What size and how many wires to pull to barn underground?


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Old 10-10-14, 02:09 PM
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What size and how many wires to pull to barn underground?

Hi

I pulled wire to the barn several years ago, but it seems either the gophers ate through it or the sandy ground destroyed the wire. In any case, here are the particulars:
- distance from the Main circuit breaker - 170'

- Running off power in barn
- 10 - 100 watt bulbs
- Stock tank heater (1500 watts)
- separate 30 amp outlet to plug in RV

Currently this is being supplied by 2 x 20 amp circuits (RV only plugged in to 20 amp outlet - only when tank heater not in use)

I have learned... I'll be trenching in conduit (PVC)
Looking for inf regarding... if you had to do it again... since I am.
- what size conduit would you bury?
- what size wires would you put in?
- How many wires? cause NO ONE ever adds to what is ONLY going to be ran off the power - right?.
- given the length, should I run 240v instead of 120v?

Note this is a working barn (horses, cows, chickens, pigs occassionally - I won't be hooking up a welder, there are pens in the barn, not the office type of pens either :-)

This is in central MN - do I need to bury this below the frost line? - the prior wire was put in about 5' deep, but then I hit the water table, and had to raise it up to about 18" below the surface.

Thanks

Please let me know if more info is needed.
 
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Old 10-10-14, 02:34 PM
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Put in a 60A sub panel.

Based on the CEC... NEC may vary...
You will need a 2 pole 60A breaker for your main panel.
Pull in #4 AWG RWU90.
4 wires: hot, hot, neutral, and a #6 AWG bond.
Your sub panel will give you 120V and 240V.
1 1/4'' PVC buried 3' deep. But I would use 2 1/2'' or even 3'' PVC in case you ever decide to upgrade to a 100A panel. Then you would only need to pull wire and not dig anything up again.
 
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Old 10-10-14, 06:11 PM
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I pulled wire to the barn several years ago, but it seems either the gophers ate through it or the sandy ground destroyed the wire. In any case, here are the particulars:
It may be fine, how did you determine it was bad and needed to be replaced? Sandy soil is ideal for direct burial cable, it's rocks that move and cut into it. Is your soil rocky? Was it 3 wires or 4 wires? What size and type wire was it?

For a new feed in conduit, I wouldn't put anything smaller than 2" PVC conduit in the ground for that length.
 
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Old 10-11-14, 11:37 AM
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I also live in central MN and our location is also very sandy. You must be north of the Mississippi.

You do not need to bury the feeder below the frost line. If you use direct burial cable you need to bury it 24". If you use conduit, which I recommend, you need to bury it 18".

I also think a 60 amp feeder will work for you, so #6 THHN/THWN or #4 Aluminum XHHW will suffice in PVC conduit. IMO 1 1/2" is plenty big.
 
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Old 10-11-14, 12:03 PM
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Tolyn,

Does the NEC allow T90 for outdoor use? Here we have to use RW, and running underground is RWU.
And I say #4 AWG copper to compensate for the length of the run. Should he ever come close to fully loading that panel he should still have about 115V.
 
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Old 10-11-14, 01:22 PM
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The general term outdoors could mean a damp area or it could mean a wet area. We generally use wire types outside that contain a "W" such as TW, THW, THWN, RHW, XHHW, etc. I don't know what T90 is, is that a Canadian wire type?
 
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Old 10-11-14, 01:42 PM
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Mr Awesome, you need to translate your cable/wire ID's

THHN (I think your T90) is almost always double rated as THWN and is approved for outside. Direct burial will mostly be URD, but I think there is some XHHW that is approved for direct burial.

IMO there is not much concern for voltage drop. Remember that voltage drop is effected by load, if there is not load, there is no voltage drop. His loads sounds fairly small to me, and the RV plug in will be a non-coincidental load with the tank heaters.
 
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Old 10-11-14, 04:06 PM
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Yes sorry, T90 = THHN. I wonder why the difference (CEC vs. NEC), THHN is not under any tables for being allowed outside or underground.
And Based on his known load I agree with you, but my assumption is maybe the panel gets fully loaded one day. Personally I would up the wire size and avoid possible future problems.
 
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Old 10-11-14, 04:20 PM
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THHN is not rated for wet conditions south of the border either but they don't really sell THHN here usually. What they sell is dual rated THHN/THWN. Basically best guess to save money on inventory they just mark THWN as usable for THHN.
 
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Old 10-11-14, 04:26 PM
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Ahh ok thanks for the clarification Ray.
 
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Old 10-11-14, 10:47 PM
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If this were my project I'd pull 2/4 URD cable. Fused at 60A gives you plenty of wiggle room with little or no voltage drop.
 
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Old 10-12-14, 06:15 AM
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There are some river rock in it the soil. A 4 wire #10 cable was pulled (I can't recall what type it was though) I determine there was an issue with a voltage tester off the breaker there is power, at the far end there is no power.
 

Last edited by dziebol; 10-12-14 at 06:36 AM.
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Old 10-12-14, 05:37 PM
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i'm looking at putting in 2-2-2-4 3e all ser1 (4 aluminum strand cables bundled in a casing). In 1.5 schedule 80 PVC conduit. Would this be appropriate? Will it matter that the this will run through part of a winter pasture, an area where the horses don't get to and than through are area by the barn where the horses can walk? The frost will go deeper where the horses move over the conduit.
At $1.49/foot are there cheaper options (is this overkill?)
 
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Old 10-12-14, 06:01 PM
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SER cannot be used underground.
 
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Old 10-12-14, 07:55 PM
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i'm looking at putting in 2-2-2-4 3e all ser1 (4 aluminum strand cables bundled in a casing).
I'd use separate aluminum Type XHHW conductors that are available at any supply house.
 
 

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