Chapter nine table 9

[terille]

In chapter 9 table 9 there are two listings for each awg. I have always used the bottom one but am not sure what use the top numbers have. Can anyone clear this up?

 

[starbright28]

The only thing that I can see is what the table is saying at the very top

The top number corresponds to the ohms to neutral per KILOMETER

and the bottom number corresponds to the ohms to neutral per 1000 FEET.

That is the only different with the number. One for metric, one for standard.

anyone can correct me wrong if I am not saying this right.

 

[charlie b]

You have it right, Amanda.

 

[terille]

Thanks

Thanks

Thanks for the help. I was assuming that the top was for something else.

 

[ryan_618]

Why would you use Table 9? Table nine only applies to the parameters given at the bottom, and provides no means of correction like Table 8 does.

 

[Smart $]

Why would you use Table 9? Table nine only applies to the parameters given at the bottom, and provides no means of correction like Table 8 does.

For one, Table 8 provides DC resistance values, whereas Table 9 provides AC resistance and reactance values for 3 conductors in [3 types of] conduit. Just on the headers alone, which is more appropriate for AC?

Note 1 of Table 8 specifies, in part, "These resistance values are valid only for the parameters as given." The bold emphasis is as printed, not added by me. Therefore, if the resistance values provided are for DC only, where is the means of correction to adjust for AC? (Answer: None is provided.)

Note 2 of Table 8 provides a formula to correct resistance for temperature changes. While it is not stated in either Table 8 or 9, I believe the formula can also be used to adjust values provided in Table 9.

 

[Rockyd]

I believe the formula being looked at is for voltage drop, and goes like this

3 Phase = 1.732 x K x I x D x Q
CM​

Q is the skin effect factor normally not used on conductors smaller than 2/0.

Q is derived by taking the AC resistance from table 9 chapter 9, and dividing it by the DC resistance from table 8 chapter 9.

I'm sure some heavy hitters can swing by and enlighten us more on the table, but that's all I can give you on it's primary purpose for me.

edit math error...it's fixxed now.