Rooftop adjustment...

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iwire

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I understand it is not required... by convention. The wording itself is neither explicit nor concise enough to say what way it should or shouldn't be done.

...and it wasn't the last sentence of 110.14(C) "general statement" that I am referencing... (see highlighted quote of text below).

General statement does say you cannot exceed the lowest rated temperature.

Subparagraph (1) says to base ampacities on Table 310.16. Is not ambient temperature correction a part of Table 310.16? (a)(2) and (b)(2) do use the word "ampacity" and per Table 310.16 ambient correction is required for conductor ampacity.



However, one must apply adjustments appropriately. Take for example Norb's situation where most of the run is on the roof but both ends of the run(s) drop down into and are terminated in a 30?C living area. Conventional application of using a higher temperature-rated conductor for termination adjustment would be appropriate.

Yet again, let's say we have a similar scenario but the load end(s) terminate on the roof into 75?C-rated mechanical lugs and the supplied devices, equipment, and such has an equivalent or better temperature rating. The first sentence of 110.14(C) says we must select and coordinate the ampacity so as not to exceed the lowest temperature rating of any connected termination, conductor, or device... which is 75?C in this case. So do we not have to correct for ambient temperature the tabled 75?C ampacity to determine the current level at which the conductor exceeds 75?C?

What if there are more than 3 ccc's in the run? Again the key here is by the first sentence of 110.14(C), we have to determine at what current level does the size used exceed the permitted temperature.


I have no clue at all what your trying to say here.:confused:

I know you think it's clear but for me it's like trying to find Waldo.

IMO this is what matters

Conductors with temperature ratings higher than specified
for terminations shall be permitted to be used for ampacity
adjustment, correction, or both.
 
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infinity

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I have no clue at all what your trying to say here.:confused:

I know you think it's clear but for me it's like trying to find Waldo.

IMO this is what matters



Conductors with temperature ratings higher than specified
for terminations shall be permitted to be used for ampacity
adjustment, correction, or both

That does it for me.
 

Smart $

Esteemed Member
Location
Ohio
I have no clue at all what your trying to say here.:confused:

I know you think it's clear but for me it's like trying to find Waldo.
Conventional wisdom at its finest??? ;)

It seems that anytime a concept which shakes the foundation of the premise upon which conventional widom is placed, everyone puts on their own personalized pair of blinders. :D

IMO this is what matters
Conductors with temperature ratings higher than specified
for terminations shall be permitted to be used for ampacity
adjustment, correction, or both
I agree that matters. I am not contesting that issue. What I am trying to point out is what seems to me to be an error in its implementation... not in its entirety but under certain, perhaps common circumstances.

Would you agree the concept of termination temperature ratings is to set a maximum temperature—it is absolute temperature and not relative, right?— for which the termination will perform adquately? Exceeding that temperature will have a degrading effect on the integrity of said termination, right?

Let's use an example... According to Table 310.16 we are to assume a #12 Cu wire will be operating at 75?C when it is conducting 25 amperes of current. Correct? We generally say yes but in fact that is conditional upon the ambient temperature. If the ambient temperature were 45?C, would the wire's temperature be 75?C when conducting 25 amperes of current, or would it be greater than 75?C? The answer we must assume from the Table is that it would be greater than 75?C because it has us multiply by a factor of 0.82 to adjust a 75?C-rated conductor's ampacity.

What I'm saying is that when the ambient temperature at the location of the termination is not 30?, it seems we should be adjusting the ampacity for our 75?C reference value from the Table when using a higher-rated-temperature wire for the purpose of ampacity adjustment, correction, or both.
 

yired29

Senior Member
Conventional wisdom at its finest??? ;)



What I'm saying is that when the ambient temperature at the location of the termination is not 30?, it seems we should be adjusting the ampacity for our 75?C reference value from the Table when using a higher-rated-temperature wire for the purpose of ampacity adjustment, correction, or both.

110.14 (C) Temperature Limitations. 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. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

THHN wire 90 degree we can derate from the 90 degree column. Be sure we do not exceed the temperature at the point of terminantion so a #12 @ 25 amps will be 75 degrees
 

iwire

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Staff member
Location
Massachusetts
Conventional wisdom at its finest??? ;)

It seems that anytime a concept which shakes the foundation of the premise upon which conventional widom is placed, everyone puts on their own personalized pair of blinders. :D

Yes and that is sometime very helpful when dealing with the NEC.:grin:

I have no interest in picking the fly poop out of the black pepper. Maybe it's because we have had so much of this type of post lately.

