NEC Voltage Drop Calcs & Power Factor

[shespuzzling]

Been putting together a voltage drop calculation spreadsheet based on the NEC tables and noticed something surprising. I though that the voltage drop in a circuit would always increase with decreasing power factor. That tends to be the case with larger wire sizes (3/0 and above) but is definitely not the case with smaller wires. These calculations were based on Chapter 9 Table 9, I could show my work if you want but taking the following parameters, the voltage drop is worst with unity pF:

A=50A
wire size=8awg
length=50
voltage=120
phase=1

Here are the percent voltage drops I got starting with pf=1, then .9, .8, .7, .6 ,......,.2

pf=1 - 3.24%
3.04%
2.76%
2.47%
2.17%
1.86%
1.55%
1.23%
pf=0.2 - 0.92%

This happens for all the wires up to 2/0. What gives? Is it just due to the impedances of smaller wires?

 

[ramsy]

..I though that the voltage drop in a circuit would always increase with decreasing power factor..

My Tbl-9 calculator followed your results also - for purely resistive loads only. Very interesting, perhaps the engineers can explain this?

However, for inductive-motor loads adjusted per NEC 220.18(A), both Current and Voltage Drop increase with decreasing Power Factor, inversely proportional, as expected.

 

[shespuzzling]

any thoughts?

 

[ramsy]

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