Voltage drop and Transformer calculations

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zcanyonboltz

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I'm studying to take the master electrician exam already hold my RW and journeyman it's been awhile since I've done voltage drop calculations and Transformer are there examples in Annex d or chapter 9 examples of voltage drop and or Transformer calculations just something I can refer to when taking the exam so I don't have to study for it that hard I know there's only a total of 2 questions each on the exam thank you
 
I've been studying this a bit can anyone tell me where the 12.9 ohms value for K copper and the 21.20 ohms value for K aluminum come from are those values in the NEC? Thanks
 
zcanyonboltz said:
I've been studying this a bit can anyone tell me where the 12.9 ohms value for K copper and the 21.20 ohms value for K aluminum come from.
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They are physical properties of the metals and I believe they were derived via experimentation.

 
Thank you it's pretty simple just been a long time since I was in first year apprenticeship school easier to just learn how to do rather than having to look for an example which I haven't found in chapter 9 or the annex
2xKxIxD÷VD I just couldn't remember where K came from but it all the textbook examples I found those numbers are staying constant thank you
 
FWIW, if you look at Table 8 in Chapter 9 at ohms per k ft for 1000 kcmil AL & Cu you will find those numbers.
 
zcanyonboltz said:
I'm studying to take the master electrician exam already hold my RW and journeyman it's been awhile since I've done voltage drop calculations and Transformer are there examples in Annex d or chapter 9 examples of voltage drop and or Transformer calculations just something I can refer to when taking the exam so I don't have to study for it that hard I know there's only a total of 2 questions each on the exam thank you
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Hey remember this. 75 is passing. Once you pass, it will never matter that someone else whatever. EVERY calculation question takes time and there is always a higher risk that you will make a math error. So, set those aside and also set aside those questions that you can't locate quickly in the code book. Do those last.
 
zcanyonboltz said:
So if I'm given a question does the value for K stay at 12.90 ohms for copper and 21.20 ohms for aluminum or can those values change?
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I believe those numbers are based on a conductor temperature of 75°C. That is also the temperature the values in the Chapter 9 tables are based on.
 
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