700' voltage drop

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  #1  
Old 07-01-15, 07:51 PM
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700' voltage drop

Hi,
I'm adding a mobile home to my property and the location will be approximately 700' from the overhead drop. I just wanted to double check my calculations and make sure I put the right info in the calculator before spending any money. I used the online calculator from southwire and it said I need parraleled 750 kcmil for 100 amp service. Is that right?
Here are the specs

700 foot run in conduit
Single phase 120/220
100 amp service
@ 3% max voltage drop
 
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  #2  
Old 07-01-15, 07:55 PM
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Forgot to say it's aluminum wire
 
  #3  
Old 07-01-15, 08:19 PM
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Welcome to the forums! That's a long run and a bunch of money for aluminum. Is there no way to have the POCO set a pole closer so your run wouldn't take such large wire?
 
  #4  
Old 07-01-15, 08:25 PM
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You do not need paralleled 750 kcmil for 100 amps (6 total wires + ground), you would need one 750 kcmil per conductor (3 total wires + ground).

Now here's the thing you didn't consider: Voltage drop is based on load (current), if there is no load, there is no voltage drop. I suggest doing a load calculation on your mobile home and find what the expected load will be. Then plug those numbers into your voltage drop calculator to find what size wire you will need.

Also, remember that limiting voltage drop is not a code requirement, it is only an informational note. However, based on your distance, I would recommend coming close to the wire size the calculator comes up with.
 
  #5  
Old 07-02-15, 06:00 AM
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The "load calculation" described in the back of the NEC is also used to determine the "size" of the service you will need e.g. 100 amps.

For all intents and purposes, if the wires from the pole transformer to the building service panel will support X amperes for Y% (you selected 3%) voltage drop then your service size is X amps.

An obscure note: If at one moment the amperes draw on one leg of the 120/240 volt service is close to the maximum and the amperes draw on the other leg is somewhat less, then the voltage drop on the more heavily drawn leg will be greater, percentage wise, than what you calculated for "a 240 volt line." So you may want to allow a little more headroom.
 

Last edited by AllanJ; 07-02-15 at 06:26 AM.
  #6  
Old 07-02-15, 06:29 AM
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Thanks for your help!

I will do the load calculation for sure. Thanks that helps a lot! I was like man if its parralleled I can't afford it, it was going to be like $13,000 just for wire!

I am planning on looking into moving the drop, but I am assuming it will require getting the AHJ involved... which I'm hoping to avoid if I can.

One more question

Could I get away without running a ground wire if I ground it at the mobile home via a ground rod? I know I'm supposed to ground the neutral at the first means of disconnect, and will need a disconnect at the meter at the drop, but wire is expensive😜
 
  #7  
Old 07-02-15, 06:38 AM
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Thanks AllanJ! Will do. Load calculations and voltage drop are new for me. I've been a commercial apprentice for four years and still haven't had to do one for a service.
 
  #8  
Old 07-02-15, 06:49 AM
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A separate ground wire is needed downstream from the first master disconnect. So if there is a disconnect at the utility pole then you will need to run a 4'th wire as a ground wire the 700' to the home.

You will also need the pair of ground rods near the service panel in the home.
 
  #9  
Old 07-02-15, 08:04 AM
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You will also need the pair of ground rods near the service panel in the home.
You only need a pair of ground rods if required. (see NEC) In my area we never are required to have two ground rods unless there is not a water service, city or well.
 
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Old 07-02-15, 03:33 PM
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I am assuming it will require getting the AHJ involved... which I'm hoping to avoid if I can.
You're not going to jump over this obstacle. They will be, or should be already involved.
 
  #11  
Old 07-02-15, 06:28 PM
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I would see if they will set additional poles and a transformer closer to the house.
 
  #12  
Old 07-06-15, 07:54 AM
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Is there a particular reason you need 100A at the mobile home?
 
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