Help! residential voltage drop calc+gear problem

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cceinak

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Owner is building a very nice house with wonderful view of mountains. Does not want utility to bring highvoltage line into property, impact of view. He wants to set up meter loop on pole for service drop then go underground to a outside, nema 3R panel w/200 amp main breaker. Panel will feed outside branch ckts, and also 200 amp main panel in house. This 200 amp panel in house would be fed by 2 pole 200 in outside panel. Distance from service drop to outside panel is 700 feet. When i do the voltage calcs for 200 amp, 240 volt, 3% on feeder comes up to 500 MCM's. What is the best way to work with 500's in gear that is not at all user friendly with this big of wire. A 200 amp main breaker is not even rated for 500's. I was thinking about bringing the 500's into a nema 3R junction box next to the outside panel and tapping down to 2/0. Also, what about the 200 amp meter loop, same idea? Also, i was thinking about running a three wire from the meter loop to the outsidepanel. All direct bury, no metal conduit. Drive a ground rod and bond the nuetral to the ground. Call it my new service. Sooo, am i all wet on the volt calcs, ideology, intent? Just the expense of 2100 feet of 500's is over $6000.00 I have not done a nuetral calc to see if i could drop the nuetral size yet. I am still in the planning stage, and with the cost of all of this, i want to get as many options as possible. This is a lot of money for the owner, so I want to give hime the best possible job I can!
thanks everyone, this site is great!
 
Re: Help! residential voltage drop calc+gear problem

I come up with 600 kcmil per phase for a load of 200 amps at 240 volts 700 feet of run resulting in 3% VD.

If I figure the run at 160 amps it needs 500 kcmil.

My suggestion is this is the time for an engineer.

It may be cheaper to have a pad mount transformer at the residence.

Edit sorry I did the calcs for aluminum, I fixed it now.

[ November 20, 2003, 07:20 PM: Message edited by: iwire ]
 
Re: Help! residential voltage drop calc+gear problem

are you sure iwire?? i just checked it out on a few internet voltage drop calculators, they come up with the same thing. 500's, what am i missing??
thanks
 
Re: Help! residential voltage drop calc+gear problem

Your not missing anything I have edited my post, I had my VD calculator set for aluminum wire.

I come up with 600 kcmil now for 200 amps or 500 kcmil for 160 amps, a reasonable figure I think for a 200 amp service.
 
Re: Help! residential voltage drop calc+gear problem

phewww, good news, wondered what the heck i did! Even though 3 500's are better than 6, it still looks like a pain in the neck!
 
Re: Help! residential voltage drop calc+gear problem

Code wise I might be off base here, but is it possible to transform your voltage up to 480 after the service disconnect at the property line, and then drop back to 240 with a second xfmr at the house?. Smaller wire but 2 xfmr's and also overcurrent devices to add to the soup.
 
Re: Help! residential voltage drop calc+gear problem

Even with my first mistake taken care of I still suggest getting an engineer on board with this.

The costs are going to be high enough to justify this.

There are so many ways to accomplish this task and none of them are cheap.

I would not want to roll the dice on this much money.

My suggestion of a pad mount transformer was to have the high voltage utility feed buried all the way up to the house and have a small transformer at the house.

It would only need to be about 3' square, the same ones you see in a neighborhood with underground services.

With the costs involved of the copper and the problems of terminating the 500s to the 200 amp gear it could be less money to go this route.

You would definitely need junction boxes on both ends as even if you can change the lugs on the equipment you will not have the required and needed wire bending space.

I agree the 3 wire feeder with bonding at the house is the way to go. 250.32(B)(2)

If you do run a grounding conductor it will need to be sized up in relation to the ungrounded conductors. 250.122(B)
 
Re: Help! residential voltage drop calc+gear problem

Iwire's method (pad mounted, high voltage transformer) is the way to go. The utility will do that part of the installation for a fee (around here anyway, if you dig the trench). Your savings on wire, equipment and labor will offset most if not all of that cost. The best thing about this installation is the 700 ft. feed and transformer will belong to the utility thus eliminating any future maintainence problems/costs to the owner.
steve
 
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