Al H, is telling is a wall switch box is an outlet.

Mike W is telling us a fixture bar and a clamp that has been removed from a box both count against conductor fill.

Mark is telling us we always have to follow the small conductor rules.


Sometimes I think the blinders do help us, most of us know how all the above rules apply it is only when we try to find a problem that we do find a possible wording problem.


Would you agree the concept of termination temperature ratings is to set a maximum temperature?it is absolute temperature and not relative, right?? for which the termination will perform adequately?

I don't know, I used to agree with that but even that was questioned within the last month.



Let's use an example... According to Table 310.16 we are to assume a #12 Cu wire will be operating at 75?C when it is conducting 25 amperes of current. Correct?

I would say it will not operate above 75 C, as to what it's actual temp is no one can predict.


If the ambient temperature were 45?C, would the wire's temperature be 75?C when conducting 25 amperes of current, or would it be greater than 75?C? The answer we must assume from the Table is that it would be greater than 75?C because it has us multiply by a factor of 0.82 to adjust a 75?C-rated conductor's ampacity.

I agree that is what we can assume.

What I'm saying is that when the ambient temperature at the location of the termination is not 30?, it seems we should be adjusting the ampacity for our 75?C reference value from the Table when using a higher-rated-temperature wire for the purpose of ampacity adjustment, correction, or both.

And I am saying above and beyond all our collective thoughts the code makes clear we do not have to do as you suggest.

If it's an error or if 'they' just know something we don't I don't know nor care.:)
 

Smart $

Esteemed Member
Location
Ohio
Yes and that is sometime very helpful when dealing with the NEC.:grin:

I have no interest in picking the fly poop out of the black pepper. Maybe it's because we have had so much of this type of post lately.

...[blah, blah, blah]...

Sometimes I think the blinders do help us, most of us know how all the above rules apply it is only when we try to find a problem that we do find a possible wording problem.
Helpful in what sense... peace-o-mind? ;)

My only concern on the issue is compliance with the wording of the code, or the intent of the wording if the wording is in error. The latter should be recognized and fixed, rather than "grandfathered" in because its has served us well in the past. When adopted into law by various AHJ's, it becomes a legally-binding document which has meanings that, if taken to court, can and will be interpretted through its wording by non-expert persons. Certainly experts can be brought forth, but it is hard for an expert to say the wording isn't meant to mean how it reads. It makes the so-called expert appear non-credulous and defeats the purpose for which he/she has been called to testify.

As for picking fly poop out of [ground] black pepper, if there's money in it for a lawyer and/or his/her firm, you can bet the livestock?and the flies that come with 'em?on it they will.

I don't know, I used to agree with that but even that was questioned within the last month.
It should be questioned. Actually I find the concept of termination temperature rating quite baffling from the absolute temperature perspective. I believe if you were to both make and operate the termination in a 60?C ambient environment, you could operate the conductors to a substantial temperature rise above that, even exceeding 75?C and 90?C and not compromise the electrical integrity of the connection no more than making the connection in a 30? environment and operating at 75?... as it is the expansion and contraction of the associated parts which contribute to the loss of integrity to the electrical connection.


I would say it will not operate above 75 C, as to what it's actual temp is no one can predict.
Fair point... but one (rather scientific chap at that) can predict the temperature... as to how accurate the prediction... ??? ;)

Yet in complying with the code, do we not have to do so within the its rules. If I were an engineer, and anal retentive enough to do so, I'd use the "under engineering supervision" out in every case permitted. :D

I agree that is what we can assume.
Well I'm glad we can at least agree to assume the same thing :roll:

And I am saying above and beyond all our collective thoughts the code makes clear we do not have to do as you suggest.
And here is where you put on your blinders. What I'm saying is that it isn't as clear as you make it or perceive it to be. Perhaps I'm dissing you, and I can't say it's not intended... but understand it isn't personal as it is a failing in most humans, as we are creatures of habit and contentment. Even I am guilty in that respect... just not on this issue... :cool:

