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Old 12-22-2008, 12:07 PM   #1
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wiring new barn questions


Hello Sparkys, I am building a pole barn, inspection required. Here are my wiring plans: One 20 amp circuit from house to barn (about 260' away), 12/2 NW-B w/ grd romex inside barn-disconnect outside barn to first receptacle GFI- to 3 switch box- one for feed room wall mount light, one to floodlight, one to 6 ceiling mount lights plus loft light . All fixtures single bulb keyless (except floodlight). How does this sound in relation to NEC? Can I use this many keyless fixtures, and what size wire would I need to run underground (18" deep in conduit) from house, about 260' away. When electrician wired my house he said attic light had to have receptacle, does this apply to loft light and/or ceiling lights? Thanks in advance for replies.

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Old 12-22-2008, 07:07 PM   #2
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At 260' you will need a #4 copper or #2 aluminum to get your 20 amps to the barn. Use type NMC or UF inside the barn. You can use a standard switch for the disconnect inside the barn.

No receptacle is required on your loft lights or ceiling lights in the barn. Assuming a 100 watt bulb in each fixture you are looking at using only 800 watts out of the 2400 available on the 20 amp circuit. So your 8 fixtures will be fine.

If the lamps are subjected to damage they must be protected with suitable guards.

I would contact your local inspector to ask about any other requirements or local codes.

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Old 12-23-2008, 12:09 PM   #3
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Good to see you back John. Good advice as usual.
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Old 12-23-2008, 12:19 PM   #4
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Thanks jr. I have talked to two electricians and they said I could use #8 copper wire. I am certainly not saying you are wrong and I appreciate all the time that pros spend on here helping out diy'ers like myself, but are you or anyone else sure about #4 or is #8 ok. Also, if I bury direct, no conduit, i need to go 2' deep, correct?

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Old 12-23-2008, 01:11 PM   #5
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bulldog,
Mr. Clen is giving you code compliant advice. Sure you can run #8. And then you have a huge voltage drop depending on the load applied at the barn. Mr. Clen calculated your voltage drop. Do you want to run smaller wire only to find out your power tools ect will not operate and trip your breaker? Take his advice and do it right the first time. I would not want to have to dig another trench that distance, do you?
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Old 12-23-2008, 01:25 PM   #6
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Quote:
Originally Posted by J. V. View Post
bulldog,
Mr. Clen is giving you code compliant advice. Sure you can run #8. And then you have a huge voltage drop depending on the load applied at the barn. Mr. Clen calculated your voltage drop. Do you want to run smaller wire only to find out your power tools ect will not operate and trip your breaker? Take his advice and do it right the first time. I would not want to have to dig another trench that distance, do you?
The NEC has a requirement for sizing conductors to compensate for voltage drop?
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Old 12-23-2008, 01:46 PM   #7
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The NEC has a requirement for sizing conductors to compensate for voltage drop?
Don't split hairs. Better wording would be to say that the advice was in accordance with best practices.
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Old 12-23-2008, 02:03 PM   #8
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Just keeping everyone honest. Since we're on the topic, would you lose any sleep over a VD that was 6-8% in this case?
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Old 12-23-2008, 02:27 PM   #9
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Just keeping everyone honest. Since we're on the topic, would you lose any sleep over a VD that was 6-8% in this case?
No, not really. 8% makes it about 110 V. The old timers really could say he had "one-ten" at his barn
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Old 12-23-2008, 02:31 PM   #10
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I just want to get enough electricity to power nine 100w lights and pass inspection. I have run drop cords from a 20 amp circuit in garage to build the whole barn so far. btw...I am not one for taking short cuts when building, I used 6" x 6" posts, LVL beams, and poured concrete floor so far (will post pics when done).

I plan on calling inspector about wire size this afternoon to make sure as another source has told me 10 awg is fine. And let me say thanks once again to everyone on this site who takes the time to help each other. I have used this site for advice many times when building house, detached garage and now barn.

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Old 12-23-2008, 09:20 PM   #11
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The NEC has a requirement for sizing conductors to compensate for voltage drop?
The voltage drop references in the NEC are fine print notes and thus not enforceable. But in my humble opinion, voltage drop would be ignored only by a hack, not by a real electrician.

Running a #12 copper to the barn on the 20 amp breaker will satisfy the code.

I gave the best advice I could to the OP. He is free to do what he wishes.
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Old 12-24-2008, 12:40 AM   #12
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Here are some voltage figures for your run. The following is what you'll end up with if you start with 120 volts;

#12 at 10 amps = 110, 20 amps = 100.

#10 at 10 amps = 114, 20 amps = 108.

#8 at 10 amps = 116, 20 amps = 112.

#6 at 10 amps = 117, 20 amps = 115.

#4 at 10 amps = 118, 20 amps = 117.

This is for a constant load, it does not account for the starting current of a motor.

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Old 12-24-2008, 12:16 PM   #13
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Quote:
I just want to get enough electricity to power nine 100w lights and pass inspection. I have run drop cords from a 20 amp circuit in garage to build the whole barn so far. btw...I am not one for taking short cuts when building, I used 6" x 6" posts, LVL beams, and poured concrete floor so far (will post pics when done).
My opinion based on what the above states and a reasonable calculated load. Run a 10/3G multiwire to a double pole switch in the barn. Put a 20 amp doublepole breaker in the house panel to protect this multiwire. Land on a double pole switch to meet the required disconnect. Split the multiwire at this disconnect. Then two runs of 12/2G out of the disconnect box to single pole switches 4 lights on one switch 5 on the other or add a light for 5 lights on each switch. If you turn all ten lights on you will have balanced loads per leg and a considerable advantage in the voltage drop. Essentially reducing the caluclated distance to 260 feet, not 520 feet. Voltage drop is a to the load and back calculation. If you only turn 5 lights on from one switch this will only be around 4 amps on one leg of the multiwire and would be calculated at 120 volts 260 feet one way (520 round trip). Not a problem even on 12 awg. You can add runs of 12 awg to a few receptacles either from the switch boxes or the disconnect box.

The circuit will be similar to this (below) you will have two switches after the disconnect on each leg. The multiwire shares the neutral at the Disconnect.If you run two receptacles and put one on each leg this will help in keeping the load balanced if you are operating two things at once. The receptacles and lights must be wired in on the load side of the disconnect. I wouldn't think you would have any problems with this design for most things you would operate at the pole barn hand power tools and lights etc.. I've shown 10/3 g UF-B but thwn in conduit would be better.

You could also run a 12/3G from the disconnect to a double gang switch box and split it there.
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Old 12-24-2008, 04:00 PM   #14
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Are you sure you will never need more than a 20 amp service in the future? It will be cheaper now to run heavier wire then to do it down the road!

Gary

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