90 C conductor ampacity rating.

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cukele

Member
When sizing conductors, can the 90C rating of a conductor be used only when derating for temperature, if not when can the ampacity rating for a cable rated at 90C be used?
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Welcome to the forum.:)

Yes, if you have a conductor with a 90 degree rating you can use the 90 degree ampacity rating to start your ampacity adjustment calculations.

Keep in mind that the final ampacity can't exceed the value of the conductor from the temperature coulmn for the lowest rated terminal the conductors are terminated on.

Chris
 

chris kennedy

Senior Member
Location
Miami Fla.
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60 yr old tool twisting electrician
When sizing conductors, can the 90C rating of a conductor be used only when derating for temperature, if not when can the ampacity rating for a cable rated at 90C be used?


Welcome to the Forum. I use it for all adjustments.

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.
 

cukele

Member
So, the 90C rating can only be used when derating if the termination lugs of the equipment are rated 90C.
I work with an electrical engineer who always uses 90C cable to get a higher rating for the conductors, even when no derating factors are required.
How can the insulation class justify a higher amp rating? I assume the the 90C cable is rated to protect from foreign heat sources. Is this assumption correct?
 

Smart $

Esteemed Member
Location
Ohio
When sizing conductors, can the 90C rating of a conductor be used only when derating for temperature, if not when can the ampacity rating for a cable rated at 90C be used?
There are at least two instances where a 90?C-rated conductor can be used at it's full ampacity rating. One such scenario is under 310.15(A)(2) Exception. The other is installations qualifying under 110.14(C)(2) for 600V and less. Only if identified otherwise is the any limitation for over 600V.

One debatedly practical application is to go from 75?C-rated size to 90?C-rated size conductor by joining circuit conductors in a terminal box with 90?C-rated terminations (i.e. terminal strips, splice blocks, etc.). Of course the enclosure itself also needs to be rated for 90?C or higher operationn.
 

jim dungar

Moderator
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Location
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PE (Retired) - Power Systems
There are no UL listed 600V max. overcurrent protective devices that can be used with conductors sized per the 90?C column
 

Smart $

Esteemed Member
Location
Ohio
If I had intended to respond to your quote, I would have quoted you in my posting.
This response is directed to all participants...

Many visitors choose to view these forums in the "Linear" Display Mode. I do myself. However, aside from the OP, every post to the thread is in response to another. That post is the one in which you clicked the Quote or Reply button. Those that view these forums in "Hybrid" or "Threaded" Display Mode realize this.

PS: The Display mode can be changed via the "thread menu" at the upper right corner of the OP.
 
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There are at least two instances where a 90?C-rated conductor can be used at it's full ampacity rating. One such scenario is under 310.15(A)(2) Exception. The other is installations qualifying under 110.14(C)(2) for 600V and less. Only if identified otherwise is the any limitation for over 600V.

One debatedly practical application is to go from 75?C-rated size to 90?C-rated size conductor by joining circuit conductors in a terminal box with 90?C-rated terminations (i.e. terminal strips, splice blocks, etc.). Of course the enclosure itself also needs to be rated for 90?C or higher operationn.


I do not see either of the two sections you mentioned as being practicable for the daily work we see 99% of the time.
 

Smart $

Esteemed Member
Location
Ohio
I do not see either of the two sections you mentioned as being practicable for the daily work we see 99% of the time.
Perhaps... but it answers the question?in some small way?posed in the OP; the question that everyone seems to dance around because it is, in many, but not all instances, impracticable, as you say.
 
I did not post to deny your post. I see so many who think the 90C column is the way to size conductors, that I am surprised. I just wanted to let others who are not too sure to be careful when choosing which column for the final determination of ampacity of conductors.
 

Smart $

Esteemed Member
Location
Ohio
I did not post to deny your post. I see so many who think the 90C column is the way to size conductors, that I am surprised. I just wanted to let others who are not too sure to be careful when choosing which column for the final determination of ampacity of conductors.

I understand :)

While we're on the subject though, is there any code which says 310.15(A)(2) Exception cannot "trump" 110.14(C)(1)?
 

hardworkingstiff

Senior Member
Location
Wilmington, NC
This response is directed to all participants...

Many visitors choose to view these forums in the "Linear" Display Mode. I do myself. However, aside from the OP, every post to the thread is in response to another. That post is the one in which you clicked the Quote or Reply button. Those that view these forums in "Hybrid" or "Threaded" Display Mode realize this.

PS: The Display mode can be changed via the "thread menu" at the upper right corner of the OP.

Thanks Smart! I never noticed that before.
 

Smart $

Esteemed Member
Location
Ohio
I believe the Display mode can be changed from the top of any page.
AFAICT, the option is only available on any individual "thread" page (exactly where I stated it is). Other pages, such as reply and thread lists do not have a "thread menu". Changing it in one thread changes it for subsequent visits (and perhaps refreshes) to any other thread until viewer changes it back.
 
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LarryFine

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Electrical Contractor
Full moon?:roll:
Okie-dokie!
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