new service to barn/ voltage loss calculation

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Old 09-28-00, 01:49 PM
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I am preparing to set up a new service to my barn. I will be running a separate meter for this insatllation. I plan to run the service cable from the meter to the main breaker under ground. This distance is approximately 400 to 500 feet depending on the path of travel. What size wire do I need for a 100 amp service. I plan to run only lighting and receptacles for small appliances (hand tools, etc.) What size breakers would be best 15 amp? 20 amp?
 
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Old 09-28-00, 03:48 PM
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hello PSFarm9550,
the forluma for wire size takeing into account the voltage drop is as follows
(2 x K x D x I) / VD
K = 12.9 for copper, 21.2 for alum
D = distance 1 way
I = amps of load
VD = voltage drop permited (supply voltage x X%) 2% feeders; 3% branch circuits; 5% total

i would recomend u run 20 amp circuits for the outlets, this requires a min of #12 wire. i would put no more then 8 outlets on a circuit.
as for the lighting u can run eather 20 amp or 15 amp circuits 15 amp requires a min of #14 wire

 
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Old 09-28-00, 04:25 PM
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Sparky, Thanks for your rapid response. You have been a big help. Now if I can do the math I should be OK. If I have any more questions I will let you know. This forum is new to me but it is GREAT.
 
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Old 09-28-00, 09:11 PM
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The following are the voltage drops calculated for a 500' run in either aluminum or copper feeders and with the stated amp loads, using 240 volt power source and on feeders to detached structure.

30 amps
#2 Al. = 3.32%
#4 Cu. = 3.85%
50 amps
2/0 Al. = 3.53%
#1 cu. = 3.21%
100 amps
250kcml Al. = 3.53%
3/0 Cu. = 3.19%

Rememeber that the Fpn Note in the NEC says that 5% on a feeder or 5% on a branch or 5% on a combination of a feeder and a branch end of line is considered acceptable. The above calculations keep you below 4% this should give you an approximate 1% voltage drop left for the branch circuits in the structure.

Hope this helps

Wg
 
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Old 10-12-00, 12:13 PM
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This is for WGoodrich.
Thanks for your calculations on the voltage drop for a 500 foot run from the meter to the main. After discussing the plans with the electric Company and the local inspector, the run will only be 350 feet (underground)from the meter to the main breaker. The electric company will run the service line from the transformer to the meter which is approximately 100 feet. (overhead) Will this change the calculations for wire size. I am using a 100 amp service but will only have up to five circuits for lights and outlets with three to five on each 20 amp circuit. I do not mind a little overkill but I don't want to buy a sledgehammer to drive a tack.
Any way thanks for your input you have been a big help.

PSFarm9550
 
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Old 10-14-00, 07:50 AM
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The way that I understand is that the power company is running 100' and you are running 350'. If this is the situation the distance calculated for voltage drop would essentially be around 50' less than originally calculated. This is because the voltage drop is calculated from the transformer causing you to add the 100' onto the 350'totaling 450' The difference would be minor. I would not change the design in the feeders as originally calculated because you variables during the life of the barn would change as much or more than the 10% or so in adjustment in the voltage drop calc.

Hope this helps

Wg
 
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Old 10-16-00, 08:15 AM
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Wink

Thanks for your help.
 
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Old 11-21-01, 02:35 PM
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Poor tape job

We want to paint a couple of rooms, but the original drywall tape has lifted along the ceiling. What is the best way to re-attach this so that I can paint over it??
 
 

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