Sizing a Cable

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xCod3m4nx

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I'm running a cable out to a double wide trailer to supply it power. The main breaker will be 200 Amps and is 780ft from the trailer. We will be using CLX cable. The voltage is 120/240V. I used Voltage Drop = (2 x K x I x Distance)/CM . With K = 12.9 ohms for copper, I = 200Amps, Distance = 780ft, and CM = 600,000 for 600 KCmil. So I got VD = 6.71; therefore 6.71V/240V x 100% = 2.8% voltage drop. The biggest wire the wiring company we go with offers is 750 KCmil. Since it is 120/240V it's single conductor? I'm not to sure on this since I haven't had any experience sizing wires or using the NEC since I just graduated college.

Not to sure on how the parallelling wires works either. For this case if I had 3 - 4/0 AWG single conductors in parallel running out there would it work and would it be cheaper than a 750 KCmil? The code says 1-3 and you don't have to adjust the value. So my allowable amps for my breaker would be 3 x 260A = 780A for my breaker using table 310.16, 90C, Copper, XHHW-2. Which seems high but the Voltage Drop calculation would be = (2 x 12.9 ohms x 200A/3 x 780ft)/211600 = 6.34 Volts. Then 6.34V/240V x 100% = 2.64% VD. Is any of this correct or am I way off?
 
you can only use the 90 degree column for derating, not for sizing feeders. parallel may be cheaper, but you should get prices since there may be more labor and a wash. (you didn't mention what kind of raceways)
 
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Did you do a load calculation? 200 amps seems too high for a trailer?
600 kcm 75C from table 310.16 ampacity is 420 amps. The voltage drop looks correct. 2 ckts of 3/0 is 200 x 2 = 400 amps. The voltage drop is about the same as the 600 kcm. You can not use the 90C rating of the conductor for ampacity. You will have to determine the cheapest method of service.
This is an online VD calculator for your use http://www.electrician2.com/vd_calculator.htm
 
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nakulak - I'll try to figure out what cost of labor is. The cable will be buried.

bob - loads are two 10KW (230/208V,single phase,60Hz) AC units, printer, up to 6 PC + monitor, lights, coffee pot, microwave, mini fridge, well pump, other loads receptacles (just a guess of what we think).

So I'm thinking running Amps would be: 41.7A x 2 (for AC units) + .42A (printer that uses 100W) + 6 x 1.45A (350W PC + Monitor) + 15A (lighting: double wide trailer usually 16ft x 75ft = 1200sq ft x 3VA/sq ft = 3600VA/240V) + 5A (1200W coffee pot) + 5A(1200W microwave) + 2.5A (600W fridge) + 4.9A (1/2hp well pump) + 15A (extra loads) = 139.92A

Starting Amps: 58A x 2 + .42A + 6 x 1.45A + 15A + 5A + 5A + 2.5A + 6.125A + 15A = 173.75A

Thanks for the VD calculator :grin:
 
Can I use Table 310.15(B)(6) since the double wide trailer will be used as a work area? Says for 200A it would be Copper 2/0 but does that take in to account VD for 780ft?
 
xCod3m4nx said:
Can I use Table 310.15(B)(6) since the double wide trailer will be used as a work area? Says for 200A it would be Copper 2/0 but does that take in to account VD for 780ft?
Click to expand...

the values in this table are for dwelling unit feeders or services, if your application is not a dwelling unit you can not use this table.

If you can use the table it still does not consider possible voltage drop, it is just the minimum size conductor permitted larger conductors may be desired or required for other reasons.
 
xCod3m4nx said:
Can I use Table 310.15(B)(6) since the double wide trailer will be used as a work area? Says for 200A it would be Copper 2/0 but does that take in to account VD for 780ft?
Click to expand...

Even without VD I can tell you off the top of my head that 200A is usually a 3/0 copper. Are you still using the 90 c column?
Also you do still need to account for that 780ft VD......
 
jumper - good catch. 110.14(C) does say that I should use 60c or 75c unless I make the correct ampacity adjustments. So I guess I'll size for 75c.

Question on conductors for the wire. If it was a 3 phase, 480V line I would be using say a 600KCmil 3/C wire but since it is a single phase 120/240V line would I be using a 600KCmil 1/C? Also for parellelling and accounting for the VD. If I have two 1/0 AWG rated at 75c, 3/C. This would give me 300 allowable amps x 80% (for 4-6 conductors in parallel) = 240A. Then my VD calculation would be: (2 x 12.9ohm x 200A/6 conductors x 780ft) / 105600(CM for 1/0) = 6.35V or 6.35V/240V x 100% = 2.65% VD. Is that correct or did I do the 6 conductor thing wrong?
 
xCod3m4nx said:
daleuger - yes, still using the 90c column since the CLX cable we are looking at from okonite is rated at 90c
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If you are within the scope of the NEC on this work then I would look at your CLX cable. I do not see it listed in article 310 as a type listed for use.

Perhaps that's a cable the poco uses but it is not listed as a conductor for use under the NEC.
 
Let's not forget art. 550.32. A disconnect is needed no more than 30 feet from the trailer. Sorry, you probably know this but I want to make sure it doesn't get overlooked.
 
Dennis Alwon said:
If you are within the scope of the NEC on this work then I would look at your CLX cable. I do not see it listed in article 310 as a type listed for use.

Perhaps that's a cable the poco uses but it is not listed as a conductor for use under the NEC.
Click to expand...

CLX is an Okonite brand Type MC cable.
 
xCod3m4nx said:
...

Question on conductors for the wire. If it was a 3 phase, 480V line I would be using say a 600KCmil 3/C wire but since it is a single phase 120/240V line would I be using a 600KCmil 1/C? ...
Click to expand...
Properly written it is a 120/240 1? 3W system... the 3W meaning three wires, aka current carrying conductors.

Also, if you are under the 2008 NEC, you will have to properly ground your system at the disconnect and run an EGC between the disconnect and trailer.

The above means, if you use one cable, it will have to be 3C w/GRD.
 
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xCod3m4nx said:
... I would be using say a 600KCmil 3/C wire but since it is a single phase 120/240V line would I be using a 600KCmil 1/C? Also for parellelling and accounting for the VD. ...
Click to expand...
By my calculations, you only need to run 3C, 350kcmil copper for less than 3% VD.

Go to this calculator (scroll down) and enter the following parameters:
  • Copper
  • 350kcmil
  • 240 Volts 1-phase
  • 20C
  • 780 (feet)
  • 140 (amperes)
...and Click to Calculate button.
 
Sizing a Conductor

Sizing a Conductor

Can you get the local power company to run a line to a service panel at the trailer.
Then you will only need to worry about connecting your service to the inside panelboard per NEC 550.32 and 550.33.
 
xCod3m4nx said:
Smart$ - Thanks. I see what you're saying with the wiring. Used the calculator also and saw how you got 350KCmil to work.
Click to expand...

In your original post you used K = 12.9. When Smart$ changed the temp to 20C , K = 10.5. He also reduced the amperage to 140 amps. You may want to try this in your original calculation and see how close your are. Nothing wrong with the changes. They may actually represent a more correct scenario.
 
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