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Old 06-22-2011, 11:48 PM   #1
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Wire size for 125a breaker


I am adding 200a panel and feeding my existing panel as a sub panel with a 125a breaker.

Do I use 1/0 or 2/0 to feed the sub panel? It is a 42 ft distance.

One more question on grounding the 200a panel. Do use 4 ga or 6 ga to my ground rod and gas and water pipes?

Thanks in advance for the help.

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Old 06-23-2011, 06:31 AM   #2
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Wire size for 125a breaker


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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Last edited by sparks1up; 06-23-2011 at 04:00 PM.
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Old 06-23-2011, 07:20 AM   #3
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Wire size for 125a breaker


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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Old 06-23-2011, 08:25 AM   #4
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Wire size for 125a breaker


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.

Last edited by oregondiy; 06-23-2011 at 08:52 AM. Reason: I checked the panel and the only info I could find is "Max sum of breakers per stab is 200A"
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Old 06-23-2011, 09:06 AM   #5
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Wire size for 125a breaker


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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Old 06-23-2011, 09:20 AM   #6
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Wire size for 125a breaker


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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Old 06-23-2011, 11:04 AM   #7
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Wire size for 125a breaker


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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Old 06-23-2011, 04:35 PM   #8
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Wire size for 125a breaker


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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Old 06-23-2011, 04:37 PM   #9
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Wire size for 125a breaker


The neutral bar should have a lug big enough. Are you sure you are not looking at the "ground bar"?
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Old 06-23-2011, 07:47 PM   #10
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Wire size for 125a breaker


Quote:
Originally Posted by sparks1up View Post
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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Old 06-24-2011, 05:51 AM   #11
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Wire size for 125a breaker


That is not the way it is interpreted in this area.
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Old 06-25-2011, 07:45 AM   #12
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Wire size for 125a breaker


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, thatís 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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Old 06-25-2011, 09:20 AM   #13
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Wire size for 125a breaker


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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Old 06-25-2011, 10:42 AM   #14
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Wire size for 125a breaker


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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Old 06-25-2011, 12:22 PM   #15
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Wire size for 125a breaker


Quote:
Originally Posted by oregondiy View Post
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..

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