#### Crohnos01

##### Member

- Location
- BG, Washington

I just found this forum...Very nice and I plan on hanging out a lot!

It's been awhile since I have done any VD calcs, and inductive 3 phase circuits even longer still so pardon my rust. I initially did a calculation using a negligible inductance calc vd = (1.73*K*L*I)/Cm found in Ugly's and then realized that since I was working on a 3 phase circuit with a motor hanging on the end of it, I should really be including the motor PF in the calculation. Using the figures in Table 9 of the NEC code, I came up with a line to line VD of 2.37 volts vs. my original calculation of 2.7 volts. (I pulled a .69 ohm/ft figure from the table). In either case, I am just over a 1% VD and should be good to go....However.... Shouldn't the calculation including the motor PF provide a higher VD rather than a lower one? Granted it's not much, and it matters not in the grand scheme of things, but I am struggling with the "why" Did I go bug-eyed and miss something?

Specifics of the circuit in question:

Motor HP = 15

3 phase

208 volt

Length = 50 ft.

Amps = 39.59 (I rounded to 40)

Wire size = #8 THHW Cu

KW = 11.2 @ FLA

I am planning on running in PVC conduit buried and used the standard 75 deg C. Could someone check my math?

Thanks,