conductor derating help

[omega83]

I'm a little confuse again on conductor derating. Can some one put me back on the right track.

Say a general Test question ask, You have a 1" EMT conduit with 5 #6 THWN wire. Temp is at 107 F. What is the amp of the wires?

I understand how to derate but I get confuse of which coloum to use to get my ampacities now. I was on you tube and saw mike holts nec 2011 conducotr size terminal rating. He said that if they don't specified the ampacity terminal rating, then you have to use 60 degree coloum for derating because of 110.14 (c)1. In T 310.15(b)(16) off the 2011 nec, they have 60 degrees,75 degrees or 90 degrees coloums. I see that THWN is in the 75 degrees and thats what I always did. Do I derate the conductors in 60 degrees or 75 degrees coloum? Do I go by what type of wire it is which is 75 degrees for THWN?

 

[infinity]

You would use the ampacity of the conductor based on it's insulation value for derating. The terminal value doesn't matter when adjusting the ampacity of the conductor. Also your example question is unanswerable becauyse it fails to state what those 5 conductors actually are. Only CCC's would count towards derating.

 

[DavidA]

If the conductors being used are rated 90C then you can use the 90c table for adjustment or correction.

 

[Twoskinsoneman]

You would use the ampacity of the conductor based on it's insulation value for derating. The terminal value doesn't matter when adjusting the ampacity of the conductor. Also your example question is unanswerable becauyse it fails to state what those 5 conductors actually are. Only CCC's would count towards derating.

Is it not true that non-CCCs also have to be derated for higher ambient temps such as in the OP?

 

[augie47]

Is it not true that non-CCCs also have to be derated for higher ambient temps such as in the OP?

It's true as far as ambient derating. That affectes all conductors, but you could not really answer the question without knowing the number of CCC so you know how to apply 310.15(B)(2).

 

[Twoskinsoneman]

I agree. Although with most questions I had in my studying (Mike's Books), and then when I actually took my test it was generally assumed that unless noted all conductors were assumed to be CCCs.

Since the OP was identified as a test question I would stick with that assumption

 

[augie47]

I'm a little confuse again on conductor derating. Can some one put me back on the right track.

Say a general Test question ask, You have a 1" EMT conduit with 5 #6 THWN wire. Temp is at 107 F. What is the amp of the wires?

I understand how to derate but I get confuse of which coloum to use to get my ampacities now. I was on you tube and saw mike holts nec 2011 conducotr size terminal rating. He said that if they don't specified the ampacity terminal rating, then you have to use 60 degree coloum for derating because of 110.14 (c)1. In T 310.15(b)(16) off the 2011 nec, they have 60 degrees,75 degrees or 90 degrees coloums. I see that THWN is in the 75 degrees and thats what I always did. Do I derate the conductors in 60 degrees or 75 degrees coloum? Do I go by what type of wire it is which is 75 degrees for THWN?

One of the things that makes tests interesting is determining exactly what is being asked. The "ampacity" of the wire would be calculated using the temperature rating. (as noted there is not enough info in the OP to determine the final answer).
My intent is to point out they are asking for the ampacity with no mention of terminating.
The info you read from Mike is critical as far as the actual installation as 100.14 determines what ratings can be used once the ampacity is determined. It's very easy to read too much into a question.

 

[augie47]

I agree. Although with most questions I had in my studying (Mike's Books), and then when I actually took my test it was generally assumed that unless noted all conductors were assumed to be CCCs.

Since the OP was identified as a test question I would stick with that assumption

Since they mentioned the number of conductors, I agree. I would look for the answer that approached it as all 5 being CCCs.
(Developing good questions is more difficult than answering them)

 

[cadpoint]

I'm only going to talk about Table 310.16.

It's just well misunderstood in respects to appling the first part to get to the second part.

Pick a wire type, drop down column to a required size and note, "Size AWG" then go find that in the 60 degree column and get the required "Size AWG"
Then drop down to Corrections then apply that, that includes where ever the A. Temp. is. After that math then go find another wire in the 60 degree column.

Yes, it's what was said to do...

