100a Barn sub to new barn Sub

[Cb-man]

so last year I ran #2 copper to an existing barn and put up a 100A panel. feed from a disconnect right out of the meter then 200 ft to the barn.
thinking I was going to finish this barn.

Well this year I went and built a new pole barn. I'm trying to figure out the best way to get another 100A service to it.
I no where need 100 amps in the old barn now. only lights and a garage door opener.

the new barn is about a 125ft run from the panel in the old barn. if I run #2 copper from the panel to the new barn voltage drop wise on #2 looks like I will be limited to 70 Amps.

any body have any suggestions on what to do?

the new barn with be more lights and outlets. a 2 post lift. 220v compressor on a 30a breaker and only a 120v welder for now. obviously not all used at once.

easiest to me seems to be throw a breaker in the old barn panel and feed it that way but I am curious as to the wire size that will fit in a 100a breaker

 

[tyme2par4]

I believe most 100A breakers can handle up to 2/0 Wire. They are sized for aluminum wire, and usually at least one size larger to account for longer lengths.

 

[matt_i]

Seems to me like your 70A is enough to run all that you have listed there. Could probably run a gas-fuel heater as well. I know for sure that a 100A will take the #2 Cu wire. Square D has a table somewhere with definitive information that I found by google searching breaker-wire-size or the like.

 

[Cb-man]

thanks man,
I have been using the voltage drop calculator on SouthWire website. with #2 copper I was just worried about the distance. its 200 ft to the first panel then 120 to the new barn. so #2 copper from the meter to the new barn would essentially be a 320 ft run

 

[tyme2par4]

Why not use AL wire? It'll probably save you some serious coin at that distance.

 

[wyliesdiesels]

thanks man,
I have been using the voltage drop calculator on Southwire website. with #2 copper I was just worried about the distance. its 200 ft to the first panel then 120 to the new barn. so #2 copper from the meter to the new barn would essentially be a 320 ft run

I do calcs by hand

Heres my calcs:

70a 320' #2 cu = 8.5v drop / 3.5%

Not 3% which is only a recommendation but not bad. And you probably wont hit 70a.

With #1 cu and 70a= 7.2v drop / 3%

If you want to save some change and use aluminum you will need 2/0 al for a 70a load to stay @ 3%. More on this below.

Dont forget 2 rods, ground bar kit(s) and isolated neutral bars.

Also, need main disconnect if more than 6 breaker handles.

Why not use AL wire? It'll probably save you some serious coin at that distance.

#2 cu will cost about $1100-$1200.

2/0 AL MHF will cost about half that. So yes some serious coin!

EDIT: My brain was thinking OP needed 320' of wire. WHOOPS

500' roll of #2 @ home depot here is $570. Then .49 cents/ft for green #10 or $86 for 500' roll of #10.

So $630 + tx for cu or about $230+ tx for 2/0 AL MHF. Conduit will need to be slightly bigger so expect the AL wire to cost about half as much as the copper.

 

[matt_i]

I'm not sure of that estimate, #2 Cu THH/WN spool of 500' is around $522 @ home dee

http://www.homedepot.com/p/Southwire-500-ft-2-Black-Stranded-THHN-Wire-20502101/202316586

One could easily extract the 120' x 3 = 360' from that, could even run a #2 ground even though its not required in that gauge and stay under the 500' limit (and not have to purchase another wire). IOW the alternative is to purchase another wire like 120' of #6 THH/WN green instead but have left over 140' of #2...not sure that's worth it.

Conduit isn't free but it isn't $500 worth either, in a 120' run...

 

[wyliesdiesels]

I'm not sure of that estimate, #2 Cu THH/WN spool of 500' is around $522 @ home dee

http://www.homedepot.com/p/Southwire-500-ft-2-Black-Stranded-THHN-Wire-20502101/202316586

One could easily extract the 120' x 3 = 360' from that, could even run a #2 ground even though its not required in that gauge and stay under the 500' limit (and not have to purchase another wire). IOW the alternative is to purchase another wire like 120' of #6 THH/WN green instead but have left over 140' of #2...not sure that's worth it.

Conduit isn't free but it isn't $500 worth either, in a 120' run...

yeah whoops.

When i did the estimate I was using 320' for the wire length.

DOH! He only needs 120'.

Will edit....

 

[Cb-man]

Thanks for the help guys.
What size would be needed to get a full 100a at 320ft?

Also what would be the best way to go from the first 100a panel to the next 100a panel?
Just a break in the first panel?
No main load center to split them?

So the first sub panel needs grounds and neutrals isolated. No ground screw then the sub panel to the new garage should have the ground screw in?

What is a neutral bar kit?
The panel already has a lug strip for neutrals

 

[ard]

OP is running 100Amps on #2 copper. Is that permitted?

I have 100A at 330 ft. 2/0 copper. Beast to pull.

 

[wyliesdiesels]

Thanks for the help guys.
What size would be needed to get a full 100a at 320ft?

would need 2/0 cu or 4/0 al

Also what would be the best way to go from the first 100a panel to the next 100a panel?
Just a break in the first panel?
No main load center to split them?

You would put a breaker, that is listed for that particular panel, in the subpanel.

So the first sub panel needs grounds and neutrals isolated. No ground screw then the sub panel to the new garage should have the ground screw in?

What is a neutral bar kit?
The panel already has a lug strip for neutrals

On new installs, all subpanels(all panels after main service panel) need to have an isolated neutral bar/ground screw removed.

And go back and reread what i previously said. I said ground bar kit NOT neutral bar kit.

OP is running 100Amps on #2 copper. Is that permitted?

I have 100A at 330 ft. 2/0 copper. Beast to pull.

yes, why not? #3 cu is rated for 100a... Op is talking about 70a on #2 cu @ 320'....

 

[Cb-man]

I'm not sure if it matters or not but the barn panels are not powered from the main house panel. They are powered straight from the meter through a 100amp breaker at the house

So there is already a place to put the grounds in the panel. What does the ground bar kit do?

 

[OneOfEm]

I'm not sure if it matters or not but the barn panels are not powered from the main house panel. They are powered straight from the meter through a 100amp breaker at the house

So there is already a place to put the grounds in the panel. What does the ground bar kit do?

If your subpanel doesn't have a way to isolate the built-in ground bar from the built-in neutral bar, you'll need to add a separate ground bar. Neutral-ground can't be connected (bonded) in a subpanel in a detached location.

 

[Cb-man]

So for the first barn my electrician told me #2 copper for 100 amp panel.
So if there is #2 to the first panel what if I run 1/0 to the second panel?
Less voltage drop from the sub panel.