100 amp sub panel pole barn

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  #1  
Old 04-10-07, 10:39 PM
R
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Question 100 amp sub panel pole barn

What size wire & type would i need to run 100 amp to pole barn approx. 150ft. from main?Would #6 copper do & what size aluminum would do?Plan to run through conduit 18" underground,also plan to put 100amp main in sub at pole barn.Am i ok by running #8 or #10 for bonding ground back to main panel & do i also need ground stake at pole barn?Whoops!forgot to mention 220 volt please.Again is it ok to put 100amp as main breaker in sub panel & main feed panel?Would appreciate any advice and help on this project!

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Old 04-11-07, 08:00 AM
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Let's ignore voltage drop for a minute. You're not required to consider it anyway, and I don't have enough information to consider it yet.

What size wire you need for a 100-amp feeder depends on which table the inspector requires you to use (they use different tables in different areas), whether you are using wires or cables, and what type of metal. If you use copper, the answer is certainly going to be #2 or #3 or #4, certainly not #6. Aluminum will be 1/0, 1 or 2.

Yes, you'll need a grounding rod. Yes, two 100-amp breakers is okay (and good). #8 copper or #6 aluminum is sufficient for the EGC (Equipment Grounding Conductor) between the buildings. You'll need to use #6 or #4 copper for the GEC to the grounding rod (depending on how you protect it).

To properly consider voltage drop, we need to know what kind of loads are in the barn.
 
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Old 04-11-07, 08:16 AM
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> What size wire & type would i need to run 100 amp to pole barn approx.
> 150ft. from main?

The minimum wire size you can run to a 100A panel is #4 copper or #2 aluminum. If you know that the panel is going to operate close to its 100A rating, then I would go larger than that. If the expect load is less than say 80A, #2 aluminum would be wire of choice. Aluminum is a little tricky to install, but copper would be very expensive for a 150' run. Please post back if you need tips on aluminum wire termination.

> Plan to run through conduit 18" underground

My recommendation is 4 conductor aluminum underground service cable 2/2/4/6 or 2/2/2/6. This is a cable assembly usually sold as 100A mobile home feeder. It can be buried directly in the ground without the need for horizontal conduit. You still need conduit for protection on the ends where the cable runs out of the ground and into the buildings.

> also plan to put 100amp main in sub at pole barn.

A main breaker is required in the barn because it is a detached building.

> #8 or #10 for bonding ground back to main panel

You need #6 aluminum or #8 copper. If you buy the aluminum cable I suggested, the ground is included.

> do i also need ground stake at pole barn?

You need at least one ground rod at the barn. It should be 8' x 5/8" copper clad rod driven flush to the ground. Use an acorn clamp on the top of the rod and run some bare #6 copper from the rod to the ground bar of the barn's panel. This wire must be copper, aluminum is not allowed for ground rods.

This is also a good time to mention that the barn panel needs to have separate ground and neutral bars. This usually requires you to buy a ground bar kit for the panel and to remove a bonding screw or strap from the panel. The instructions for the panel will say how to do this. When you install circuits in the barn, keep the grounds and neutrals on the correct bars.

> Again is it ok to put 100amp as main breaker in sub panel & main
> feed panel?

Yes.
 
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Old 04-11-07, 10:47 AM
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Thumbs up 100 amp garage sub panel

Great help guys-Ben & John.Yes could use some help & advice on aluminum wire termination.Will probably opt for 2/2/4/6 or 2/2/2/6 aluminum for supply run.Thanks Ben,100 amp. mobile home feeder great idea.Will still probably place in conduit since part of run may come under some light traffic.Is it ok to run partial with coduit?
 
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Old 04-11-07, 11:38 AM
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> could use some help & advice on aluminum wire termination

After you strip the wire, shine up the individual strands with a wire brush or emory paper. Apply lots of non-oxidation grease (NOALOX) to the bare aluminum; I use a plumbing flux brush to work it down between the strands. You can get a tube of it in the electrical aisle for a few dollars. Finally, when you terminate the wire on the screw lugs, make sure to get the torque to the correct in-lbs using a torque wrench. The panel label and instructions will tell you the correct value for that brand.

> Will still probably place in conduit since part of run may come under
> some light traffic. Is it ok to run partial with coduit?

You could use a schedule 80 PVC conduit sleeve if you wanted for part of the run. I would probably just bury that section deeper instead of using conduit. Minimum depth allowed on residential land is 18" to the top of the cable, but if you've got a trenching machine it's no big deal to go 24" or 30". Be careful to keep rocks out of the backfill; if you've got rocky soil, the first couple inches of sand or peastone backfill is a good idea.
 
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