Then realize that Table 310.16 is for only 3 current carring in raceway so One will need another number to
use along with other possible deductioins.

 

[infinity]

Is it not true that non-CCCs also have to be derated for higher ambient temps such as in the OP?

Good question, but where does it say that you would apply ambient temperature correction to non CCC's?

 

[omega83]

One of the things that makes tests interesting is determining exactly what is being asked. The "ampacity" of the wire would be calculated using the temperature rating. (as noted there is not enough info in the OP to determine the final answer).
My intent is to point out they are asking for the ampacity with no mention of terminating.
The info you read from Mike is critical as far as the actual installation as 100.14 determines what ratings can be used once the ampacity is determined. It's very easy to read too much into a question.

Okay so what you guys are saying is that they are looking for the ampacity of the wire not the termination. So THWN would have to be size in the 75 degrees coloumn. I guess this can get confusing because no matter what, there has to be a termination point and the question never stated that. If the question only gave me a wire type, then I would have to see what coloumn it falls under right? But if I use the same question and add that it has a Overcurrent Protection of 60amps and does not state termination ratings. Then I would have to fall under 110.14 thats under 100amps at 60 degree coloumn, RIGHT?

 

[augie47]

Sounds correct. You use the column corresponding to your conductor insulation for derating. Then, IF you know the termination details, that may limit your ampacity.
For example, if you had a #4 wire and the de-rated ampacity calculated to 76 amps and it terminated on a 60 amp breaker you knew no other details, your ampacity would then be
70 amps.

 

[Twoskinsoneman]

Good question, but where does it say that you would apply ambient temperature correction to non CCC's?

I don't see anything that excludes non-CCC's

When I dissect the description of table 310.16 I don't believe it excludes non-CCCs.

Table 310.16 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60?C Through 90?C (140?F Through
194?F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient
Temperature of 30?C (86?F)

 

[infinity]

I don't see anything that excludes non-CCC's

When I dissect the description of table 310.16 I don't believe it excludes non-CCCs.

Table 310.16 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60?C Through 90?C (140?F Through
194?F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient
Temperature of 30?C (86?F)

I see your point based on the heading of the table and the fact that the ampacities is are based on 30? C. Is there any other verbiage in the NEC that says this is for non-CCC's? Admittedly it makes sense to apply temperature correction factors to all conductors.

 

[jumper]

I see your point based on the heading of the table and the fact that the ampacities is are based on 30? C. Is there any other verbiage in the NEC that says this is for non-CCC's? Admittedly it makes sense to apply temperature correction factors to all conductors.

Small rant. Use "wording".

Definition of VERBIAGE
1
: a profusion of words usually of little or obscure content.

http://www.merriam-webster.com/dictionary/verbiage

 

[kingpb]

I'm a little confuse again on conductor derating. Can some one put me back on the right track.

Say a general Test question ask, You have a 1" EMT conduit with 5 #6 THWN wire. Temp is at 107 F. What is the amp of the wires?

I understand how to derate but I get confuse of which coloum to use to get my ampacities now. I was on you tube and saw mike holts nec 2011 conducotr size terminal rating. He said that if they don't specified the ampacity terminal rating, then you have to use 60 degree coloum for derating because of 110.14 (c)1. In T 310.15(b)(16) off the 2011 nec, they have 60 degrees,75 degrees or 90 degrees coloums. I see that THWN is in the 75 degrees and thats what I always did. Do I derate the conductors in 60 degrees or 75 degrees coloum? Do I go by what type of wire it is which is 75 degrees for THWN?

If the conductor is rated for only 75 deg C then it can carry the current as listed in 310.16 75 deg C column under those conditions. Then you start your derating to determine maximum operating current.

With the limited information of the question, I would have to assume that the 5 conductors are all current carrying, this will provide the worst case.

310.16, #6 AWG, THWN, 75 deg C is rated for 65A at 30 deg C. Then for temperature of 107deg F, you have to multiply 65A x 0.82 = 53.3A. However, with 5 conductors you have to look at 310.15.(B)(2)(a) and the 53.3A is further reduced to 80%, e.g. 53.3A x 0.8 = 42.6A.