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Sizing Conductors for <3% Voltage Drop; the 'K' value

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Hello everyone,


Here, I'm using the circular mills method as opposed to the resistive method:

To find the Voltage Drop of a single-phase ckt. I'd use: VD=2*R*L*I/CM

In order to size a conductor properly while staying within the 3% voltage drop recommendations I'd use: CM=2*K*L*I/VD

VD=voltage drop

L=length of conductor in ft.;one-way

CM=circular mills from Chap.9, Table 8

I=load current

R=the resistive value from Chap.9,Table 8 or 9

K=The D/C constant for the resistance of a 1000-mill conductor that's 1000 ft. long at 75 degrees C.


My question is with the K value. I've seen four different sets of values noted. The values are different for copper and aluminum.

The two sets that seem most accurate are:







An electrician on a different forum stated that he uses cu-7 & alu-11. I'm not too sure about that.

I've been using the first set thinking that keeping the value slightly higher is playing it safe.


Any takers on this one?



I'd appreciate it



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