What size of wire do I use?

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Old 11-04-07, 05:44 AM
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What size of wire do I use?

What wire do I use for underground service through 1 1/2 inch conduit, from a 200A Main Service Panel running 85 feet to a Sub Panel.

For 100A service what size and type of alum wire and what size copper ground wire would I need? What size and type of copper wire would I need?

For 125A service what size and type of alum wire and what size copper ground wire would I need? What size and type of copper wire would I need?

One more question. The service entrance will come in through an exterior wall and then turn and go up 3 feet to the sub-panel in a stud bay.
Does the wire in the stud bay need to be enclosed in conduit or is it left exposed? Thanks for your help.
 
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Old 11-04-07, 06:53 AM
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Just about any book on wiring is going to have charts of wire size based on current. Your asking these questions shows you have insufficient knowledge to be doing such work. Please pick up and read a couple books on wiring before proceeding.
 
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Old 11-04-07, 07:16 AM
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Originally Posted by mick7 View Post
What wire do I use for underground service through 1 1/2 inch conduit, from a 200A Main Service Panel running 85 feet to a Sub Panel.
Is the sub-panel in the same building as the main panel, or are you running power to a out-building?

steve
 
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Old 11-04-07, 08:28 AM
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Sub-panel will be in an out-building.
 
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Old 11-04-07, 01:19 PM
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Also has 25 feet of #4 copper buried in the slab foundation and tied to the rebar.
 
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Old 11-04-07, 04:17 PM
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Not a bad idea...

Originally Posted by mitch17 View Post
Just about any book on wiring is going to have charts of wire size based on current. Your asking these questions shows you have insufficient knowledge to be doing such work. Please pick up and read a couple books on wiring before proceeding.
Here's what I've heard:

"Rule of thumb for wire runs under 50ft: 14ga for 15A, 12Ga for 20, 10 for 30, 8 for 40, 6 for 50, etc. "

But of course, better to read it in a book than find it on the internet!
 
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Old 11-04-07, 04:27 PM
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Sorry madman.

Your rule is wrong and there is no rule of thumb. The only rule that counts is the rule of the NEC and it does not match your version of ampacity.
 
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Old 11-04-07, 05:07 PM
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or this...

also see...

http://www.mikeholt.com/technical.ph...aceway%20Chart

which I think comports with what I stated...
 
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Old 11-04-07, 05:10 PM
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Originally Posted by nap View Post
Sorry madman.

Your rule is wrong and there is no rule of thumb. The only rule that counts is the rule of the NEC and it does not match your version of ampacity.
Nap,

I'm sure my rule of thumb is flawed, which is why it is a rule of thumb, and not the law...

Do you have some helpful advise other than not to follow rule of thumbs?? Could you perhaps maybe reference some pages/sections of the NEC, since clearly that is the bible to answer this question?
 
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Old 11-04-07, 05:46 PM
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Old 11-04-07, 07:04 PM
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Sorry mad, not trying to be mean but the bottom line is the requirements are in the code. Rules of thumb can get you a red tag from the inspector and a lot of wasted money as well as other problems.

I hesitate offering much advice here as the OP does not seem to be very knowledgable about the subject and really should understand what is going on before doing any work. It is a matter of life and death.

for reference, NEC table 310.16 and annex C of the 2005 code. The problem is there are other factors to include that are not so cut and dry.
 
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Old 11-04-07, 07:05 PM
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I'll just call my inspector tomorrow and ask him, seems nobody here can come up with the answer.
 
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Old 11-04-07, 09:03 PM
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Mick, the point that you are missing is that you are asking questions in a way that makes it quite clear that you have not read much in the way of a standard basic wiring book. Electrical installations involve numerous details, and there is absolutely no way that we can tell you all of the details that you've missed. To describe the total of the details that you need to know would take a book. The _best_ that we can do is answer the specific questions that you place here, and hope that you've read the books.

I will do my best to answer your specific questions, but I do so explicitly stating that until you've read some basic wiring books, you should not purchase any materials or start this project. Instead you should do the reading and planning required.

Because you are running conductors in _conduit_, you do not need to worry about specific cable assemblies, sunlight resistance, direct burial, etc. The only requirement is that the conductors be suitable for a _wet_ location, since an outdoor or underground conduit will very often be wet.

You need wet rated conductors, most commonly type THWN (normally multiply rated THHN/THWN/MTW, but the key is that the rating letters include THWN), or perhaps XHHW or THHW etc. If you have trouble finding THHN/THWN, then look for the other sort of wet rated insulation.

You need to determine the terminal temperature rating of the breakers. Likely these are 75C terminations, but you _must_ confirm this. Assuming that you have 75C terminations, then for a 100A feeder you need #3 Cu or #1Al conductors. For a 125A feeder you need #1Cu or #2/0Al conductors.

For the equipment grounding conductor, for a 100A feeder you need #8Cu, and for a 125A feeder you need #6Cu.

What you are installing is _not_ a service. That is reserved for the main connection between the power company and your equipment. You are installing a feeder.

The conductors must be in a conduit or raceway for the entire length from source panel to destination panel. You cannot have these conductors sitting unprotected in the stud bay. The conduit or raceway system must be properly attached to the various panels. The conduit or raceway system must be completely assembled prior to installing any conductors.

If you use Aluminium conductors, then you must only use terminals rated for Aluminium, and carefully follow all termination instructions for those terminations. A torque wrench is recommended. Conductor termination compound is recommended.

-Jon
 
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