# Wire size for 125a breaker



## sparks1up (May 5, 2010)

First, are you sure your new 200-amp has a busbar rated for a 125-amp breaker? Not all panels are! Most GE panel are limited to 90-amps max and Square D QO I believe is rated but double check this, Siemens panels with copper bus may be rated too, but not the standard aluminum alloy bus version. My point is check first before you buy. Just because you can physically fit the breaker in the space doesn't mean it is rated for it or that it's acceptable!

For copper #2 wire will suffice but nothing wrong with using 1/0 or 2/0 if you prefer. However you might have a hard time getting the bigger wire in the breakers lugs.


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## HouseHelper (Mar 20, 2007)

What kind of wire? Copper? Aluminum?, SE cable, THHN in conduit? need more info.
Use either #4 or #6 to the ground rod, #4 required to water line and gas (if required).


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## oregondiy (Oct 24, 2008)

I want to use aluminum se cable because of cost. I would like to know the minimum size wire to code? I was trying to research this and got a little confused with different temps and such. It seems like I found conflicting info, some said 1/0 and some 2/0.

I will check that my new panel can handle the 125a breaker. 
I already bought a breaker, a cutler hammer br2125, it will accept up to a 2/0 wire size. 
The 200a panel I bought is a cutler hammer br series 30/40.


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## Jim Port (Sep 21, 2007)

Remember that SE needs to be used at the 60 degree rating and you will need to use 310.16, not 310.15(B)(6).


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## oregondiy (Oct 24, 2008)

Thanks for the reply, so does this mean I need 1/0 or 2/0 SE aluminum?

Does the "max 200a per stab" mean I can use the 125a breaker in this panel?


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## oregondiy (Oct 24, 2008)

I called Cutler Hammer to be sure of max breaker size, they said 125A breaker was fine. 

I went and bought my 2/0 4 conductor wire, now how do I connect the 2/0 size neutral to the neutral busbar in my panel ? Is there an adaptor for the larger size wire?

Thanks


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## sparks1up (May 5, 2010)

Aluminum SE cable 1/0 meets code for residential single phase services and feeders up to 125-amp. You can find this in table 310.15 (b) (6) in NEC. In reference to Jim Port's comment, it is only rated 100-amp in table 310-16 under the 60 degree column for aluminum wire. However 310.15 (b) (6) clearly states type's SE, USE and USE-2 are included and that 1/0 is rated for 125-amps for services and feeders as I described above.


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## sparks1up (May 5, 2010)

The neutral bar should have a lug big enough. Are you sure you are not looking at the "ground bar"?


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## SD515 (Aug 17, 2008)

sparks1up said:


> Aluminum SE cable 1/0 meets code for residential single phase services and feeders up to 125-amp. You can find this in table 310.15 (b) (6) in NEC. In reference to Jim Port's comment, it is only rated 100-amp in table 310-16 under the 60 degree column for aluminum wire. However 310.15 (b) (6) clearly states type's SE, USE and USE-2 are included and that 1/0 is rated for 125-amps for services and feeders as I described above.


 You do not use Tbl 310.15 (B)(6) for residential feeders, unless that feeder serves as the main power feeder which supplies _all of the loads_ of that dwelling. In other words, every electron that house uses has to go through that feeder. Tbl 310.16 is used for most feeders encountered.


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## sparks1up (May 5, 2010)

That is not the way it is interpreted in this area.


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## SD515 (Aug 17, 2008)

What is there to interpret? Section 310.15(B)(6) clearly states what a main power feeder is for the purpose of that section, including Tbl 310.15(B)(6). Now if your local area has an amendment to that, that’s a different story. Just be careful referencing code to others, as their local area may not have the same amendments your local area does.


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## oregondiy (Oct 24, 2008)

Thanks for the help guys.

When I was wondering about connecting the 2/0 to the neutral bar I was reffering to the 2/0 that is going from the main panel to the subpanel. 

I guess what I need is called a "neutral/ground lug" that screws onto the busbar. Is this correct?


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## wareagle (Apr 11, 2011)

Sparks
Which code version are you using? It used to be the way you are quoting but either the 08 or 11 NEC changed it.


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## a7ecorsair (Jun 1, 2010)

oregondiy said:


> Thanks for the help guys.
> 
> When I was wondering about connecting the 2/0 to the neutral bar I was reffering to the 2/0 that is going from the main panel to the subpanel.
> 
> I guess what I need is called a "neutral/ground lug" that screws onto the busbar. Is this correct?


Yes..:yes:


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## Jim Port (Sep 21, 2007)

wareagle said:


> Sparks
> Which code version are you using? It used to be the way you are quoting but either the 08 or 11 NEC changed it.


Table 310.15(B)(6) has had the note that it is only used for sizing the conductors if it serve the entire load for many code cycles.


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