Voltage drop calculator

[ggunn]

At this site http://www.nooutage.com/vdrop.htm there is a voltage drop calculator, but what I am seeing there is confusing me.

For a three phase 480VAC run of 470 feet and a current of 163A, it tells me that for a double run of 4/0 Cu in steel conduit, I get a 1% Vd, but for a single run I can't get down to 1% even with the maximum conductor size of 750. Does this make sense? From Table 9, 4/0 Cu has a resistance of 0.207 ohms/1000'. To get to half that resistance I only have to go to 500.

Am I missing something?

 

[bob]

My calculator - PF = 1.0 RGS conduit shows

2 - 4/0 - 0.88%
1 - 4/0 - 1.75%
1 - 500 - 0.81%
1 - 750 - 0.59%

For PF = 0.80

2 - 4/0 - 1.12%
1 - 4/0 - 2.24%
1 - 500 - 1.44%
1 - 750 - 1.26%

Checked your calculator. I think it is making an error.

 

[david luchini]

I suspect that they're using Effective Z at a certain power factor, rather than simple resistance. Using the Effective Z numbers from table 9, parallel 4/0 would have a smaller Z than single 750's.

Edit: Bob types faster than me

 

[ggunn]

My calculator - PF = 1.0 RGS conduit shows

2 - 4/0 - 0.88%
1 - 4/0 - 1.75%
1 - 500 - 0.81%
1 - 750 - 0.59%

For PF = 0.80

2 - 4/0 - 1.12%
1 - 4/0 - 2.24%
1 - 500 - 1.44%
1 - 750 - 1.26%

Which calculator is that? I have looked at these three:

http://www.electriciancalculators.com/calculators/vdpfcalculator_initial.html
http://www.nooutage.com/vdrop.htm
http://www.powerstream.com/Wire_Size.htm

and no two of them agree.

BTW, this an inverter feed to an interconnect and the PF is >0.95.

 

[ggunn]

I suspect that they're using Effective Z at a certain power factor, rather than simple resistance. Using the Effective Z numbers from table 9, parallel 4/0 would have a smaller Z than single 750's.

Edit: Bob types faster than me

All three of them claim to be using Table 9.

 

[Smart $]

All three of them claim to be using Table 9.

It appears only the first linked one has an entry for power factor. The other two must either be using resistance only or an assumed power factor.

 

[ggunn]

It appears only the first linked one has an entry for power factor. The other two must either be using resistance only or an assumed power factor.

But no two of them agree on the wire size for a single run. Weirder still is that all three agree that a double run of 4/0 would do the trick.

 

[Smart $]

But no two of them agree on the wire size for a single run. Weirder still is that all three agree that a double run of 4/0 would do the trick.

Well ultimately it comes down to which one, if any, agrees with you...