500 foot run

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highendtron

highendtron

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I am supposed to put in an underground run 500 foot from a house to a barn. I plan on using 1/0, 1/0, 2, 2. in 2" pvc. I calculated the voltage drop of 8.7 volts ((2(21.2)(500*100))/105600.The cost of the wire is right at $1000. I would love to drop one more size but think I am at the limit now. Other than walking away or setting a new transformer ( power company wants $3000) I don't see another way...any constructive thoughts?
 
highendtron said:
I don't see another way...any constructive thoughts?
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A pair of your own transformers. Step up to 600v or so at the house, and back down at the barn. The current ratio will be the inverse of the voltage ratio.

You didn't mention the desired feeder ampacity and/or expected load. (The 100 in your equation, mayhaps?)
 
LarryFine said:
A pair of your own transformers. Step up to 600v or so at the house, and back down at the barn. The current ratio will be the inverse of the voltage ratio.

You didn't mention the desired feeder ampacity and/or expected load. (The 100 in your equation, mayhaps?)
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I havent worked with transformers, How would you size them properly if you were wanting 100 amps to go 500 feet and supply 120/240V?

~Matt
 
highendtron said:
...voltage drop of 8.7 volts ((2(21.2)(500*100))/105600.
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First problem: (2*21.2*500*100) / 105600 = 20 volts, not 8.7.

Second problem: I don't know if 20 V is OK or not without knowing the circuit voltage. I am assuming it is 240 V, which means you would have 8.36% drop. If you're OK with 10% or less then you're OK. If you want 5% or less you're going to have to upsize.

I agree with Larry. A couple of transformers would solve your problem.
 
TOOL_5150 said:
I havent worked with transformers, How would you size them properly if you were wanting 100 amps to go 500 feet and supply 120/240V?

~Matt
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You would start with a 240/600 V xfmr at the front end. That is a 0.4 ratio, so the current on your 500 ft run is now reduced to 40 A thus decreasing your voltage drop a good bit. Now you can get by with #4 AWG and still have the same voltage drop as before (if you were OK with it to begin with). Another 240/600 V xfmr at the end will bring the voltage back to where you want it, and this time the ratio is 2.5 because you are stepping down. The 40 A you had on the run is increased back to 100 A.
 
I"m wondering why, if you installing 500' of underground raceway, that you think that $1000 is a lot of money for wire?
 
The transformers are a good idea because it allows you to adjust the tap changers on them and adjust the end voltage to what you want, if the load is relatively constant.
The transformers are a bad idea, because the owner will always be paying for the losses associated with the step up and down. It is also hard to believe that the installed cost of transformers will be less than wire only.
To be within 3% voltage drop for a 240V, 100A load, I get 4/0AWG cu
 
There is so much to consider here.

Should you base the voltage drop calculations on the size of the over current device or should you use the calculated load, or maybe some other figure entirely?
 
ron said:
To be within 3% voltage drop for a 240V, 100A load, I get 4/0AWG cu
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I got the same thing earlier, but I was afraid of bursting his bubble since he was at #1/0 AWG and wanting to go down. :smile:

iwire said:
Should you base the voltage drop calculations on the size of the over current device or should you use the calculated load, or maybe some other figure entirely?
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This is a very good point for the OP to consider. Just because you are installing a 100 A panel with 100 A rated wire doesn't mean that 100 A is necessarily the current you should insert into your voltage drop calculation. If you can calculate the load you expect to have at the barn you can use that number instead of the full rating of the panel/wire. For example, if you knew there would only be 50 A of load, your voltage drop becomes half of what it was when you used 100 A in the equation.
 
