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Old 06-16-2010, 07:05 PM   #1
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Sizing and best way to run wire for sub panel


Hi,

I'm planning on putting a 100amp sub panel in my barn. I measured out the length and it is about 280 feet of wire. Approximately 210 feet will be underground and about 60 feet will be inside the house. What size wire would I need to run this?

I would like to use direct burial aluminum to keep the price down, but how do I connect that to the copper that I have to run inside the house, some type of junction/disconnect box just outside? And for the barn side, can I run that wire directly to the box?

Thanks,
Chuck

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Old 06-16-2010, 07:41 PM   #2
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Sizing and best way to run wire for sub panel


According to chart for 280' Alum @100a you need 2/0 wires in conduit to keep it ~3% voltage drop

Not sure on size if you use the direct burial cable...?

Hopefully someone else can chime in as I do not use Alum

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Old 06-16-2010, 09:36 PM   #3
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Sizing and best way to run wire for sub panel


I am thinking that 2/0 is about right. I am not in front of my chart atm, but 2/0 should be sufficient for that.

I dont understand why you want to couple copper to alum......just run 280 ft of alum...Unless your code doesnt allow it. Also if you are getting this inspected, you MAY have to put DB cable AND Conduit. This is a popular trend among inspectors here in my area....Make sure about it.

If you are looking for prices, call supply houses and ask for 2/0 URD 4 (FOUR) Wire.....if they say no such thing exists, tell them you want 2/0 URD 3 (Three) wire with ONE 2/0 USE added to it. You will need to have 4 wires going to the subfeed. Plus a ground rod from the panel.

Another thing you can do is this to save a decent amount of cash. Get #2AWG URD/USE (as described above) and just put it on an 80amp circuit.....Might be a hell of a lot cheaper as 2/0 URD is somewhat hard to come by.....Also, 80amp breakers are generally cheaper than 100 amps......just a thought....Im sure you are doing this already, but you should get a Main Lug panel, not a Main Breaker.

Another thing you might want to look at is this:

1.25" PVC and using #2 SER wire....with 80 amp OR 100 amp and 2/0 SER.

Just another thought.

Youll have to contact your local inspector (if you pulled a permit) and get back with the requirements for buried subfeeds.


Dunno how much you know or experienced about this but there are a few other ways to reduce costs....I know at our supply house we dont stock 2/0 but stock #2....and its wayyyy cheaper...
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Old 06-16-2010, 10:06 PM   #4
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Sizing and best way to run wire for sub panel


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Im sure you are doing this already, but you should get a Main Lug panel, not a Main Breaker.
I would do a main breaker panel myself. You must have a disconnect at the out building or stay below the 6 breaker rule. With a breaker panel you have all the bases covered for very little more $.
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Old 06-16-2010, 10:33 PM   #5
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Sizing and best way to run wire for sub panel


Thanks for catching that. I believe I got confused with it being an out building. Subfeeds in the same structure do not need a main breaker.
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Old 06-16-2010, 10:35 PM   #6
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Sizing and best way to run wire for sub panel


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I would do a main breaker panel myself. You must have a disconnect at the out building or stay below the 6 breaker rule. With a breaker panel you have all the bases covered for very little more $.
Depending on size also. He might be hard pressed to find a MB panel rated for 80amps. If he goes to 100, those are usually about 20 circuits min.....

You might want to look into a Main Lug and back feed the panel with an 80A breaker.
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Old 06-16-2010, 10:40 PM   #7
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Sizing and best way to run wire for sub panel


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Also if you are getting this inspected, you MAY have to put DB cable AND Conduit. This is a popular trend among inspectors here in my area....Make sure about it.
sure would like to know what code rule they use to justify that mash up. The point of DB wire is so you do not have to use conduit and if you are using conduit, there is no reason to use DB wire.
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Old 06-16-2010, 10:43 PM   #8
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Sizing and best way to run wire for sub panel


I know for a fact some inspectors around Dayton and Miami Valley require it. Ive heard a few electricians come in and ***** about having to rip up a finished Sub feed. Now we caution all people doing subfeeds about it and tell em to call the inspector and ask. Dunno if it is Ohio or local. I think its absolutely dumb and a pain in the ass as URD is hard to work with.
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Old 06-16-2010, 11:27 PM   #9
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Sizing and best way to run wire for sub panel


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Originally Posted by LyonsElecSupply View Post
I know for a fact some inspectors around Dayton and Miami Valley require it. Ive heard a few electricians come in and ***** about having to rip up a finished Sub feed. Now we caution all people doing subfeeds about it and tell em to call the inspector and ask. Dunno if it is Ohio or local. I think its absolutely dumb and a pain in the ass as URD is hard to work with.
It's not that I'm doubting you. I would like to know how they justify the requirement. While an inspector is the AHJ, that does not give them the right to make up rules. What the AHJ position allows them to do is to interpret the existing rules, if appropriate. They can't just make up whatever they want and start enforcing their own rules.

