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Old 11-13-2012, 12:38 AM   #1
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Panel upgrade - wire and breaker size


Hello!

I am re-doing all electrical in my house. I am installing a new 200A meter socket load center on the outside and a 200A sub panel inside the home. Per the city's load calc sheet the determined load for the subpanel will be 102A.
The distance between the meter main panel and the sub panel is 35-40' (as the cable will run).
My assumption would be to best go up to 125A breaker size in the main load center and sizing the feeder appropriately, to protect for future expansion in the sub panel.
I would prefer for the cable between the two panels to be run exposed (not in conduit) through the attic, which is really just a low crawl space. I was planning on using SER aluminum cable. Would you have any other suggestions?
Looking in the code I was not sure which temperature rating would apply (60 C or 75C) and if I can go with 1/0 cable or if I will have to use 2/0?

Alternatively, could you let me know what I could choose as the minimum wire and breaker size for the calculated 102A load?

Thank you very much!

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Old 11-13-2012, 05:28 AM   #2
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Panel upgrade - wire and breaker size


For the sub panel 1/0 AL is good for 125a but I would up size it a little more like a 150a 2/0 AL just because there's not much of a price difference

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Old 11-13-2012, 07:08 AM   #3
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Panel upgrade - wire and breaker size


I wouldn't bother with anything less than 4/0 Al.
Everything else is rated 200 amps, why short change yourself for a few dollars?
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Old 11-13-2012, 08:00 AM   #4
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Panel upgrade - wire and breaker size


UNLESS you are installing an additional breaker to feed the sub-panel (and not using the feed-thru lugs) then you must stick with a 200 Amp capacity cable.

This means using at least a #4/0 cable, and then using any sub-panel that is smaller is a waste of resources.

Got pix of your outside box?
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Old 11-13-2012, 09:50 PM   #5
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Panel upgrade - wire and breaker size


Quote:
Originally Posted by kbsparky View Post
UNLESS you are installing an additional breaker to feed the sub-panel (and not using the feed-thru lugs) then you must stick with a 200 Amp capacity cable.

This means using at least a #4/0 cable, and then using any sub-panel that is smaller is a waste of resources.

Got pix of your outside box?
I was planning on installing an additional circuit breaker in the feeder panel.

I do not have pictures because the panel is not installed and I haven't even bought it yet.

What would be the price difference between 1/0, 2/0 and 4/0 for the length of cable I need?
Should I go with SER cable?
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Old 11-14-2012, 05:07 AM   #6
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Panel upgrade - wire and breaker size


I'd be willing to bet that the price difference between a 100, 125, and 150 Amp breaker is much more than the wire size price difference.

IF you can get a feed-thru panel, and not have to use an additional outside breaker, that would be more cost effective.
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Old 11-14-2012, 10:31 PM   #7
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Panel upgrade - wire and breaker size


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I'd be willing to bet that the price difference between a 100, 125, and 150 Amp breaker is much more than the wire size price difference.

IF you can get a feed-thru panel, and not have to use an additional outside breaker, that would be more cost effective.
Do they have feed through panels that in addition also have spaces for breakers in the panel to feed additional panels? I want to install a solar system down the road which will need to tie into the main feeder panel.
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Old 11-15-2012, 04:46 AM   #8
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Yes, they do. I use `em all the time.

One such beastie is Square D RC816F200CH

Home Depot has `em.
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Old 11-16-2012, 02:44 AM   #9
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Yes, they do. I use `em all the time.

One such beastie is Square D RC816F200CH

Home Depot has `em.
Thanks for the info! Could you also name alternative units you have used and which you deem good?

Also, what is a good place to buy 4/0 feeder cable? I can't find good pricing online. Is this something I should buy at a store because of the weight? I will need about 40ft.
Is SER cable the best option for me since I want to run it exposed in my crawl-space-type attic?
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Old 11-16-2012, 03:27 AM   #10
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Panel upgrade - wire and breaker size


Personally, I don't like using SER cable. I prefer to install PVC conduit, and use type XHHW individual conductors.

Buying cut lengths of wire is not something to do online. Best to find a local wholesale supplier.
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Old 11-16-2012, 07:06 AM   #11
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Home Depot will cut you ser cable.
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Old 11-17-2012, 10:56 PM   #12
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Panel upgrade - wire and breaker size


Quote:
Originally Posted by bobelectric View Post
Home Depot will cut you ser cable.
All I can find at home depot is 2/0.

Quote:
Originally Posted by kbsparky View Post
Personally, I don't like using SER cable. I prefer to install PVC conduit, and use type XHHW individual conductors.

Buying cut lengths of wire is not something to do online. Best to find a local wholesale supplier.
I like this way also, but I have so many turns to take and it will run through a very low attic in which I can only lay down and crawl. Because of this, I also initially considered using smaller wire and using a breaker. I will have to do some tight bends. Do you not like SER cable because of the rigidity? Are there other downsides?

Thanks for all your help and sorry for the repeated questioning. I am new to the installation of this part of the electrical system.

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