480 volt/ 200amp 300ft from main

[Dolfan]

Good Sunday morning to all of you out there. I am just double checking my calculation for wire size on a 200amp 480v 3phase panel 300ft from the Main. I got 250's, is that correct, that's going to be a pain to pull in. Please tell me I'm wrong. Thanks in advance

 

[ggunn]

Good Sunday morning to all of you out there. I am just double checking my calculation for wire size on a 200amp 480v 3phase panel 300ft from the Main. I got 250's, is that correct, that's going to be a bitch to pull in. Please tell me I'm wrong. Thanks in advance

250 kcmil Cu with 1.32% Vd for 200A and 480V is what I get as well. Parallel sets?

 

[Dolfan]

3/0 would give me 472V, according to the calculator, that's even if I have 480 at the main. I'm just looking for a discount double check. :lol:

 

[ggunn]

3/0 would give me 472V, according to the calculator, that's even if I have 480 at the main. I'm just looking for a discount double check. :lol:

But what is the correctly derated ampacity of that 3/0? Voltage drop is not the only limiting factor. Have you considered pulling parallel sets?

 

[Dolfan]

But what is the correctly derated ampacity of that 3/0? Voltage drop is not the only limiting factor. Have you considered pulling parallel sets?

have not even considered that, why would I need to?

 

[Carultch]

Good Sunday morning to all of you out there. I am just double checking my calculation for wire size on a 200amp 480v 3phase panel 300ft from the Main. I got 250's, is that correct, that's going to be a bitch to pull in. Please tell me I'm wrong. Thanks in advance

Can you be specific about what the 200A refers to? OCPD? Continuous load? Non-continuous load? The 125% / 100% mix of continuous and non-continuous loads? Ampacity is calculated with a safety factor on the continuous loads, while voltage drop is calculated directly from the loads without this factor.

A single set of 3/0 Copper is the minimum local size (as in, minimum size for ampacity considerations only) for the 200A circuit, if we are talking about 200A of OCPD.

Assuming we are also talking about 200A of noncontinuous loads that size this OCPD, I'd also use that number in the voltage drop calculation.
%Vd = L*sqrt(3)*I*r/(1000*V)

L=300 ft
I = 200A
V = 480V, when we use the sqrt(3) factor upstairs

Here's my source of r:
https://www.anixter.com/content/dam/Anixter/Guide/7H0011X0_W&C_Tech_Handbook_Sec_07.pdf

For 3/0, r=0.0799 ohm/kft. AC circuit/multiconductor in metal at 75C. And Vd = 1.73%, which meets the NEC recommendations.

It does also depend on how much voltage drop "budget" you want to reserve for other parts of the circuit. If there are other feeders leading up to the source, you might want to reduce it so that the total of all feeders is less than 3%. Or even 2%, if the branch circuits are already at 3%.

 

[Carultch]

have not even considered that, why would I need to?

Parallel sets can be strategic, because two small conductors in parallel have more ampacity per KCMIL of conductor, even if they are in the same conduit. And they are easier to pull. The minimum size you can use for paralleling is 1/0.

For instance, a 400A circuit can use a single 600 kcmil Cu, or it can be parallel 4/0 Cu in the same conduit. Parallel 4/0's has only 424 kcmil of total conductor, so that's about 30% less copper you don't have to buy.

When voltage drop is a concern, you should expect about the same total KCMIL of conductor no matter what the paralleling arrangement. There is a very slight advantage to paralleling with AC circuits, because 2 smaller conductors have less AC-specific resistance than 1 large conductor of the same total KCMIL. Again, this is only a slight advantage, and it isn't an advantage for DC. In any case, you should still expect nearly the same amount of total KCMIL, when curtailing voltage drop is important.

DC resistance per length is inversely proportional to KCMIL, with no other factors. AC resistance in 1/0 and larger wires deviates from this trend, due to inductance factors and the "skin effect". AC resistance is also a function of whether you have a ferrous raceway (RMC, IMC, EMT, Steel LFMC), or a non-ferrous raceway (Aluminum RMC, Aluminum LFMC, Stainless, PVC, LFNC, HDPE).
http://i.ytimg.com/vi/DixBEjsiDRw/hqdefault.jpg

 

[Dolfan]

Which is why I don't like engineering a job like this. It's a huge window factory with all types of machinery. I don't believe that I have any continuous loads, but who knows what they may have there house electrician tie into this run. We are also adding a 480/240 transformer along with a panel, if I decide to do it, which may not happen because of other jobs that are more lucrative.