Chapter 9 Table 8 vs Table 9

[shespuzzling]

Hi,
Wondering if someone can explain why we are allowed to use Table 8 for single phase AC circuits (small wire and unity PF) but not 3 phase circuits.
Thanks

 

[charlie b]

Table 8 addresses single conductors, not single phase circuits. It gives us the DC resistance of a single conductor. It does not address reactance, the other factor that combined with resistance gives us the total impedance. I am not sure why not.

Table 9 takes into account the impact of the conduit type, the resistance, the reactance, and the power factor, and gives us the net reactance ("Z").

 

[shespuzzling]

Got it thanks. Related question re: Table 9. I understand how AC current in a conductor could induce eddy currents in steel conduit. How does this affect the reactance of the conductor as exhibited by the different reactance values for steel, PVC and aluminum conduit?