310.15b16. Voltage drop/terminal ratings

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Danny89

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Can someone explain the answer to this example with code tables and notes. Formula for voltage drop is three phase

Chapter 9 table 8 is where u get the circular mils size for wire. Cooper think wire is to be used.

Terminal ratings are 75 degrees Celsius.

3 hots 1 ground needed 100amp load. 500feet away. What size wire is needed?
Thanks in advance

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Sounds like a home work question (without enough information) so take a shot at it and give us your answer first.

Roger
 
WarrMann said:
Voltage is missing. (Both from the question, and the far end of the wire)

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The actual voltage drop wold be the same regardless. Obviously the % drop would change.
 
augie47 said:
The actual voltage drop wold be the same regardless. Obviously the % drop would change.
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Which effects the size of the conductor. He's looking for a wire size. I was taught to look at the starting voltage when using a voltage drop formula to size wires.

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WarrMann said:
Which effects the size of the conductor. He's looking for a wire size. I was taught to look at the starting voltage when using a voltage drop formula to size wires.

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my apology.. when I read it I thought he was just looking for the voltage drop.
 
augie47 said:
my apology...
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Whew...lol. i thought for a second there i was going to have yet another guy on this forum tell me the way i do things is wrong.

I hope the OP gives us the info we want so everyone can chime in with how they would go about sizing this one.

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Well, he said 3 phase, 100 amps... so that starts around what, number 2... copper thhn is what I am assuming cooper think means but...of course, now you have the three conductors in a tray or such so you have derating and the 500 feet with 75 degree connections....2/0?.
 
Adamjamma said:
Well, he said 3 phase, 100 amps... so that starts around what, number 2... copper thhn is what I am assuming cooper think means but...of course, now you have the three conductors in a tray or such so you have derating and the 500 feet with 75 degree connections....2/0?.
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If only 3 conductors there is no adjustment necessary. 3AWG is good for 100 amps 75C.

What is not real clear is if the load is 100 amps or if it a 100 amp feeder with a lesser load on it, as well as what is continuous, what is non continuous for load. Once one knows absolute minimum conductor needed then comes how much voltage drop is acceptable and can the minimum ampacity conductor provide that or not.
 
Question is...
100a load not continuous. 75 degrees Celsius terminal ratings. 3 phase 480volt supply. 450 feet distance. What size wire should be used?

Answer is:
1.732x12.9x100x450/14.4=69,821.25 cmils

Chapter 9 table 8 ...#1 awg will work ...83,690 cmils. Copper

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Danny89 said:
Question is...
100a load not continuous. 75 degrees Celsius terminal ratings. 3 phase 480volt supply. 450 feet distance. What size wire should be used?

Answer is:
1.732x12.9x100x450/14.4=69,821.25 cmils

Chapter 9 table 8 ...#1 awg will work ...83,690 cmils. Copper

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Click to expand...
You didn't mention acceptable voltage drop in the question, but apparently is 14.4 volts.
 
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