[FONT=times new roman said:
charlie b;[/FONT]1771926]
I don�t understand your concept of �desired temperature.� Let�s run through an example.
You start with a tabulated ampacity that was based on an ambient temperature of 30C. For your application, you are told that the actual ambient temperature will be 42C. You plan to use 90C rated wire, #6 THHN. There are two ways to find the ampacity.
Method 1:
� The 90C rating of #6 THHN is 75 amps.
� Table 310.15(B)(2)(a) gives a correction factor of 0.87.
� Multiply 75 times 0.87, and you get 65.3 amps
� We take note that 65.3 is higher than the 75C rating of #6 THHN (i.e., 65 amps).
� Conclusion: the ampacity is 65.
Method 2:
� The 90C rating of #6 THHN is 75 amps.
� Subtract 90 � 42, and you get 48.
� Subtract 90 � 30, and you get 60.
� Divide 48 / 60, and you get 0.8.
� Take the square root of 0.8, and you get 0.89.
� Multiply 75 amps times 0.89, and you get 67.
� We take note that 67 is higher than the 75C rating of #6 THHN (i.e., 65 amps).
� Conclusion: 65 is still the ampacity.
I suspect that there will be very few real life examples in which the use of the formula changes the ampacity in our favor.
this is an example in a closed thread and i'd like to build my question upon it
1- when the load is given in amperes
and it is as above 75 A, and i wanna choose the suitable AWG according to the same circumstances above
derating at 42 ambient c will be 65.3 A but the load needs to pass 75 A through this conductor so the wire amp have to corrected as =75/0.87=86.2A
so from the table the suitable conductor is 4 AWG which can carry 95 A. is that right ?
2- i didn't get 310.15 (A)(2), so for this example above if there are two ambient temperature along the conductor length 30 ,42 c
and the load still needs to pass 75 A through this conductor ,so i have to ampacities 75 A ,and 86.2A ,6AWG and 4AWG respectively .and the load is the essential controller factor it needs 75A It is its rating which would pass through the conductor if the ambient temp is 30 c regardless other adjustment factors
so According to this rule which AWG is the correct one ?
