table 8 ?

[hcecabigdog]

i was showing my class a voltage drop calc last night and had them try one. the calc i showed them gave you the wire size you need for the answer. you go to table 8 and use the cmil column to find the size you need. one student had a different answer than everyone else. he said he used note 4 at the bottom. it talks about the ICSA and i'm assuming it is reffering to the dc resistance side of the table. any thoughts.
thanks

 

[dpenbert]

Re: table 8 ?

The IACS (International Annealed Copper Standard) conductivities used is already factored into the numbers listed in the table.
The calculation I use is CM = 2*K*I*D / VD (Single Phase). The IACS conductivity is factored into the K (resistivity) value. (Conductivity is 1/resistivity). I believe the approximate K(75C) is equal to 12.9 ohms CU.
So I think your assumption is correct that the IACS value refers to the Direct-Current Resistance side of the table, and we should assume 100% IACS is being used for the table values.
Someone correct me if I am wrong, but this is what I think.

David

 

[jtester]

Re: table 8 ?

...bigdog
If you are using dc examples Table 8 is OK. If you are doing AC examples Table 9 is more accurate because it lists AC resistance where Table 8 is DC. In fact, I use the effective Z columns which include reactance as well as resistance. This is an even more accurate calculation, particularly with larger wire sizes.
Jim T

 

[radiopet]

Re: table 8 ?

Table 8 or Table 9 really does not matter until you get over 1/0 anyway. Notice the resistance is no difference until you get to that point and should not make a real difference in the calculation again unless you are going larger than 1/0 in size.