Sizing service entrance conductors

[eddie_kerri]

I am assisting a friend in the state of Kentucky with powering his pole barn with a new 200 amp service. The URD cable will be direct burial from the utility pole at the road to the pole barn 450 feet from the pole. I have conflicting information regarding the size of the URD to allow for the long distance. I have been told anywhere from 4/0 to parallel 600 MCM Aluminum. The truth lies somewhere in the middle. Please advise as to what URD direct burial aluminum conductor size is appropriate for this application. Please note I am not looking for alternate methods to complete the project. If this was your home and you were required to install URD direct burial aluminum cable to power a 200 amp panel, what size would you use based on the NEC.

Thanks,
Eddie

 

[kwired]

I am assisting a friend in the state of Kentucky with powering his pole barn with a new 200 amp service. The URD cable will be direct burial from the utility pole at the road to the pole barn 450 feet from the pole. I have conflicting information regarding the size of the URD to allow for the long distance. I have been told anywhere from 4/0 to parallel 600 MCM Aluminum. The truth lies somewhere in the middle. Please advise as to what URD direct burial aluminum conductor size is appropriate for this application. Please note I am not looking for alternate methods to complete the project. If this was your home and you were required to install URD direct burial aluminum cable to power a 200 amp panel, what size would you use based on the NEC.

Thanks,
Eddie

Based on NEC only - any conductor with an ampacity over 175 amps can be protected by a 200 amp overcurrent device - as long as the calculated load on that conductor is not more then the ampacity of the conductor. What does that mean? Most of the time it means you can use 4/0 aluminum conductor with an ampacity of 180 amps as long as you don't have 181 to 200 amps of load.

Why might you need larger conductors? Voltage drop. How much larger depends on what the actual load is and how much voltage drop you want to tolerate. There is no code requirement voltage drop (as a general rule) - just an informational note with a suggestion.

 

[Smart $]

What kind of loads does your friend plan to supply in this pole barn? Figuring the minimum conductor size for voltage drop is dependent on the peak draw value one uses for the calculation.

 

[kwired]

And if you are running a 200 amp line just because "noboby runs less then 200 amps anymore" concept, but only have say 65 amps maximum load, you already have a jump start on voltage drop issues.