# NEC Table 9



## cruzy (Oct 26, 2010)

For NEC Table 9 for impedance values, why do they give the ohms/neutral? what does the neutral have to do with the impedance of a phase line? And what if it is a 3 wire system with no neutral? Also, to use the table for voltage drop calcs, what pf do you use to calculate the effective Z, is it just the load pf?

Thanks


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## LMAO (Oct 26, 2010)

cruzy said:


> For NEC Table 9 for impedance values, why do they give the ohms/neutral? what does the neutral have to do with the impedance of a phase line? And what if it is a 3 wire system with no neutral? Also, to use the table for voltage drop calcs, what pf do you use to calculate the effective Z, is it just the load pf?
> Thanks


it is just the per phase impedance; don't get caught up in their terminology. Calculating three phase is just like the single phase except that you should pay attention to squared of three factor. Also, if it is single phase you need to multiply the distance of equipment to source by 2 to find the total cable length (you don't do that if you are calculating three phase voltage drop).

There is only ONE pf; and it will be given (it is the phase difference between voltage and current). The angle of Z is not pf.


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