# Stuck on NEC Chapter 9, table 8



## Electrical-EE (May 4, 2017)

I am doing voltage drop calculations. For my project, I need to do calculations for various temperatures. However, NEC table displays only the readings for 75 degrees. I am trying to do the calculations from R2 = R1 [1 + α (T2 − 75)]. Nonetheless have not got some appropriate results. Could somebody please illustrate this with 1 or 2 calculations? Even I am unable to reverify 2.01 for #12 AWG


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## MadSparky (Mar 2, 2018)

Electrical-EE said:


> I am doing voltage drop calculations. For my project, I need to do calculations for various temperatures. However, NEC table displays only the readings for 75 degrees. I am trying to do the calculations from R2 = R1 [1 + α (T2 − 75)]. Nonetheless have not got some appropriate results. Could somebody please illustrate this with 1 or 2 calculations? Even I am unable to reverify 2.01 for #12 AWG


What temperature are you referring to? Ambient? Conductor max operating? Termination? Also you don't use temperature typically in voltage drop calcs. You do that first and then apply adjustment factors.

Sent from my A574BL using Tapatalk


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## cabletie (Feb 12, 2011)

It looks like the correction factor for changing between 60, 75, and 90 degree C is 1.05. 

Depending if you are changing temperatures going up or down is weather you divide or multiply your 1.05 correction factor.


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## cabletie (Feb 12, 2011)

Here's a voltage drop example of going from 75 to 90 degree C.


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## Electrical-EE (May 4, 2017)

*Correction factor*



cabletie said:


> It looks like the correction factor for changing between 60, 75, and 90 degree C is 1.05.
> 
> Depending if you are changing temperatures going up or down is weather you divide or multiply your 1.05 correction factor.


Yeah I am trying to find the correction factor, but how does this correction factor varies? I think so 1.05 is not constant?


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## Electrical-EE (May 4, 2017)

*Title of book*



cabletie said:


> Here's a voltage drop example of going from 75 to 90 degree C.


Thanks,

May I know the title of Book?


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## Electrical-EE (May 4, 2017)

I am actually following this voltage drop formula calculation (http://www.electrical-formulas.com/voltage-drop-formula/)
...
Where at t = 75°
K = 12.9 for copper conductors
K = 21.2 for Aluminum Conductors
————————————-
For other temperatures use the equation
R2 = R1 [1 + α (T2 − 75)]
Where
αcu = 0.00323
αAL = 0.00330

In basic formula:
Vd = [2K * L * I] / CM

I am actually willing to know how does this K varies with temperature. (Feeling difficulty in above equations)How it came 1.05 to 90 degree. And how can we find it for other temperature let's say 20 degrees.


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## RePhase277 (Feb 5, 2008)

Look at the Neher-McGrath equation. This should get you where you want to go:

http://www.electrician2.com/ampacity.htm


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## Electrical-EE (May 4, 2017)

*It works*

Got it thanks for sharing.


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## telsa (May 22, 2015)

You just helped an EE.

Shame!


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## Bird dog (Oct 27, 2015)

telsa said:


> You just helped an EE.
> 
> Shame!


The OP would be more helped on Mike Holt's Forums, because, engineers are there.


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## RePhase277 (Feb 5, 2008)

Bird dog said:


> The OP would be more helped on Mike Holt's Forums, because, engineers are there.


No he wouldn't. He'd get a lot of talk and no real-world experience.


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