Well, I may have to step away from this because of the associated costs relative to what the owner can or wants to afford. The owner expects to run a heater and air conditioner in the respective seasons. He also will be using the barn as a small shop, ie; small tools. His current usage on his house is only averaging 60 amps (14400va)/month. I don't think he will use the barn as a full blown work shop but who knows! He runs a siding business out of his house. He had other bids based on the wire size for a 100 amp service 2,2,2,1. He was expecting $500 for a wire charge. I increased the wire size for the voltage drop , but still feel like $1000 for 1/0,1/0, 2,2. is too much money if the end result will be a 22 volt lose and the customer may be unhappy if he doesn't get the correct voltages at his new barn! I doubled the expected wire charge because I knew that the other bids would be too undersized unless the wire size was stepped up.
 
highendtron said:
Well, I may have to step away from this because of the associated costs relative to what the owner can or wants to afford. The owner expects to run a heater and air conditioner in the respective seasons. He also will be using the barn as a small shop, ie; small tools. His current usage on his house is only averaging 60 amps (14400va)/month. I don't think he will use the barn as a full blown work shop but who knows! He runs a siding business out of his house. He had other bids based on the wire size for a 100 amp service 2,2,2,1. He was expecting $500 for a wire charge. I increased the wire size for the voltage drop , but still feel like $1000 for 1/0,1/0, 2,2. is too much money if the end result will be a 22 volt lose and the customer may be unhappy if he doesn't get the correct voltages at his new barn! I doubled the expected wire charge because I knew that the other bids would be too undersized unless the wire size was stepped up.
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Let the other guy take the job and install #2 conductors.
You can call the customer after the job is finished to sell and install the transformers that he will need to get the voltage up to snuff.:smile:

That and a little "well I told you so" will feel real nice.

steve
 
This is a hard one to explain to owner. Run calcs at 5 % VD and 3%.
$1000 is reasonible for wire with todays costs
 
Ordinarily I wouldn't use one of these in this application but we're talking about a barn here.

How about a buck/boost transformer?

Square D 2S46F would give him 6.6% boost.
Square D 3S43F would give him 10% boost.

Each would be good for the 100 amps @ 240v.

I've installed hundreds of these on tanning equipment and never replaced one. They're also very economical. Just don't wire them wrong or up in smoke they go.
 
Cold Fusion said:
Hummmm...... Are you sure? There seems to be lots on this forum that think the NEC changes the laws of physics :confused::rolleyes::D

cf
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The NEC doesn't change the laws of physics, it defines the laws of physics. If they added a line that said gravity doesn't work from 0700-0730 every Tuesday morning, it would be true by definition. When gravity didn't cooperate, it would need cited for violating the code.

:D:wink:
 
HotConductor said:
Ordinarily I wouldn't use one of these in this application but we're talking about a barn here.

How about a buck/boost transformer?

Square D 2S46F would give him 6.6% boost.
Square D 3S43F would give him 10% boost.

Each would be good for the 100 amps @ 240v.

I've installed hundreds of these on tanning equipment and never replaced one. They're also very economical. Just don't wire them wrong or up in smoke they go.
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Buck boosts will not adjust for changing loads so when they turn on one lamp in the barn the voltage will be to high, once they load up the voltage will be low.
 
iwire said:
Buck boosts will not adjust for changing loads so when they turn on one lamp in the barn the voltage will be to high, once they load up the voltage will be low.
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One lamp???

The reason we use them on tanning booths is increase the voltage so the 24v contactor holds in. If there was a voltage drop as you speak the contactor coil would not hold. I'm talking about tanning beds with FLA of 80a, 240v.
 
HotConductor said:
One lamp???

The reason we use them on tanning booths is increase the voltage so the 24v conductor holds in. If there was a voltage drop as you speak the contactor coil would not hold. I'm talking about tanning beds with FLA of 80a, 240v.
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Apples and oranges. :smile:

You use the buck boost to raise the voltage to the tanning bed because the supply voltage system is to low. You are not using it to compensate for voltage drop.

If you try to use a buck boost to compensate for voltage drop and the load is not constant the voltage will bounce up and down with the load applied.
 
iwire said:
If you try to use a buck boost to compensate for voltage drop and the load is not constant the voltage will bounce up and down with the load applied.
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Of course, the same thing happens with voltage drop without a B/B, too, if the line has that much impedance.
 
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