480 volt step down transformer question

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I need to run 2600ft. of underground single phase 100amp service to a rural shed and feedlot. The POCO will set a 480 volt single phase trans. at a minimal cost I would then step down the voltage at the load to 120/240 volts. Here is what I am proposing to do after doing the voltage drop calculations. Use AL 500kcmil with 350 neutral with a 25KVA step down transformer at the load. This being the first time I am doing this I am wondering if this will this work satisfactorily?
 
Your wire size seems Un necessarily large. Calculate your voltage drop at the actual expected load, not the full service size. I might go for more like 250 AL. Also, set up your wire run like the diagram shown in post 72. Corner ground the 480 and you only need two conductors:

http://forums.mikeholt.com/showthread.php?t=194062&page=8

Edit: corner ground isn't the correct term. Ground one leg of the 480 if you can. POCO might only provide it with a grounded center tap though.
 

infinity

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I need to run 2600ft. of underground single phase 100amp service to a rural shed and feedlot. The POCO will set a 480 volt single phase trans. at a minimal cost I would then step down the voltage at the load to 120/240 volts. Here is what I am proposing to do after doing the voltage drop calculations. Use AL 500kcmil with 350 neutral with a 25KVA step down transformer at the load. This being the first time I am doing this I am wondering if this will this work satisfactorily?

Sounds good to me but as EF stated your conductors are well oversized. What numbers did you use to figure the voltage drop? At 2500', 1Ø, 480 v, 40 amps I get 250 kcmil with less than 3% VD.
 
Sounds good to me but as EF stated your conductors are well oversized. What numbers did you use to figure the voltage drop? At 2500', 1Ø, 480 v, 40 amps I get 250 kcmil with less than 3% VD.
Okay I see where I have made a mistake. I am using Mike Holts voltage drop calculator and had my amps set at 100A. at 480 volt. Which should actually be 50A at 480. This would be correct right?

I am using Aluminum. I think your 1/0 wire size example is using copper is that correct?
 
Your wire size seems Un necessarily large. Calculate your voltage drop at the actual expected load, not the full service size. I might go for more like 250 AL. Also, set up your wire run like the diagram shown in post 72. Corner ground the 480 and you only need two conductors:

http://forums.mikeholt.com/showthread.php?t=194062&page=8

Edit: corner ground isn't the correct term. Ground one leg of the 480 if you can. POCO might only provide it with a grounded center tap though.
My calculated load would be less than 100 amps at this time but wanted to leave room for future expansion for small motor loads on grain bins and such. Maybe this is way overkill??

I had not thought of grounding one leg of the 480. I will talk to POCO about this.
 
Okay I see where I have made a mistake. I am using Mike Holts voltage drop calculator and had my amps set at 100A. at 480 volt. Which should actually be 50A at 480. This would be correct right?

I am using Aluminum. I think your 1/0 wire size example is using copper is that correct?
Nevermind my post about the 1/0 copper wire I see you said 250 kcmil AL.

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SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Ask the POCO if they will supply you with a 600V service instead of 480V. Since you are buying a step down transformer to put at the load anyway, see if they will give you a higher voltage service; you can downsize your conductors even further.



SceneryDriver
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
For that matter, I would inquire about the cost of having the utility power run all the way to the load. It might cost less than your feeder installation, and certainly be more electrically efficient.
 
For that matter, I would inquire about the cost of having the utility power run all the way to the load. It might cost less than your feeder installation, and certainly be more electrically efficient.

One utility near me allows customers to run their own primary, poco just supplies transformer and hooks it up. 15kv primary is only low $2's per foot. The other utility near me doesn't allow that and they charge big money like $12/ foot.
 
For that matter, I would inquire about the cost of having the utility power run all the way to the load. It might cost less than your feeder installation, and certainly be more electrically efficient.
The utility quoted $40,000 to run the line which would be overhead and along the road and ends up being 1 1/2 mile instead of taking a shortcut through the pasture.
I think I can do it for less than a half of that but, yes the owner will have to maintain.

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