code section(s) that I can point to to show that step 3 does not include 125% factoring for continuous loads ? I agree with what you're saying...I just hope to find anything in the book that will back me up.

Thanks, ToolHound
See emphasized text in quote of my post.

Note first sentence of 215.2(A)(1) uses only the word "ampacity", rather than "allowable ampacity" as in the second sentence. The term "allowable ampacity" refers to the values expressed in the ampacity tables. You can confirm this by looking at the table header text. The term "ampacity", without any modifying words, generally means after adjustment and correction factors for the conditions of use have been applied to the table values.
 
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ToolHound

Senior Member
See empasized text in quote of my post.

Note first sentence of 215.2(A)(1) uses only the word "ampacity", rather than "allowable ampacity" as in the second sentence. The term "allowable ampacity" refers to the values expressed in the ampacity tables. The term "ampacity", without any modifying words, means after adjustment and correction factors for the conditions of use have been applied to the table values.
Smart $. Ok. Got it. Thanks. --ToolHound
 
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