Sub Panel Question

[98CarmineRedTN]

Hello,

I have a question that seems to be asked over and over, but I would like a consensus.

I have a pole barn that is approximately 300 ft from my main panel (we haven't dug the trench yet).

I would like to install a 100AMP sub panel with a 100 AMP from my main panel.

1 - What wire size do I need in either copper or aluminum?
2 - Will there be a voltage drop to consider ( I am thinking Yes)
3 - I will be using conduit, but what type of calbe do I need to use, (SER, USE, etc.)

I live in Tennessee if that matters from a code standpoint.

Thanks to the gurus, and I appreciate the help.

 

[pattenp]

Aluminum is the best way to go because of cost. If you can get Mobile Home Feeder (MHF) that's what I suggest. I think 4/0-4/0-4/0-2 is what you'll need to use for that distance, besides the MHF comes in 2/0 then 4/0. You may be okay with the 2/0 if your loads don't exceed around 80A. You can use USE only wire but it needs to terminate on the outside and then transition to SER for the inside. The MHF can be run inside in conduit.

Edit: The problem you'll have with the 4/0 is getting it connected to a 100A breaker because it won't fit. You can splice on a short piece of 2/0 to the 4/0 to fit the breaker. The more I think about it, 2/0 would probably be fine for the whole run. I assume you won't be maxing out the 100A service. The 2/0 MHF size will be 2/0-2/0-2/0-1

 

[astroracer]

What is the cost to have a meter installed on the barn? May be cheaper then a 1,000 ft of 4/0 cable...

 

[98CarmineRedTN]

Aluminum is the best way to go because of cost. If you can get Mobile Home Feeder (MHF) that's what I suggest. I think 4/0-4/0-4/0-2 is what you'll need to use for that distance, besides the MHF comes in 2/0 then 4/0. You may be okay with the 2/0 if your loads don't exceed around 80A. You can use USE only wire but it needs to terminate on the outside and then transition to SER for the inside. The MHF can be run inside in conduit.

Edit: The problem you'll have with the 4/0 is getting it connected to a 100A breaker because it won't fit. You can splice on a short piece of 2/0 to the 4/0 to fit the breaker. The more I think about it, 2/0 would probably be fine for the whole run. I assume you won't be maxing out the 100A service. The 2/0 MHF size will be 2/0-2/0-2/0-1

Thanks for your reply. I guess, I am reading NEC 310.16 wrong. I thought 1/0 would be sufficient in AL. Isn't 1/0 AL rated for 120 amps at 75C for USE type cable...

Thanks for the help...

What is the cost to have a meter installed on the barn? May be cheaper then a 1,000 ft of 4/0 cable...

I wish I could, but the cost of another meter is prohibitively expensive.

 

[Stuart in MN]

Thanks for your reply. I guess, I am reading NEC 310.16 wrong. I thought 1/0 would be sufficient in AL. Isn't 1/0 AL rated for 120 amps at 75C for USE type cable...

1/0 would be okay probably out to 200 feet or so, but since the pole barn is 300 feet from the house the wire has to be upsized to keep the voltage drop within acceptable limits.

 

[pattenp]

You're not reading the table wrong. I was accounting for voltage drop because of the 300ft distance. #2/0 AL with a 80 amp load will have a VD of 3.2%. The NEC suggests no more than 3%. I was using 80% load on the 100A service as an example. The 1/0AL with an 80A load reaches the VD of 3% at 225ft. So with the 100A service you can use 1/0, but once your load passes 60-65 amps then you'll realize voltage drop in excess of 3%. With the 1/0 at 80A @300ft you be at 4% VD. That's really not that bad.

Thanks for your reply. I guess, I am reading NEC 310.16 wrong. I thought 1/0 would be sufficient in AL. Isn't 1/0 AL rated for 120 amps at 75C for USE type cable...

Thanks for the help...



I wish I could, but the cost of another meter is prohibitively expensive.

 

[98CarmineRedTN]

1/0 would be okay probably out to 200 feet or so, but since the pole barn is 300 feet from the house the wire has to be upsized to keep the voltage drop within acceptable limits.

You're not reading the table wrong. I was accounting for voltage drop because of the 300ft distance. #2/0 AL with a 80 amp load will have a VD of 3.2%. The NEC suggests no more than 3%. I was using 80% load on the 100A service as an example. The 1/0AL with an 80A load reaches the VD of 3% at 225ft. So with the 100A service you can use 1/0, but once your load passes 60-65 amps then you'll realize voltage drop in excess of 3%. With the 1/0 at 80A @300ft you be at 4% VD. That's really not that bad.

Thanks Guys. I appreciate the help. I will post back once we have an actual trench to measure, it will be far more accurate.

 

[rockwithjason]

Edit: The problem you'll have with the 4/0 is getting it connected to a 100A breaker because it won't fit. You can splice on a short piece of 2/0 to the 4/0 to fit the breaker. The more I think about it, 2/0 would probably be fine for the whole run. I assume you won't be maxing out the 100A service. The 2/0 MHF size will be 2/0-2/0-2/0

you can use pin connectors for this

 

[pattenp]

You can use pins but the pins for 4/0 are large and I believe they will touch together when trying to insert them in the breaker. That's just my thought. I have not tried to put 4/0 reducer pins in a 100A breaker.

Edit: I didn't think about it, but there are offset reducer pins. The only other thing is you need a crimping tool to put the pins on.

Edit: The problem you'll have with the 4/0 is getting it connected to a 100A breaker because it won't fit. You can splice on a short piece of 2/0 to the 4/0 to fit the breaker. The more I think about it, 2/0 would probably be fine for the whole run. I assume you won't be maxing out the 100A service. The 2/0 MHF size will be 2/0-2/0-2/0

you can use pin connectors for this

 

[98CarmineRedTN]

Gentlemen,

First off I must apologize for being gone for 8 months, but extremely long story short, I am back and ready to wire my pole barn.

The Subpanel is exactly 284 Feet from my main.

Would 2-2-2-6 Copper Wire Work for my application? The reason I ask is I can get this for a song right now.

 

[Speedy Petey]

The Subpanel is exactly 284 Feet from my main.

Would 2-2-2-6 Copper Wire Work for my application? The reason I ask is I can get this for a song right now.

It'll certainly work, but you will NOT get 100A out of it. At that kind of distance, you'll be limited to about 40A

 

[pattenp]

Using #2 CU @ 290 ft with a 65A load will have right at 3% VD. At 80A load the VD will be about 3.7%. I think the #2 Cu is doable but not ideal. If the price is really really good and you don't see having continuous loads pushing to 80A then go for the #2.

 

[98CarmineRedTN]

Using #2 CU @ 290 ft with a 65A load will have right at 3% VD. At 80A load the VD will be about 3.7%. I think the #2 Cu is doable but not ideal. If the price is really really good and you don't see having continuous loads pushing to 80A then go for the #2.

Thanks for the feedback... That was what I calculated, but wanted a 2nd opinion...

 

[Speedy Petey]

Sorry guys.
98, even though you wrote copper I still had AL in my mind as we do not use CU URD or SE cable here. Patten's numbers are correct, not mine.

 

[98CarmineRedTN]

Sorry guys.
98, even though you wrote copper I still had AL in my mind as we do not use CU URD or SE cable here. Patten's numbers are correct, not mine.

No worries at all. I wouldn't be considering copper, except for the great deal I am getting...

 

[BMS]

You must be getting a really great deal. I priced copper and aluminum for my subpanel (80' run) and it was $1.85/ft for aluminum versus $6.35 for copper. Aluminum was a no brainer.