If they couldn't come up with a rule to support their claim, I suspect I would be telling them to get over themselves and take it over their head if necessary. The costs to remove and reinstall an underground service could be quite costly. I'm afraid I would have to contest the action with the state.

Some inspectors get a God complex and if nobody argues, it just gets worse.
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Old 06-17-2010, 02:53 AM   #10
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Sizing and best way to run wire for sub panel


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Originally Posted by LyonsElecSupply View Post
I am thinking that 2/0 is about right. I am not in front of my chart atm, but 2/0 should be sufficient for that.

I dont understand why you want to couple copper to alum......just run 280 ft of alum...Unless your code doesnt allow it. Also if you are getting this inspected, you MAY have to put DB cable AND Conduit. This is a popular trend among inspectors here in my area....Make sure about it.

If you are looking for prices, call supply houses and ask for 2/0 URD 4 (FOUR) Wire.....if they say no such thing exists, tell them you want 2/0 URD 3 (Three) wire with ONE 2/0 USE added to it. You will need to have 4 wires going to the subfeed. Plus a ground rod from the panel.

Another thing you can do is this to save a decent amount of cash. Get #2AWG URD/USE (as described above) and just put it on an 80amp circuit.....Might be a hell of a lot cheaper as 2/0 URD is somewhat hard to come by.....Also, 80amp breakers are generally cheaper than 100 amps......just a thought....Im sure you are doing this already, but you should get a Main Lug panel, not a Main Breaker.

Another thing you might want to look at is this:

1.25" PVC and using #2 SER wire....with 80 amp OR 100 amp and 2/0 SER.

Just another thought.

Youll have to contact your local inspector (if you pulled a permit) and get back with the requirements for buried subfeeds.


Dunno how much you know or experienced about this but there are a few other ways to reduce costs....I know at our supply house we dont stock 2/0 but stock #2....and its wayyyy cheaper...
SER is not rated for underground use even sleeved in conduit. 2008 NEC 338.12(A)(2).

Last edited by brric; 06-17-2010 at 03:06 AM.
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Old 06-18-2010, 09:50 AM   #11
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Sizing and best way to run wire for sub panel


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Originally Posted by LyonsElecSupply View Post
I am thinking that 2/0 is about right. I am not in front of my chart atm, but 2/0 should be sufficient for that.

I dont understand why you want to couple copper to alum......just run 280 ft of alum...Unless your code doesnt allow it. Also if you are getting this inspected, you MAY have to put DB cable AND Conduit. This is a popular trend among inspectors here in my area....Make sure about it.

If you are looking for prices, call supply houses and ask for 2/0 URD 4 (FOUR) Wire.....if they say no such thing exists, tell them you want 2/0 URD 3 (Three) wire with ONE 2/0 USE added to it. You will need to have 4 wires going to the subfeed. Plus a ground rod from the panel.

Another thing you can do is this to save a decent amount of cash. Get #2AWG URD/USE (as described above) and just put it on an 80amp circuit.....Might be a hell of a lot cheaper as 2/0 URD is somewhat hard to come by.....Also, 80amp breakers are generally cheaper than 100 amps......just a thought....Im sure you are doing this already, but you should get a Main Lug panel, not a Main Breaker.

Another thing you might want to look at is this:

1.25" PVC and using #2 SER wire....with 80 amp OR 100 amp and 2/0 SER.

Just another thought.

Youll have to contact your local inspector (if you pulled a permit) and get back with the requirements for buried subfeeds.


Dunno how much you know or experienced about this but there are a few other ways to reduce costs....I know at our supply house we dont stock 2/0 but stock #2....and its wayyyy cheaper...
I was thinking of going the 80 amp route as well. When you say use #2 wire.. you mean copper right? I think that would be too small in aluminum. Also I didn't realize that you can run URD in a house, I guess if its in conduit it is fine then?

Thanks,
Chuck
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Old 06-18-2010, 10:03 AM   #12
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Sizing and best way to run wire for sub panel


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Originally Posted by cschwer View Post
I was thinking of going the 80 amp route as well. When you say use #2 wire.. you mean copper right? I think that would be too small in aluminum. Also I didn't realize that you can run URD in a house, I guess if its in conduit it is fine then?

Thanks,
Chuck
You can NOT run URD inside the house.
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Old 06-18-2010, 10:38 AM   #13
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Sizing and best way to run wire for sub panel


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Originally Posted by brric View Post
You can NOT run URD inside the house.
Yea, thats what I thought originally, so back to my original question, I would need to connect the URD wire to the wire running into the house, how do I do this? some type of disconnect box is what I assumed I would need.

Chuck
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Old 07-14-2010, 08:11 AM   #14
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Sizing and best way to run wire for sub panel


Thanks for all the replies so far,

So I guess my plan is to run 3 #2 copper wires in pvc conduit all the way with an 80 amp breaker. What size do I need for the ground wire and what size for the conduit?

Also, can I run cat5 and coax cable in the same trench or do you think I'll get interference?

Thanks,
Chuck

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