If it's an error or if 'they' just know something we don't I don't know nor care.:)
Who knows!!! I think the CMP members don't know for certain half the time. I can live with the way it is... but I think it would be better worded if when referring to "60?C ampacity" and "75? ampacity" in the sub-sub-paragraphs, it would be more likened to conventional approach if it were worded "non-adjusted 60?C ampacity" and "non-adjusted 70?C ampacity". Then it doesn't matter how scientifically it is in error... the method of implementation would then be clear[-er] ;)
 

Smart $

Esteemed Member
Location
Ohio
THHN wire 90 degree we can derate from the 90 degree column. Be sure we do not exceed the temperature at the point of terminantion so a #12 @ 25 amps will be 75 degrees
Agreed... but that's it's rating in a 30?C ambient temperature environment. What would the ampacity be in a 50?C environment?
 

Smart $

Esteemed Member
Location
Ohio
... but I think it would be better worded if when referring to "60?C ampacity" and "75? ampacity" in the sub-sub-paragraphs, it would be more likened to conventional approach if it were worded "non-adjusted 60?C ampacity" and "non-adjusted 70?C ampacity". Then it doesn't matter how scientifically it is in error... the method of implementation would then be clear[-er] ;)

This last part of my post may be rendered moot in the 2011 edition, as going by the draft, the ambient temperature adjustment is being removed from the Table.
 

iwire

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Staff member
Location
Massachusetts
Helpful in what sense... peace-o-mind? ;)

In the sense of 'Don't sweat the small stuff and get the job done'.

My only concern on the issue is compliance with the wording of the code, or the intent of the wording if the wording is in error. The latter should be recognized and fixed, rather than "grandfathered" in because its has served us well in the past.

I do not disagree, so put in a proposal instead of confusing people about what the NEC minimums are with your own agenda.:grin:


Fair point... but one (rather scientific chap at that) can predict the temperature... as to how accurate the prediction... ??? ;)

Of course it can be predicted .... with enough data, but based on the info you provided it could not be predicted.


And here is where you put on your blinders.

Yes, I admitted it and enjoy it.:cool:


What I'm saying is that it isn't as clear as you make it or perceive it to be. Perhaps I'm dissing you, and I can't say it's not intended... but understand it isn't personal as it is a failing in most humans, as we are creatures of habit and contentment. Even I am guilty in that respect... just not on this issue... :cool:

And what I am saying is often people try to place themselves on a higher intellectual plain convincing themselves they have found a problem that others do not see as a problem. Then they simply try to talk down to those that do not see things the same way. Even I am guilty in that respect... just not on this issue... :cool:
 

Smart $

Esteemed Member
Location
Ohio
In the sense of 'Don't sweat the small stuff and get the job done'.
Typical foreman-type trash talk ;)


I do not disagree, so put in a proposal instead of confusing people about what the NEC minimums are with your own agenda.:grin:
Me... an agenda!!! If you knew me better (not saying that is desired ;)), you definitely wouldn't accuse me of such.

As to putting in a proposal, I'll have to wait and see what differences the 2011 edition make... if still up in the air, I very well may do so for the 2014 edition.

Of course it can be predicted .... with enough data, but based on the info you provided it could not be predicted.
Perhaps not predicted accurately, but there is enough info to adjust the 75?C value used for comparison.

Yes, I admitted it and enjoy it.:cool:
It's not like we didn't know that already ;)

And what I am saying is often people try to place themselves on a higher intellectual plain convincing themselves they have found a problem that others do not see as a problem. Then they simply try to talk down to those that do not see things the same way. Even I am guilty in that respect... just not on this issue... :cool:
...and other times the condescension is founded, while the person on the "other" intellectual plane attempts reverse psychology, which only serves to betray their true disposition. See Peter D's response ;)
 

iwire

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Staff member
Location
Massachusetts
Me... an agenda!!!

Yes, you.

...and other times the condescension is founded, while the person on the "other" intellectual plane attempts reverse psychology, which only serves to betray their true disposition.

My true disposition has been a mater of public record for long time, I doubt you just learned anything new. :grin:
 

rettich

Member
Location
Troy, Michigan
Above 36 inches on roof

Above 36 inches on roof

A question came to me about conduits on a roof supported over 36 above the roof. Do these conduits just need to be rated for the ambient local temperature? I don't see anything that says anything for anything above 36 inches. This is dealing with table 310.15(B)(2)(c)
 
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