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Old 03-22-2012, 08:08 PM   #1
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2/3 romex, 125A feeder


Finding more problems while doing a remodel/addition. Was doing my load calcs for the new (under roof) addition and when inspecting panel (house built 1998), 2/3 wg Romex was run for a 200a subpanel with 125a breaker at the disconnect.

Now of course its "been fine" for 14 years, but it needs to be fixed, AC 37a, pool pump 1 14a, pool pump 2 12a, water heater 22a....plus lighting loads, 2 refriderators, electric dryer.

125a will be fine so to make it right, i have a semi-creative solution.

For the addition I will use the current 2/3 and install a 100a subpanel...check.

I will run new, properly sized wire for the old panel....so my plan to save money (approx 100ft run) is to use 2/0-2/0-2/0-1 aluminum SER.

It will be through a very large attic space so bending radius wont be an issue, and it is steep pitch (12/12) so I can easily run it where the rafters and joists meet, or otherwise protect it.

Is there any reason I wouldn't want to use aluminum in this situation? seems that that cost savings is about 80 percent!

thanks!
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Old 03-22-2012, 08:32 PM   #2
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2/3 romex, 125A feeder


Why change out the sub-panel at all? A waste of time and resources.

You could merely change out that 125 Amp breaker for a 100, provided you ensure the connected load is 95 Amps or less .... (are those pool pumps 120 or 240 Volts?)

As for that 2/0, you can NOT use it for a 125 Amp load either. You'll have to limit the connected load to 115 or less.
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Old 03-22-2012, 09:14 PM   #3
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2/3 romex, 125A feeder


I would also reduce the breaker to 100 and keep the rest the way it is.
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Old 03-22-2012, 09:15 PM   #4
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2/3 romex, 125A feeder


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Why change out the sub-panel at all? A waste of time and resources.

You could merely change out that 125 Amp breaker for a 100, provided you ensure the connected load is 95 Amps or less .... (are those pool pumps 120 or 240 Volts?)

As for that 2/0, you can NOT use it for a 125 Amp load either. You'll have to limit the connected load to 115 or less.
A new sub panel is going in regardless for the attic addition. Instead of running new wire to the new sub panel, the new plan is to use the old 2/3 for the new 100a subpanel.

The OLD 200A subpanel (main lug, 125a breaker in disconnect) feeds half of the house, it will remain as is, but will need a new feeder.

Why is 2/0-2/0-2/0-1 SER aluminum no good for 125a feeder for subpanel...everything I've found says it should be, and that the 75 deg rating is applicable (SER cable and over 100a equipment on both ends).
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Old 03-22-2012, 09:21 PM   #5
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2/3 romex, 125A feeder


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I would also reduce the breaker to 100 and keep the rest the way it is.
as mentioned, I have to put in an additional 100 amp panel anyway for an addition....the old and new panels will be about 10ft apart but 1 story up. The run to the disconnect is 100ft from the current panel and will be 100ft from the proposed panel. So I have to run wire anyway, I can make both right at the same time.


The current panel cannot support the addition even if I had the full 125a.
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Old 03-22-2012, 09:36 PM   #6
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2/3 romex, 125A feeder


I am almost sure you have to use the 60C rating for the SER.
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Old 03-22-2012, 09:47 PM   #7
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2/3 romex, 125A feeder


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I am almost sure you have to use the 60C rating for the SER.
I do see that that looks like a 2011 rule if it is in contact with residential insulation, right?

In anycase, 2/0-2/0-2/0-1 aluminum SER is rated for 115 at 60...so I would *still* be able to use a 125a breaker, using next size up rule (110a and 125a being standard sizes)? Right?
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Old 03-23-2012, 01:38 AM   #8
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2/3 romex, 125A feeder


Yeah, kind of wild how the Code rules are written:

You CAN use a 2/0 aluminum feeder for a 150 Amp service to feed an entire house.....

BUT you can NOT use it for anything more than 115 Amps if installed as inside wiring in a house, and it was embedded in thermal insulation (such as in an attic). BUT (another but here), if it is not embedded in said insulation, then you can use the 75 degree rating. So strap it up keeping it out of the insulation and you're good to go!

Make sense?
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Old 03-23-2012, 08:04 AM   #9
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2/3 romex, 125A feeder


Yes, thanks!

And it is blown in rockwool, so should be easy to route it near that intersection of rafters/joists where there the insulation is not overfilled (to keep soffit vents open)...


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Originally Posted by kbsparky View Post
Yeah, kind of wild how the Code rules are written:

You CAN use a 2/0 aluminum feeder for a 150 Amp service to feed an entire house.....

BUT you can NOT use it for anything more than 115 Amps if installed as inside wiring in a house, and it was embedded in thermal insulation (such as in an attic). BUT (another but here), if it is not embedded in said insulation, then you can use the 75 degree rating. So strap it up keeping it out of the insulation and you're good to go!

Make sense?
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