We are wiring a 2300sq.ft. home and are installing 200amp service. The distance from the meter base to the pole is 250' and the distance from the meter base to the panel is 40'. We have approx. the load at 160 amps and will be installing 3-3/0 thhn cu conductors in 2" schedule 80 pvc. We have calculated the VD at 7.18 which is 2.99%. We also will be installing a 100 amp sub panel in a barn at 70' with a load of approx. 50 amps with 3-#6 thhn cu conductors in 1.25" pvc schedule 80. We have calculated the VD at 3.43 which is 2.86%. Are we correct in our calculations?
service size
- Thread starter elecon
- Start date
- Status
- Location
- Massachusetts
Re: service size
For the main panel I come out very close to your figures.
For the sub panel I come out with 1.42% VD, not 2.86% I think you may have used 120 volts as the starting point for your percentage.
For the main panel I come out very close to your figures.
For the sub panel I come out with 1.42% VD, not 2.86% I think you may have used 120 volts as the starting point for your percentage.
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: service size
My calculations show a difference, maybe because I used "Z", impedance, instead of resistance. I recommend using Table 9 in the NEC, and using the column titled "Effective Z at .85 PF for Uncoated Copper wire". From that column you see that 3/0 in PVC has an impedance of .088 ohms/1000 ft.
160 amps X (.088/1000) X 290' X 2 = 8.166 volts
8.166/240 = 3.42% drop
similarly for the #6 circuit, you have 3.08 volts drop or 1.28%
My calculations show a difference, maybe because I used "Z", impedance, instead of resistance. I recommend using Table 9 in the NEC, and using the column titled "Effective Z at .85 PF for Uncoated Copper wire". From that column you see that 3/0 in PVC has an impedance of .088 ohms/1000 ft.
160 amps X (.088/1000) X 290' X 2 = 8.166 volts
8.166/240 = 3.42% drop
similarly for the #6 circuit, you have 3.08 volts drop or 1.28%
- Location
- Massachusetts
Re: service size
I use a software program on my PC for VD and while it does not consider power factor I can choose steel or PVC raceways.
When I did my calculations I left it set on steel, when I run the same figures using PVC raceway I come out with even less VD.
Steel 3.05% VD
PVC 2.97% VD
I use a software program on my PC for VD and while it does not consider power factor I can choose steel or PVC raceways.
When I did my calculations I left it set on steel, when I run the same figures using PVC raceway I come out with even less VD.
Steel 3.05% VD
PVC 2.97% VD
john m. caloggero
Senior Member
Re: service size
Based on the a single-phase voltage drop program I have on my computer, based on a distance of 250' + 40'= 290' with a load of 160 amps, PF 0.85, 3/0 CU conductor in PVC: the VD is 8.097 volts and 3.374%. The VD drop for the 70' run, #6 CU, with a load of 50 Amps. the VD is 3.11 and 1.296%.
Based on the a single-phase voltage drop program I have on my computer, based on a distance of 250' + 40'= 290' with a load of 160 amps, PF 0.85, 3/0 CU conductor in PVC: the VD is 8.097 volts and 3.374%. The VD drop for the 70' run, #6 CU, with a load of 50 Amps. the VD is 3.11 and 1.296%.
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