Help with load calculations

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gunter78911

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So i need some help with load calculations, trying to figure out this on my own, But..... life is so much easier when someone shows you how its done.

So my question is

Whats the current-carrying capacity for No.6 THWN aluminum conductors run through an ambient temperature of 38 Celcus ?
I'm looking at 300.15 right now, but i'm having a hard time making it out.
 
gunter78911 said:
...Whats the current-carrying capacity for No.6 THWN aluminum conductors run through an ambient temperature of 38 Celcus ?
Click to expand...
From 2011 Table 310.15(B)(16), THWN Al is under the column header 75?C. #6 is shown to have an allowable ampacity of 50A, for not more than 3 conductors, based on an amnient air temperature of 30?C.

Next, look at Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30?C (86?F). Correction factor for 38?C under the 75?C Temperature rating of conductor column is 0.88.

50A ? 0.88 = 44A

If you have more than 3 conductors, you would multiply that result by the appropriate percentage in Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable.
 
Voltage drop

Voltage drop

So whats the Voltage Drop for a 120V single-phase, two wire branch circuit, 100' long useing copper conductors of 6,530 circular mils with a noncontinuous load.

So under Chapter 9 table 8 6,530 is No#12 AWG. so what the formula to put this together?
 
Look at the resistance/impedance column in the table, divide it by 5 (200 feet of wire, table value is 1000 feet).
Find out load in amperes and apply Ohms law to get voltage drop.
Divide voltage drop by original voltage to get percentage.
 
gunter78911 said:
Sooooo...... 2 X 100' X 6.57 X 13A = 17,082 divided by 6530 = 2.61 ? :?
________
6530
Click to expand...
Not sure where you got the 6.57 value... or why you divided by 6530.

Jim (fmtjfw) gave you what I call the R.I.D method....

Ohms Law: E=IR

In this case E is voltage drop, so...

Vd=IR

We determine the value of R as

2D ? R/1000'

Where D is one-way distance (times 2 makes it the total circuit distance), and R/1000' is the Table resistance per 1000' value. So we now have (slightly rearranged)...

Vd=2?R/1000'?I?D

The downside of this (and some other methods) is that the resistance value given in the Table is at 75?C. In normal operating ambient, 13A through a #12 copper conductor will not raise its temperature to 75?C. Visit the link below and scroll to the calculator (the top portion explains a bit, but the math is a little complex)...

http://www.electrician2.com/calculators/vd_calculatoradv.htm
 
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