480/240 Ranch Application

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meltedfire

New User
Location
Bastrop County, Texas
Occupation
Utility Engineer
Hi all,

New to the forum although have been lurking as a reader for some time.

A friend of mine asked me to help design a power distribution system for his 40 acre ranch. He doesn't want to put Poco poles all over the place and wants to keep a single handoff from the POCO if possible. Being a DC buy, I naturally started to think 480/240 system so that I can step him down as necessary for loads at different places in the property. This is all single phase - there is no 3phase available at the property. In essence, he wants an on-property intermediate voltage system to drop off to different locations as necessary.

POCO indicates to us that we can have single phase up to 800amp@120v services (100Kva transformer) and they are able to hand us 480V at 200amp (single phase - 2x 240v legs instead of 2x 120v legs).

His loads are:
400Amp service at House (divided into 2x 200amp panels) - current fed with a 50Kva 240/120 from POCO.
200Amp service at Guest House (1x 200amp panel - current fed with a 15kva 240/120 from POCO.

he wants to add a
100-125 Amp service at Barn 1 (600 feet from Guest House)
200 Amp service at Storage Bldg (650 Feet from guest house)
50-60Amp service at each of the Gate and Storage Barn (400-600 feet from main House)

I come to the forum because traditionally this is easy - take in 1000A or larger service at primary 3ph and step it down to 120v everywhere - do this every day. But this one is distributed and making me second guess the design.

My design is - so far -:
1) Let POCO upgrade service to 200a@480v (100kva transformer gives me 800 amps of total 120v capacity) at the Main House
2) Install a basic 480V 1ph panelboard at the handoff from Poco with 4 distribution breakers - 50A@480V each: 1-2 facing the House, 3-4 facing North and South feeds to other areas on the property.
3) Install 2 25kva 480/240 x 240/120 single stepdown transformers at the house to feed the 2 existing 200a panels.
4) Run 250MCM/250MCM/4/0 in conduit underground to the South destinations (Guest House, Barn 1, Storage Bldg -the furthest point is 800 feet away from the distribution panel)
5) Tap the 250-250-4 at each location to put 480/240 x 240/120 stepdowns of 15kva (at Guest House), 15Kva (at Barn 1), and 25Kva (at Storage Barn).
6) (future) Run 250-250-4 in conduit underground to the North destinations (Gate/Storage Barn) with 5kva transformers at each little site.

That puts 115 kva of transformers behind a 100kva Primary feed, which I should be fine doing considering this is agricultural and residential application?
Have I missed anything here? Do I need a primary disconnect at the Poco handoff? They will CT meter on the pole so no meter can required.

Thanks! (Not sure if I'm in the right forum, this may be a calculations question - if so, mod please feel free to move.)
jwb
 

kwired

Electron manager
Location
NE Nebraska
Can your POCO give you any demand history? I bet your demand isn't as high as you think it is.

Is easier and usually less cost to have POCO upgrade their service transformer if load increases then to upgrade customer owned transformers, pus they will push their transformers harder then what NEC recognizes is possible.

Seems like money would be well spent to bring POCO service transformer as close to a central location as practical between all the loads. Or at least bring it closer to the largest loads. If owner don't want poles then go underground with the primary.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician Semi-retired
If I saw someone asking for that much power, I would suspect he was into indoor horticulture. The kind you don't want the Feds to see.
 

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
It might be easier with a sketch of locations, distances and calculated loads to strategize solutions.

I helped a workmate a month ago develop a strategy on his little ranch. His involved 1300 feet. Best solution, given what he wanted and his loads, is going to be installing farm panels at the first two locations and then a load center at the last using the same run. No transformers on his end. Parallel run of same size conduit for expansion or changes.
 

kwired

Electron manager
Location
NE Nebraska
Look at costs, if service is already near the house you want to use 2 25kVA transformers for, you are spending 2000-3000 just on the transformers, plus you need 600 volt gear on the supply side. Since the house is near the service, you likely don't increase conductor size for voltage drop.

You then have another 3000-4000 in transformers plus 600 volt gear at the south destinations.

Is running larger conductor or even parallel conductors for the 800 foot run going to cost more or less then the transformers and extras that go with them? Consider actual load when determining what size conductors are necessary, just because a building has a 200 amp main panel doesn't mean it will ever draw 200 amps.

You do have the benefit of smaller grounding conductor with the 480 volt feed and no neutral conductor is necessary with the 480 volt feed.

Trenching is about same cost whether you run 120/240, 480, or 7200 volt lines, what you throw in the hole and what other equipment is needed at each end is the difference in cost.

If the load is there it may be worth while though.
 

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
Look at costs, if service is already near the house you want to use 2 25kVA transformers for, you are spending 2000-3000 just on the transformers, plus you need 600 volt gear on the supply side. Since the house is near the service, you likely don't increase conductor size for voltage drop.

You then have another 3000-4000 in transformers plus 600 volt gear at the south destinations.

Is running larger conductor or even parallel conductors for the 800 foot run going to cost more or less then the transformers and extras that go with them? Consider actual load when determining what size conductors are necessary, just because a building has a 200 amp main panel doesn't mean it will ever draw 200 amps.

You do have the benefit of smaller grounding conductor with the 480 volt feed and no neutral conductor is necessary with the 480 volt feed.

Trenching is about same cost whether you run 120/240, 480, or 7200 volt lines, what you throw in the hole and what other equipment is needed at each end is the difference in cost.

If the load is there it may be worth while though.

Completely agree. Thus the request for a sketch on locations and actual loads (calculated or otherwise).
 
If this is all just residential and residential shop stuff, I would skip the transformers and just stick with 240. 800 feet is no prob at 240 for resi loads. Of course if the guy wants and over sized and over elaborate electrical system and is ok paying for it, knock yourself out.
 
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