Nbmarlar78
Member
- Location
- Jackson, WY
I am feeding a 200 amp subpanel from an MDP. The subpanel is located approximately 350 feet away. What size THHN wire should I use when considering voltage drop? I have a 4” pvc in place.
Feeder size/voltage drop
- Thread starter Nbmarlar78
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The size of the sub panel is not really relevant, what is the actual load to be served?
Roger
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Making some assumptions, and using the Southwire web calculator https://www.southwire.com/support/voltage-drop-calculator.htm
1 conductor per phase utilizing a #350 Copper conductor will limit the voltage drop to 2.79% or less when supplying 160.0 amps for 350 feet on a 208 volt system.
If you know the actual load rather than guessing at 80% of the panel rating, that is what you would use.
1 conductor per phase utilizing a #350 Copper conductor will limit the voltage drop to 2.79% or less when supplying 160.0 amps for 350 feet on a 208 volt system.
If you know the actual load rather than guessing at 80% of the panel rating, that is what you would use.
Nbmarlar78
Member
- Location
- Jackson, WY
Engineer wants it based on 80% for possible future equipment.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
he should be sizing it then.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I hope you're thinking of using THHN/THWN assuming when you say PVC; it is going to be below grade.
Bob is right, if an engineer is involved he should have sized it.
You could also run 500KCMIL aluminum, check pricing as it might be cheaper.
Knightryder12
Senior Member
- Location
- Clearwater, FL - USA
- Occupation
- Sr. Electrical Designer/Project Manager
According to my VD calculator, 1 set of 350KCMIL AL would limit the VD at 2.36%. 300 AL would be 2.75%. 4/0 CU would be 2.38%
using 208/3, 160 A and 3%
R from nec table in Ohm/1000'
0.03 x 208 = sqrt3 x 350/1000 x R x 160
R = 0.0643 Ohm/1000'
need selected conductor R to be lower
Cu 300 0.059 (250 is 0.066, close, 3.08%)
Al 500 0.057 (400 is 0.066, 3.08%)
imo go with the 300 Cu or 500 Al since the R values are based on 0.85 pf, which may be low
R from nec table in Ohm/1000'
0.03 x 208 = sqrt3 x 350/1000 x R x 160
R = 0.0643 Ohm/1000'
need selected conductor R to be lower
Cu 300 0.059 (250 is 0.066, close, 3.08%)
Al 500 0.057 (400 is 0.066, 3.08%)
imo go with the 300 Cu or 500 Al since the R values are based on 0.85 pf, which may be low
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
I would bet (2) 1/0 AL would be your least expensive option.
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